[Patch] new serial flow control

[Patch] new serial flow control

[Samuel Thibault]

[-- Attachment #1: Type: text/plain, Size: 977 bytes --]

Hi,

Some Visiobraille braille terminals (TVB) need a peculiar serial flow
control:
- There is no flow control for the PC -> device way (yes, oddly enough)
- For the device -> PC way,
  * RTS must be kept low, the device keeps CTS low as well.
  * when the device wants to send data, it raises CTS. RTS must
    be raised as well. Data can then pass, CTS and RTS are lowered.

We tried to implement that in user space, with ioctl(TIOCMBIS) & al, but
the responsiveness is too low: RTS is not raised soon enough, and the
device aborts transmission.

Here is a patch for 2.4, a 2.6 patch is coming in another mail. It
defines a CTVB flag the same way CRTSCTS is defined, letting user
space choose whether to use it or not (better ideas for the name
are welcome). This makes the device work perfectly (even better than
shipped drivers for DOS).

Applying it to vanilla kernel would be a real good thing for people
having such costly and useful hardware.

Regards,
Samuel Thibault

[-- Attachment #2: tvbpatch-2.4 --]
[-- Type: text/plain, Size: 14335 bytes --]

diff -urp linux-2.4.26-orig/drivers/char/serial.c linux-2.4.26-tvb/drivers/char/serial.c
--- linux-2.4.26-orig/drivers/char/serial.c	2004-02-18 14:59:55.000000000 +0100
+++ linux-2.4.26-tvb/drivers/char/serial.c	2004-08-18 00:48:39.000000000 +0200
@@ -789,6 +789,26 @@ static _INLINE_ void check_modem_status(
 				serial_out(info, UART_IER, info->IER);
 			}
 		}
+	} else if (info->flags & ASYNC_TVB_FLOW) {
+		if (status & UART_MSR_CTS) {
+			if (!(info->MCR & UART_MCR_RTS)) {
+				/* start of TVB frame, raise RTS to greet data */
+				info->MCR |= UART_MCR_RTS;
+				serial_out(info, UART_MCR, info->MCR);
+#if (defined(SERIAL_DEBUG_INTR) || defined(SERIAL_DEBUG_FLOW))
+				printk("TVB frame start...");
+#endif
+			}
+		} else {
+			if (info->MCR & UART_MCR_RTS) {
+				/* CTS went down, lower RTS as well */
+				info->MCR &= ~UART_MCR_RTS;
+				serial_out(info, UART_MCR, info->MCR);
+#if (defined(SERIAL_DEBUG_INTR) || defined(SERIAL_DEBUG_FLOW))
+				printk("TVB frame started...");
+#endif
+			}
+		}
 	}
 }
 
@@ -1393,7 +1413,8 @@ static int startup(struct async_struct *
 
 	info->MCR = 0;
 	if (info->tty->termios->c_cflag & CBAUD)
-		info->MCR = UART_MCR_DTR | UART_MCR_RTS;
+		info->MCR = UART_MCR_DTR |
+			(info->flags & ASYNC_TVB_FLOW ? 0 : UART_MCR_RTS);
 #ifdef CONFIG_SERIAL_MANY_PORTS
 	if (info->flags & ASYNC_FOURPORT) {
 		if (state->irq == 0)
@@ -1752,8 +1773,12 @@ static void change_speed(struct async_st
 	if (cflag & CRTSCTS) {
 		info->flags |= ASYNC_CTS_FLOW;
 		info->IER |= UART_IER_MSI;
-	} else
-		info->flags &= ~ASYNC_CTS_FLOW;
+	} else if (cflag & CTVB) {
+		info->flags |= ASYNC_TVB_FLOW;
+		info->IER |= UART_IER_MSI;
+	} else {
+		info->flags &= ~(ASYNC_CTS_FLOW|ASYNC_TVB_FLOW);
+	}
 	if (cflag & CLOCAL)
 		info->flags &= ~ASYNC_CHECK_CD;
 	else {
@@ -3057,7 +3082,8 @@ static int block_til_ready(struct tty_st
 		    (tty->termios->c_cflag & CBAUD))
 			serial_out(info, UART_MCR,
 				   serial_inp(info, UART_MCR) |
-				   (UART_MCR_DTR | UART_MCR_RTS));
+				   (UART_MCR_DTR | 
+				    (tty->termios->c_cflag & CTVB ? 0 : UART_MCR_RTS)));
 		restore_flags(flags);
 		set_current_state(TASK_INTERRUPTIBLE);
 		if (tty_hung_up_p(filp) ||
diff -urp linux-2.4.26-orig/include/asm-alpha/termbits.h linux-2.4.26-tvb/include/asm-alpha/termbits.h
--- linux-2.4.26-orig/include/asm-alpha/termbits.h	1999-01-08 20:11:45.000000000 +0100
+++ linux-2.4.26-tvb/include/asm-alpha/termbits.h	2004-08-18 00:10:30.000000000 +0200
@@ -150,6 +150,7 @@ struct termios {
 #define HUPCL	00040000
 
 #define CLOCAL	00100000
+#define CTVB	  004000000000		/* VisioBraille Terminal flow control */
 #define CRTSCTS	  020000000000		/* flow control */
 
 /* c_lflag bits */
diff -urp linux-2.4.26-orig/include/asm-arm/termbits.h linux-2.4.26-tvb/include/asm-arm/termbits.h
--- linux-2.4.26-orig/include/asm-arm/termbits.h	2000-08-13 18:54:15.000000000 +0200
+++ linux-2.4.26-tvb/include/asm-arm/termbits.h	2004-08-18 00:10:52.000000000 +0200
@@ -131,6 +131,7 @@ struct termios {
 #define  B3500000 0010016
 #define  B4000000 0010017
 #define CIBAUD	  002003600000	/* input baud rate (not used) */
+#define CTVB	  004000000000		/* VisioBraille Terminal flow control */
 #define CMSPAR    010000000000		/* mark or space (stick) parity */
 #define CRTSCTS	  020000000000		/* flow control */
 
diff -urp linux-2.4.26-orig/include/asm-cris/termbits.h linux-2.4.26-tvb/include/asm-cris/termbits.h
--- linux-2.4.26-orig/include/asm-cris/termbits.h	2003-08-27 20:53:15.000000000 +0200
+++ linux-2.4.26-tvb/include/asm-cris/termbits.h	2004-08-18 00:10:56.000000000 +0200
@@ -126,6 +126,7 @@ struct termios {
 #define  B1843200 0010006
 #define  B6250000 0010007
 #define CIBAUD	  002003600000	/* input baud rate (not used) */
+#define CTVB	  004000000000		/* VisioBraille Terminal flow control */
 #define CMSPAR	  010000000000		/* mark or space (stick) parity, PARODD => mark parity */
 #define CRTSCTS	  020000000000		/* flow control */
 
diff -urp linux-2.4.26-orig/include/asm-i386/termbits.h linux-2.4.26-tvb/include/asm-i386/termbits.h
--- linux-2.4.26-orig/include/asm-i386/termbits.h	2000-01-21 01:05:26.000000000 +0100
+++ linux-2.4.26-tvb/include/asm-i386/termbits.h	2004-08-18 00:11:00.000000000 +0200
@@ -133,6 +133,7 @@ struct termios {
 #define  B3500000 0010016
 #define  B4000000 0010017
 #define CIBAUD	  002003600000	/* input baud rate (not used) */
+#define CTVB	  004000000000		/* VisioBraille Terminal flow control */
 #define CMSPAR	  010000000000		/* mark or space (stick) parity */
 #define CRTSCTS	  020000000000		/* flow control */
 
diff -urp linux-2.4.26-orig/include/asm-ia64/termbits.h linux-2.4.26-tvb/include/asm-ia64/termbits.h
--- linux-2.4.26-orig/include/asm-ia64/termbits.h	2004-07-18 11:55:30.000000000 +0200
+++ linux-2.4.26-tvb/include/asm-ia64/termbits.h	2004-08-18 00:11:02.000000000 +0200
@@ -142,6 +142,7 @@ struct termios {
 #define  B3500000 0010016
 #define  B4000000 0010017
 #define CIBAUD	  002003600000	/* input baud rate (not used) */
+#define CTVB	  004000000000		/* VisioBraille Terminal flow control */
 #define CMSPAR	  010000000000		/* mark or space (stick) parity */
 #define CRTSCTS	  020000000000		/* flow control */
 
diff -urp linux-2.4.26-orig/include/asm-m68k/termbits.h linux-2.4.26-tvb/include/asm-m68k/termbits.h
--- linux-2.4.26-orig/include/asm-m68k/termbits.h	1999-01-08 20:11:45.000000000 +0100
+++ linux-2.4.26-tvb/include/asm-m68k/termbits.h	2004-08-18 00:11:06.000000000 +0200
@@ -134,6 +134,7 @@ struct termios {
 #define  B3500000 0010016
 #define  B4000000 0010017
 #define CIBAUD	  002003600000	/* input baud rate (not used) */
+#define CTVB	  004000000000		/* VisioBraille Terminal flow control */
 #define CMSPAR	  010000000000		/* mark or space (stick) parity */
 #define CRTSCTS	  020000000000		/* flow control */
 
diff -urp linux-2.4.26-orig/include/asm-mips/termbits.h linux-2.4.26-tvb/include/asm-mips/termbits.h
--- linux-2.4.26-orig/include/asm-mips/termbits.h	2001-09-09 19:43:01.000000000 +0200
+++ linux-2.4.26-tvb/include/asm-mips/termbits.h	2004-08-18 00:11:09.000000000 +0200
@@ -161,6 +161,7 @@ struct termios {
 #define  B3500000 0010016
 #define  B4000000 0010017
 #define CIBAUD	  002003600000	/* input baud rate (not used) */
+#define CTVB	  004000000000		/* VisioBraille Terminal flow control */
 #define CMSPAR    010000000000	/* mark or space (stick) parity */
 #define CRTSCTS	  020000000000		/* flow control */
 
diff -urp linux-2.4.26-orig/include/asm-mips64/termbits.h linux-2.4.26-tvb/include/asm-mips64/termbits.h
--- linux-2.4.26-orig/include/asm-mips64/termbits.h	2001-09-09 19:43:02.000000000 +0200
+++ linux-2.4.26-tvb/include/asm-mips64/termbits.h	2004-08-18 00:11:12.000000000 +0200
@@ -163,6 +163,7 @@ struct termios {
 #define  B3500000 0010016
 #define  B4000000 0010017
 #define CIBAUD	  002003600000	/* input baud rate (not used) */
+#define CTVB	  004000000000		/* VisioBraille Terminal flow control */
 #define CMSPAR    010000000000	/* mark or space (stick) parity */
 #define CRTSCTS	  020000000000		/* flow control */
 
diff -urp linux-2.4.26-orig/include/asm-parisc/termbits.h linux-2.4.26-tvb/include/asm-parisc/termbits.h
--- linux-2.4.26-orig/include/asm-parisc/termbits.h	2000-12-05 21:29:39.000000000 +0100
+++ linux-2.4.26-tvb/include/asm-parisc/termbits.h	2004-08-18 00:12:01.000000000 +0200
@@ -134,6 +134,7 @@ struct termios {
 #define  B3500000 0010016
 #define  B4000000 0010017
 #define CIBAUD    002003600000  /* input baud rate (not used) */
+#define CTVB      004000000000		/* VisioBraille Terminal flow control */
 #define CMSPAR    010000000000          /* mark or space (stick) parity */
 #define CRTSCTS   020000000000          /* flow control */
 
diff -urp linux-2.4.26-orig/include/asm-ppc/termbits.h linux-2.4.26-tvb/include/asm-ppc/termbits.h
--- linux-2.4.26-orig/include/asm-ppc/termbits.h	2003-06-14 02:30:26.000000000 +0200
+++ linux-2.4.26-tvb/include/asm-ppc/termbits.h	2004-08-18 00:11:20.000000000 +0200
@@ -146,6 +146,7 @@ struct termios {
 #define HUPCL	00040000
 
 #define CLOCAL	00100000
+#define CTVB	  004000000000		/* VisioBraille Terminal flow control */
 #define CRTSCTS	  020000000000		/* flow control */
 
 /* c_lflag bits */
diff -urp linux-2.4.26-orig/include/asm-ppc64/termbits.h linux-2.4.26-tvb/include/asm-ppc64/termbits.h
--- linux-2.4.26-orig/include/asm-ppc64/termbits.h	2002-08-03 23:05:34.000000000 +0200
+++ linux-2.4.26-tvb/include/asm-ppc64/termbits.h	2004-08-18 00:11:22.000000000 +0200
@@ -154,6 +154,7 @@ struct termios {
 #define HUPCL	00040000
 
 #define CLOCAL	00100000
+#define CTVB	  004000000000		/* VisioBraille Terminal flow control */
 #define CRTSCTS	  020000000000		/* flow control */
 
 /* c_lflag bits */
diff -urp linux-2.4.26-orig/include/asm-s390/termbits.h linux-2.4.26-tvb/include/asm-s390/termbits.h
--- linux-2.4.26-orig/include/asm-s390/termbits.h	2000-05-12 20:41:44.000000000 +0200
+++ linux-2.4.26-tvb/include/asm-s390/termbits.h	2004-08-18 00:11:25.000000000 +0200
@@ -141,6 +141,7 @@ struct termios {
 #define  B3500000 0010016
 #define  B4000000 0010017
 #define CIBAUD	  002003600000	/* input baud rate (not used) */
+#define CTVB	  004000000000		/* VisioBraille Terminal flow control */
 #define CMSPAR	  010000000000		/* mark or space (stick) parity */
 #define CRTSCTS	  020000000000		/* flow control */
 
diff -urp linux-2.4.26-orig/include/asm-s390x/termbits.h linux-2.4.26-tvb/include/asm-s390x/termbits.h
--- linux-2.4.26-orig/include/asm-s390x/termbits.h	2001-02-13 23:13:44.000000000 +0100
+++ linux-2.4.26-tvb/include/asm-s390x/termbits.h	2004-08-18 00:11:28.000000000 +0200
@@ -141,6 +141,7 @@ struct termios {
 #define  B3500000 0010016
 #define  B4000000 0010017
 #define CIBAUD	  002003600000	/* input baud rate (not used) */
+#define CTVB	  004000000000		/* VisioBraille Terminal flow control */
 #define CMSPAR	  010000000000		/* mark or space (stick) parity */
 #define CRTSCTS	  020000000000		/* flow control */
 
diff -urp linux-2.4.26-orig/include/asm-sh/termbits.h linux-2.4.26-tvb/include/asm-sh/termbits.h
--- linux-2.4.26-orig/include/asm-sh/termbits.h	1999-10-18 20:16:13.000000000 +0200
+++ linux-2.4.26-tvb/include/asm-sh/termbits.h	2004-08-18 00:11:30.000000000 +0200
@@ -133,6 +133,7 @@ struct termios {
 #define  B3500000 0010016
 #define  B4000000 0010017
 #define CIBAUD	  002003600000	/* input baud rate (not used) */
+#define CTVB	  004000000000		/* VisioBraille Terminal flow control */
 #define CMSPAR	  010000000000		/* mark or space (stick) parity */
 #define CRTSCTS	  020000000000		/* flow control */
 
diff -urp linux-2.4.26-orig/include/asm-sh64/termbits.h linux-2.4.26-tvb/include/asm-sh64/termbits.h
--- linux-2.4.26-orig/include/asm-sh64/termbits.h	2003-08-27 20:53:26.000000000 +0200
+++ linux-2.4.26-tvb/include/asm-sh64/termbits.h	2004-08-18 00:11:32.000000000 +0200
@@ -144,6 +144,7 @@ struct termios {
 #define  B3500000 0010016
 #define  B4000000 0010017
 #define CIBAUD	  002003600000	/* input baud rate (not used) */
+#define CTVB	  004000000000		/* VisioBraille Terminal flow control */
 #define CMSPAR	  010000000000		/* mark or space (stick) parity */
 #define CRTSCTS	  020000000000		/* flow control */
 
diff -urp linux-2.4.26-orig/include/asm-sparc/termbits.h linux-2.4.26-tvb/include/asm-sparc/termbits.h
--- linux-2.4.26-orig/include/asm-sparc/termbits.h	2002-11-29 13:24:06.000000000 +0100
+++ linux-2.4.26-tvb/include/asm-sparc/termbits.h	2004-08-18 00:12:23.000000000 +0200
@@ -173,6 +173,7 @@ struct termios {
 #define B3500000  0x00001012
 #define B4000000  0x00001013  */
 #define CIBAUD	  0x100f0000  /* input baud rate (not used) */
+#define CTVB	  0x20000000  /* VisioBraille Terminal flow control */
 #define CMSPAR	  0x40000000  /* mark or space (stick) parity */
 #define CRTSCTS	  0x80000000  /* flow control */
 
diff -urp linux-2.4.26-orig/include/asm-sparc64/termbits.h linux-2.4.26-tvb/include/asm-sparc64/termbits.h
--- linux-2.4.26-orig/include/asm-sparc64/termbits.h	2002-11-29 13:24:06.000000000 +0100
+++ linux-2.4.26-tvb/include/asm-sparc64/termbits.h	2004-08-18 00:12:36.000000000 +0200
@@ -174,6 +174,7 @@ struct termios {
 #define B3500000  0x00001012
 #define B4000000  0x00001013  */
 #define CIBAUD	  0x100f0000  /* input baud rate (not used) */
+#define CTVB	  0x20000000  /* VisioBraille Terminal flow control */
 #define CMSPAR    0x40000000  /* mark or space (stick) parity */
 #define CRTSCTS	  0x80000000  /* flow control */
 
diff -urp linux-2.4.26-orig/include/asm-x86_64/termbits.h linux-2.4.26-tvb/include/asm-x86_64/termbits.h
--- linux-2.4.26-orig/include/asm-x86_64/termbits.h	2002-11-29 13:24:06.000000000 +0100
+++ linux-2.4.26-tvb/include/asm-x86_64/termbits.h	2004-08-18 00:13:11.000000000 +0200
@@ -133,6 +133,7 @@ struct termios {
 #define  B3500000 0010016
 #define  B4000000 0010017
 #define CIBAUD	  002003600000	/* input baud rate (not used) */
+#define CTVB	  004000000000		/* VisioBraille Terminal flow control */
 #define CMSPAR	  010000000000		/* mark or space (stick) parity */
 #define CRTSCTS	  020000000000		/* flow control */
 
diff -urp linux-2.4.26-orig/include/linux/serial.h linux-2.4.26-tvb/include/linux/serial.h
--- linux-2.4.26-orig/include/linux/serial.h	2004-07-18 12:05:46.000000000 +0200
+++ linux-2.4.26-tvb/include/linux/serial.h	2004-08-18 00:34:20.000000000 +0200
@@ -141,7 +141,8 @@ struct serial_uart_config {
 #define ASYNC_CONS_FLOW		0x00800000 /* flow control for console  */
 
 #define ASYNC_BOOT_ONLYMCA	0x00400000 /* Probe only if MCA bus */
-#define ASYNC_INTERNAL_FLAGS	0xFFC00000 /* Internal flags */
+#define ASYNC_TVB_FLOW		0x00200000 /* Do VisioBraille flow control */
+#define ASYNC_INTERNAL_FLAGS	0xFFE00000 /* Internal flags */
 
 /*
  * Multiport serial configuration structure --- external structure
diff -urp linux-2.4.26-orig/include/linux/tty.h linux-2.4.26-tvb/include/linux/tty.h
--- linux-2.4.26-orig/include/linux/tty.h	2004-07-18 12:05:17.000000000 +0200
+++ linux-2.4.26-tvb/include/linux/tty.h	2004-08-18 00:23:37.000000000 +0200
@@ -224,6 +224,7 @@ struct tty_flip_buffer {
 #define C_HUPCL(tty)	_C_FLAG((tty),HUPCL)
 #define C_CLOCAL(tty)	_C_FLAG((tty),CLOCAL)
 #define C_CIBAUD(tty)	_C_FLAG((tty),CIBAUD)
+#define C_CTVB(tty)	_C_FLAG((tty),CTVB)
 #define C_CRTSCTS(tty)	_C_FLAG((tty),CRTSCTS)
 
 #define L_ISIG(tty)	_L_FLAG((tty),ISIG)

Re: [Patch] new serial flow control

[Samuel Thibault]

[-- Attachment #1: Type: text/plain, Size: 22 bytes --]

Here is patch for 2.6

[-- Attachment #2: tvbpatch-2.6 --]
[-- Type: text/plain, Size: 16089 bytes --]

diff -ur linux-2.6.8.1-orig/drivers/serial/serial_core.c linux-2.6.8.1-tvb/drivers/serial/serial_core.c
--- linux-2.6.8.1-orig/drivers/serial/serial_core.c	2004-08-14 12:54:51.000000000 +0200
+++ linux-2.6.8.1-tvb/drivers/serial/serial_core.c	2004-09-30 00:36:27.000000000 +0200
@@ -118,23 +118,6 @@
 	}
 }
 
-static inline void
-uart_update_mctrl(struct uart_port *port, unsigned int set, unsigned int clear)
-{
-	unsigned long flags;
-	unsigned int old;
-
-	spin_lock_irqsave(&port->lock, flags);
-	old = port->mctrl;
-	port->mctrl = (old & ~clear) | set;
-	if (old != port->mctrl)
-		port->ops->set_mctrl(port, port->mctrl);
-	spin_unlock_irqrestore(&port->lock, flags);
-}
-
-#define uart_set_mctrl(port,set)	uart_update_mctrl(port,set,0)
-#define uart_clear_mctrl(port,clear)	uart_update_mctrl(port,0,clear)
-
 /*
  * Startup the port.  This will be called once per open.  All calls
  * will be serialised by the per-port semaphore.
@@ -187,8 +170,13 @@
 			 * Setup the RTS and DTR signals once the
 			 * port is open and ready to respond.
 			 */
-			if (info->tty->termios->c_cflag & CBAUD)
-				uart_set_mctrl(port, TIOCM_RTS | TIOCM_DTR);
+			if (info->tty->termios->c_cflag & CBAUD) {
+				uart_set_mctrl(port, TIOCM_DTR);
+				if (info->tty->termios->c_cflag & CTVB)
+					uart_clear_mctrl(port, TIOCM_RTS);
+				else
+					uart_set_mctrl(port, TIOCM_RTS);
+			}
 		}
 
 		info->flags |= UIF_INITIALIZED;
@@ -434,6 +422,11 @@
 	else
 		state->info->flags &= ~UIF_CTS_FLOW;
 
+	if (termios->c_cflag & CTVB)
+		state->info->flags |= UIF_TVB_FLOW;
+	else
+		state->info->flags &= ~UIF_TVB_FLOW;
+
 	if (termios->c_cflag & CLOCAL)
 		state->info->flags &= ~UIF_CHECK_CD;
 	else
@@ -1180,8 +1173,8 @@
 	/* Handle transition away from B0 status */
 	if (!(old_termios->c_cflag & CBAUD) && (cflag & CBAUD)) {
 		unsigned int mask = TIOCM_DTR;
-		if (!(cflag & CRTSCTS) ||
-		    !test_bit(TTY_THROTTLED, &tty->flags))
+		if (!(cflag & CTVB) && (!(cflag & CRTSCTS) ||
+		    !test_bit(TTY_THROTTLED, &tty->flags)))
 			mask |= TIOCM_RTS;
 		uart_set_mctrl(state->port, mask);
 	}
@@ -1419,8 +1412,13 @@
 		/*
 		 * And finally enable the RTS and DTR signals.
 		 */
-		if (tty->termios->c_cflag & CBAUD)
-			uart_set_mctrl(port, TIOCM_DTR | TIOCM_RTS);
+		if (tty->termios->c_cflag & CBAUD) {
+			uart_set_mctrl(port, TIOCM_DTR);
+			if (tty->termios->c_cflag & CTVB)
+				uart_clear_mctrl(port,TIOCM_RTS);
+			else
+				uart_set_mctrl(port,TIOCM_RTS);
+		}
 	}
 }
 
diff -ur linux-2.6.8.1-orig/include/asm-alpha/termbits.h linux-2.6.8.1-tvb/include/asm-alpha/termbits.h
--- linux-2.6.8.1-orig/include/asm-alpha/termbits.h	2004-08-14 12:55:35.000000000 +0200
+++ linux-2.6.8.1-tvb/include/asm-alpha/termbits.h	2004-09-30 00:36:27.000000000 +0200
@@ -148,6 +148,7 @@
 #define HUPCL	00040000
 
 #define CLOCAL	00100000
+#define CTVB	  004000000000		/* VisioBraille Terminal flow control */
 #define CRTSCTS	  020000000000		/* flow control */
 
 /* c_lflag bits */
diff -ur linux-2.6.8.1-orig/include/asm-arm/termbits.h linux-2.6.8.1-tvb/include/asm-arm/termbits.h
--- linux-2.6.8.1-orig/include/asm-arm/termbits.h	2004-08-14 12:56:24.000000000 +0200
+++ linux-2.6.8.1-tvb/include/asm-arm/termbits.h	2004-09-30 00:36:27.000000000 +0200
@@ -132,6 +132,7 @@
 #define  B3500000 0010016
 #define  B4000000 0010017
 #define CIBAUD	  002003600000	/* input baud rate (not used) */
+#define CTVB	  004000000000		/* VisioBraille Terminal flow control */
 #define CMSPAR    010000000000		/* mark or space (stick) parity */
 #define CRTSCTS	  020000000000		/* flow control */
 
diff -ur linux-2.6.8.1-orig/include/asm-arm26/termbits.h linux-2.6.8.1-tvb/include/asm-arm26/termbits.h
--- linux-2.6.8.1-orig/include/asm-arm26/termbits.h	2004-08-14 12:55:35.000000000 +0200
+++ linux-2.6.8.1-tvb/include/asm-arm26/termbits.h	2004-09-30 00:36:27.000000000 +0200
@@ -132,6 +132,7 @@
 #define  B3500000 0010016
 #define  B4000000 0010017
 #define CIBAUD	  002003600000	/* input baud rate (not used) */
+#define CTVB	  004000000000		/* VisioBraille Terminal flow control */
 #define CMSPAR    010000000000		/* mark or space (stick) parity */
 #define CRTSCTS	  020000000000		/* flow control */
 
diff -ur linux-2.6.8.1-orig/include/asm-cris/termbits.h linux-2.6.8.1-tvb/include/asm-cris/termbits.h
--- linux-2.6.8.1-orig/include/asm-cris/termbits.h	2004-08-14 12:54:50.000000000 +0200
+++ linux-2.6.8.1-tvb/include/asm-cris/termbits.h	2004-09-30 00:36:27.000000000 +0200
@@ -108,9 +108,10 @@
  *    10 987 654 321 098 765 432 109 876 543 210
  *        |           || ||   CIBAUD, IBSHIFT=16
  *                    ibaud
+ *       |CTVB
  *     |CMSPAR
  *    | CRTSCTS
- *       x x xxx xxx x     x xx Free bits
+ *         x xxx xxx x     x xx Free bits
  */
 
 #define CBAUD	0010017
@@ -159,6 +160,7 @@
  * shifted left IBSHIFT bits.
  */
 #define IBSHIFT   16
+#define CTVB	  004000000000		/* VisioBraille Terminal flow control */
 #define CMSPAR    010000000000 /* mark or space (stick) parity - PARODD=space*/
 #define CRTSCTS	  020000000000		/* flow control */
 
diff -ur linux-2.6.8.1-orig/include/asm-h8300/termbits.h linux-2.6.8.1-tvb/include/asm-h8300/termbits.h
--- linux-2.6.8.1-orig/include/asm-h8300/termbits.h	2004-08-14 12:56:24.000000000 +0200
+++ linux-2.6.8.1-tvb/include/asm-h8300/termbits.h	2004-09-30 00:36:27.000000000 +0200
@@ -135,6 +135,7 @@
 #define  B3500000 0010016
 #define  B4000000 0010017
 #define CIBAUD	  002003600000	/* input baud rate (not used) */
+#define CTVB	  004000000000		/* VisioBraille Terminal flow control */
 #define CMSPAR	  010000000000		/* mark or space (stick) parity */
 #define CRTSCTS	  020000000000		/* flow control */
 
diff -ur linux-2.6.8.1-orig/include/asm-i386/termbits.h linux-2.6.8.1-tvb/include/asm-i386/termbits.h
--- linux-2.6.8.1-orig/include/asm-i386/termbits.h	2004-08-14 12:56:25.000000000 +0200
+++ linux-2.6.8.1-tvb/include/asm-i386/termbits.h	2004-09-30 00:36:27.000000000 +0200
@@ -134,6 +134,7 @@
 #define  B3500000 0010016
 #define  B4000000 0010017
 #define CIBAUD	  002003600000	/* input baud rate (not used) */
+#define CTVB	  004000000000		/* VisioBraille Terminal flow control */
 #define CMSPAR	  010000000000		/* mark or space (stick) parity */
 #define CRTSCTS	  020000000000		/* flow control */
 
diff -ur linux-2.6.8.1-orig/include/asm-ia64/termbits.h linux-2.6.8.1-tvb/include/asm-ia64/termbits.h
--- linux-2.6.8.1-orig/include/asm-ia64/termbits.h	2004-08-14 12:55:35.000000000 +0200
+++ linux-2.6.8.1-tvb/include/asm-ia64/termbits.h	2004-09-30 00:36:27.000000000 +0200
@@ -143,6 +143,7 @@
 #define  B3500000 0010016
 #define  B4000000 0010017
 #define CIBAUD	  002003600000	/* input baud rate (not used) */
+#define CTVB	  004000000000		/* VisioBraille Terminal flow control */
 #define CMSPAR	  010000000000		/* mark or space (stick) parity */
 #define CRTSCTS	  020000000000		/* flow control */
 
diff -ur linux-2.6.8.1-orig/include/asm-m68k/termbits.h linux-2.6.8.1-tvb/include/asm-m68k/termbits.h
--- linux-2.6.8.1-orig/include/asm-m68k/termbits.h	2004-08-14 12:56:23.000000000 +0200
+++ linux-2.6.8.1-tvb/include/asm-m68k/termbits.h	2004-09-30 00:36:27.000000000 +0200
@@ -135,6 +135,7 @@
 #define  B3500000 0010016
 #define  B4000000 0010017
 #define CIBAUD	  002003600000	/* input baud rate (not used) */
+#define CTVB	  004000000000		/* VisioBraille Terminal flow control */
 #define CMSPAR	  010000000000		/* mark or space (stick) parity */
 #define CRTSCTS	  020000000000		/* flow control */
 
diff -ur linux-2.6.8.1-orig/include/asm-mips/termbits.h linux-2.6.8.1-tvb/include/asm-mips/termbits.h
--- linux-2.6.8.1-orig/include/asm-mips/termbits.h	2004-08-14 12:54:49.000000000 +0200
+++ linux-2.6.8.1-tvb/include/asm-mips/termbits.h	2004-09-30 00:36:27.000000000 +0200
@@ -164,6 +164,7 @@
 #define  B3500000 0010016
 #define  B4000000 0010017
 #define CIBAUD	  002003600000	/* input baud rate (not used) */
+#define CTVB	  004000000000		/* VisioBraille Terminal flow control */
 #define CMSPAR    010000000000	/* mark or space (stick) parity */
 #define CRTSCTS	  020000000000		/* flow control */
 
diff -ur linux-2.6.8.1-orig/include/asm-parisc/termbits.h linux-2.6.8.1-tvb/include/asm-parisc/termbits.h
--- linux-2.6.8.1-orig/include/asm-parisc/termbits.h	2004-08-14 12:55:33.000000000 +0200
+++ linux-2.6.8.1-tvb/include/asm-parisc/termbits.h	2004-09-30 00:36:27.000000000 +0200
@@ -135,6 +135,7 @@
 #define  B3500000 0010016
 #define  B4000000 0010017
 #define CIBAUD    002003600000  /* input baud rate (not used) */
+#define CTVB	  004000000000		/* VisioBraille Terminal flow control */
 #define CMSPAR    010000000000          /* mark or space (stick) parity */
 #define CRTSCTS   020000000000          /* flow control */
 
diff -ur linux-2.6.8.1-orig/include/asm-ppc/termbits.h linux-2.6.8.1-tvb/include/asm-ppc/termbits.h
--- linux-2.6.8.1-orig/include/asm-ppc/termbits.h	2004-08-14 12:55:34.000000000 +0200
+++ linux-2.6.8.1-tvb/include/asm-ppc/termbits.h	2004-09-30 00:36:27.000000000 +0200
@@ -147,6 +147,7 @@
 #define HUPCL	00040000
 
 #define CLOCAL	00100000
+#define CTVB	  004000000000		/* VisioBraille Terminal flow control */
 #define CRTSCTS	  020000000000		/* flow control */
 
 /* c_lflag bits */
diff -ur linux-2.6.8.1-orig/include/asm-ppc64/termbits.h linux-2.6.8.1-tvb/include/asm-ppc64/termbits.h
--- linux-2.6.8.1-orig/include/asm-ppc64/termbits.h	2004-08-14 12:55:35.000000000 +0200
+++ linux-2.6.8.1-tvb/include/asm-ppc64/termbits.h	2004-09-30 00:36:27.000000000 +0200
@@ -155,6 +155,7 @@
 #define HUPCL	00040000
 
 #define CLOCAL	00100000
+#define CTVB	  004000000000		/* VisioBraille Terminal flow control */
 #define CRTSCTS	  020000000000		/* flow control */
 
 /* c_lflag bits */
diff -ur linux-2.6.8.1-orig/include/asm-s390/termbits.h linux-2.6.8.1-tvb/include/asm-s390/termbits.h
--- linux-2.6.8.1-orig/include/asm-s390/termbits.h	2004-08-14 12:56:01.000000000 +0200
+++ linux-2.6.8.1-tvb/include/asm-s390/termbits.h	2004-09-30 00:36:27.000000000 +0200
@@ -142,6 +142,7 @@
 #define  B3500000 0010016
 #define  B4000000 0010017
 #define CIBAUD	  002003600000	/* input baud rate (not used) */
+#define CTVB	  004000000000		/* VisioBraille Terminal flow control */
 #define CMSPAR	  010000000000		/* mark or space (stick) parity */
 #define CRTSCTS	  020000000000		/* flow control */
 
diff -ur linux-2.6.8.1-orig/include/asm-sh/termbits.h linux-2.6.8.1-tvb/include/asm-sh/termbits.h
--- linux-2.6.8.1-orig/include/asm-sh/termbits.h	2004-08-14 12:54:51.000000000 +0200
+++ linux-2.6.8.1-tvb/include/asm-sh/termbits.h	2004-09-30 00:36:27.000000000 +0200
@@ -134,6 +134,7 @@
 #define  B3500000 0010016
 #define  B4000000 0010017
 #define CIBAUD	  002003600000	/* input baud rate (not used) */
+#define CTVB	  004000000000		/* VisioBraille Terminal flow control */
 #define CMSPAR	  010000000000		/* mark or space (stick) parity */
 #define CRTSCTS	  020000000000		/* flow control */
 
diff -ur linux-2.6.8.1-orig/include/asm-sparc/termbits.h linux-2.6.8.1-tvb/include/asm-sparc/termbits.h
--- linux-2.6.8.1-orig/include/asm-sparc/termbits.h	2004-08-14 12:55:59.000000000 +0200
+++ linux-2.6.8.1-tvb/include/asm-sparc/termbits.h	2004-09-30 00:36:27.000000000 +0200
@@ -174,6 +174,7 @@
 #define B3500000  0x00001012
 #define B4000000  0x00001013  */
 #define CIBAUD	  0x100f0000  /* input baud rate (not used) */
+#define CTVB	  0x20000000  /* VisioBraille Terminal flow control */
 #define CMSPAR	  0x40000000  /* mark or space (stick) parity */
 #define CRTSCTS	  0x80000000  /* flow control */
 
diff -ur linux-2.6.8.1-orig/include/asm-sparc64/termbits.h linux-2.6.8.1-tvb/include/asm-sparc64/termbits.h
--- linux-2.6.8.1-orig/include/asm-sparc64/termbits.h	2004-08-14 12:54:51.000000000 +0200
+++ linux-2.6.8.1-tvb/include/asm-sparc64/termbits.h	2004-09-30 00:36:27.000000000 +0200
@@ -175,6 +175,7 @@
 #define B3500000  0x00001012
 #define B4000000  0x00001013  */
 #define CIBAUD	  0x100f0000  /* input baud rate (not used) */
+#define CTVB	  0x20000000  /* VisioBraille Terminal flow control */
 #define CMSPAR    0x40000000  /* mark or space (stick) parity */
 #define CRTSCTS	  0x80000000  /* flow control */
 
diff -ur linux-2.6.8.1-orig/include/asm-v850/termbits.h linux-2.6.8.1-tvb/include/asm-v850/termbits.h
--- linux-2.6.8.1-orig/include/asm-v850/termbits.h	2004-08-14 12:54:47.000000000 +0200
+++ linux-2.6.8.1-tvb/include/asm-v850/termbits.h	2004-09-30 00:36:27.000000000 +0200
@@ -135,6 +135,7 @@
 #define  B3500000 0010016
 #define  B4000000 0010017
 #define CIBAUD	  002003600000	/* input baud rate (not used) */
+#define CTVB	  004000000000		/* VisioBraille Terminal flow control */
 #define CMSPAR	  010000000000		/* mark or space (stick) parity */
 #define CRTSCTS	  020000000000		/* flow control */
 
diff -ur linux-2.6.8.1-orig/include/asm-x86_64/termbits.h linux-2.6.8.1-tvb/include/asm-x86_64/termbits.h
--- linux-2.6.8.1-orig/include/asm-x86_64/termbits.h	2004-08-14 12:54:48.000000000 +0200
+++ linux-2.6.8.1-tvb/include/asm-x86_64/termbits.h	2004-09-30 00:36:27.000000000 +0200
@@ -134,6 +134,7 @@
 #define  B3500000 0010016
 #define  B4000000 0010017
 #define CIBAUD	  002003600000	/* input baud rate (not used) */
+#define CTVB	  004000000000		/* VisioBraille Terminal flow control */
 #define CMSPAR	  010000000000		/* mark or space (stick) parity */
 #define CRTSCTS	  020000000000		/* flow control */
 
diff -ur linux-2.6.8.1-orig/include/linux/serial_core.h linux-2.6.8.1-tvb/include/linux/serial_core.h
--- linux-2.6.8.1-orig/include/linux/serial_core.h	2004-08-14 12:54:50.000000000 +0200
+++ linux-2.6.8.1-tvb/include/linux/serial_core.h	2004-09-30 00:41:25.000000000 +0200
@@ -264,6 +264,7 @@
  */
 #define UIF_CHECK_CD		(1 << 25)
 #define UIF_CTS_FLOW		(1 << 26)
+#define UIF_TVB_FLOW		(1 << 21)
 #define UIF_NORMAL_ACTIVE	(1 << 29)
 #define UIF_INITIALIZED		(1 << 31)
 
@@ -375,6 +376,23 @@
 #define uart_handle_sysrq_char(port,ch,regs)	(0)
 #endif
 
+static inline void
+uart_update_mctrl(struct uart_port *port, unsigned int set, unsigned int clear)
+{
+	unsigned long flags;
+	unsigned int old;
+
+	spin_lock_irqsave(&port->lock, flags);
+	old = port->mctrl;
+	port->mctrl = (old & ~clear) | set;
+	if (old != port->mctrl)
+		port->ops->set_mctrl(port, port->mctrl);
+	spin_unlock_irqrestore(&port->lock, flags);
+}
+
+#define uart_set_mctrl(port,set)	uart_update_mctrl(port,set,0)
+#define uart_clear_mctrl(port,clear)	uart_update_mctrl(port,0,clear)
+
 /*
  * We do the SysRQ and SAK checking like this...
  */
@@ -446,6 +464,11 @@
 				port->ops->stop_tx(port, 0);
 			}
 		}
+	} else if (info->flags & UIF_TVB_FLOW) {
+		if (status)
+			uart_set_mctrl(port, TIOCM_RTS);
+		else
+			uart_clear_mctrl(port, TIOCM_RTS);
 	}
 }
 
@@ -454,6 +477,7 @@
  */
 #define UART_ENABLE_MS(port,cflag)	((port)->flags & UPF_HARDPPS_CD || \
 					 (cflag) & CRTSCTS || \
+					 (cflag) & CTVB || \
 					 !((cflag) & CLOCAL))
 
 #endif
diff -ur linux-2.6.8.1-orig/include/linux/serial.h linux-2.6.8.1-tvb/include/linux/serial.h
--- linux-2.6.8.1-orig/include/linux/serial.h	2004-08-14 12:54:51.000000000 +0200
+++ linux-2.6.8.1-tvb/include/linux/serial.h	2004-09-30 00:36:27.000000000 +0200
@@ -141,7 +141,8 @@
 #define ASYNC_CONS_FLOW		0x00800000 /* flow control for console  */
 
 #define ASYNC_BOOT_ONLYMCA	0x00400000 /* Probe only if MCA bus */
-#define ASYNC_INTERNAL_FLAGS	0xFFC00000 /* Internal flags */
+#define ASYNC_TVB_FLOW		0x00200000 /* Do VisioBraille flow control */
+#define ASYNC_INTERNAL_FLAGS	0xFFE00000 /* Internal flags */
 
 /*
  * Multiport serial configuration structure --- external structure
diff -ur linux-2.6.8.1-orig/include/linux/tty.h linux-2.6.8.1-tvb/include/linux/tty.h
--- linux-2.6.8.1-orig/include/linux/tty.h	2004-08-14 12:55:32.000000000 +0200
+++ linux-2.6.8.1-tvb/include/linux/tty.h	2004-09-30 00:36:27.000000000 +0200
@@ -210,6 +210,7 @@
 #define C_CLOCAL(tty)	_C_FLAG((tty),CLOCAL)
 #define C_CIBAUD(tty)	_C_FLAG((tty),CIBAUD)
 #define C_CRTSCTS(tty)	_C_FLAG((tty),CRTSCTS)
+#define C_TVB(tty)	_C_FLAG((tty),CTVB)
 
 #define L_ISIG(tty)	_L_FLAG((tty),ISIG)
 #define L_ICANON(tty)	_L_FLAG((tty),ICANON)

Re: [Patch] new serial flow control

[Chuck Ebbert]

Samual Thibault wrote:

>+      } else if (info->flags & ASYNC_TVB_FLOW) {
>+              if (status & UART_MSR_CTS) {
>+                      if (!(info->MCR & UART_MCR_RTS)) {
>+                              /* start of TVB frame, raise RTS to greet data */
>+                              info->MCR |= UART_MCR_RTS;
>+                              serial_out(info, UART_MCR, info->MCR);
>+#if (defined(SERIAL_DEBUG_INTR) || defined(SERIAL_DEBUG_FLOW))
>+                              printk("TVB frame start...");
>+#endif
>+                      }
>+              } else {
>+                      if (info->MCR & UART_MCR_RTS) {
>+                              /* CTS went down, lower RTS as well */
>+                              info->MCR &= ~UART_MCR_RTS;
>+                              serial_out(info, UART_MCR, info->MCR);
>+#if (defined(SERIAL_DEBUG_INTR) || defined(SERIAL_DEBUG_FLOW))
>+                              printk("TVB frame started...");
>+#endif
                                                  ^^^^^^^

Shouldn't this be "ended"? ... or "end" since frame begin msg says "start"
i.e. is not past tense?


--Chuck Ebbert

Re: [Patch] new serial flow control

[Samuel Thibault]

Le mar 05 oct 2004 à 12:46:34 -0400, Chuck Ebbert a tapoté sur son clavier :
> Samual Thibault wrote:
> 
> >+      } else if (info->flags & ASYNC_TVB_FLOW) {
> >+              if (status & UART_MSR_CTS) {
> >+                      if (!(info->MCR & UART_MCR_RTS)) {
> >+                              /* start of TVB frame, raise RTS to greet data */
> >+                              info->MCR |= UART_MCR_RTS;
> >+                              serial_out(info, UART_MCR, info->MCR);
> >+#if (defined(SERIAL_DEBUG_INTR) || defined(SERIAL_DEBUG_FLOW))
> >+                              printk("TVB frame start...");
> >+#endif
> >+                      }
> >+              } else {
> >+                      if (info->MCR & UART_MCR_RTS) {
> >+                              /* CTS went down, lower RTS as well */
> >+                              info->MCR &= ~UART_MCR_RTS;
> >+                              serial_out(info, UART_MCR, info->MCR);
> >+#if (defined(SERIAL_DEBUG_INTR) || defined(SERIAL_DEBUG_FLOW))
> >+                              printk("TVB frame started...");
> >+#endif
>                                                   ^^^^^^^
> 
> Shouldn't this be "ended"? ... or "end" since frame begin msg says "start"
> i.e. is not past tense?

No: data actually pass _after_ CTS and RTS are lowered back: the flow control
only indicate the beginning of one frame.

Regards,
Samuel Thibault

Re: [Patch] new serial flow control

[Alan Cox]

On Llu, 2004-10-04 at 23:55, Samuel Thibault wrote:
> Here is patch for 2.6

How is this different from CRTSCTS ?

Re: [Patch] new serial flow control

[Sébastien Hinderer]

> > Here is patch for 2.6
> 
> How is this different from CRTSCTS ?

I'd say it is symmetric. I think the roles of RTS and CTS are exchanged.
Sam, am I right ?

Sébastien.

Re: [Patch] new serial flow control

[Samuel Thibault]

Le mer 06 oct 2004 à 09:11:10 +0200, Sébastien Hinderer a tapoté sur son clavier :
> > > Here is patch for 2.6
> > 
> > How is this different from CRTSCTS ?
> 
> I'd say it is symmetric. I think the roles of RTS and CTS are exchanged.
> Sam, am I right ?

No: CRTSCTS is a one-signal-for-each-way flow control: each
side of the link tells whether it can receive data. CTVB is a
two-signals-for-only-one-way flow control: the device tells when it
wants to send data, the PC acknowledges that, and then one frame of
data can pass.

Regards,
Samuel Thibault

Re: [Patch] new serial flow control

[Alan Cox]

On Mer, 2004-10-06 at 08:38, Samuel Thibault wrote:
> No: CRTSCTS is a one-signal-for-each-way flow control: each
> side of the link tells whether it can receive data. CTVB is a
> two-signals-for-only-one-way flow control: the device tells when it
> wants to send data, the PC acknowledges that, and then one frame of
> data can pass.

This sounds a lot like RS485 and some other related stuff. I need to
poke my pet async guru and find out if they are the same thing. If so
that would be useful.

RE: [Patch] new serial flow control

[Stuart MacDonald]

From: Alan Cox
> On Mer, 2004-10-06 at 08:38, Samuel Thibault wrote:
> > No: CRTSCTS is a one-signal-for-each-way flow control: each
> > side of the link tells whether it can receive data. CTVB is a
> > two-signals-for-only-one-way flow control: the device tells when it
> > wants to send data, the PC acknowledges that, and then one frame of
> > data can pass.
> 
> This sounds a lot like RS485 and some other related stuff. I need to
> poke my pet async guru and find out if they are the same thing. If so
> that would be useful.

RS485 is a driver-transparent electrical interface. Unfortunately the
half-duplex and master-slave(s) arrangements require some sort of
token passing to know when they can successfully transmit. This is
usually handled by the apps in some manner, although it's often wanted
to be handled by the serial driver. This could be one method of
signalling, but isn't sufficient to show RS485 operation.

I haven't seen this style of flow control before. What uses it?

..Stu

RE: [Patch] new serial flow control

[Paul Fulghum]

On Wed, 2004-10-06 at 20:30, Stuart MacDonald wrote:
> RS485 is a driver-transparent electrical interface.

Yes.

This protocol issue is independent of the electrical interface.

> I haven't seen this style of flow control before. What uses it?

terminal visio-braille (TVB)
A device for the sight impaired.

-- 
Paul Fulghum
paulkf@microgate.com

Re: [Patch] new serial flow control

[Sébastien Hinderer]

Hi,

> > I haven't seen this style of flow control before. What uses it?
> 
> terminal visio-braille (TVB)
> A device for the sight impaired.

Just to give a litle bit more precise information: this braille terminal
has been designed more than 10 years ago by the Handialog socity which is
now part of the TechniBraille/United Vision group.
Modern VisioBra"lles (with Prom of version 4 or higher) support both a
standard serial port management, and this odd flow control which was
originally designed to be used under MS-DOS, and was appropriate for doing
polling.

The integration of Samuel's patch into the kernel would allow users of
teominals containing a PROM older than 4 to use brltty with their terminal,
which would be a very useful thing, because updating such a PROM has a very
high cost.

Sébastien.

Re: [Patch] new serial flow control

[Nick Craig-Wood]

Stuart MacDonald <stuartm@connecttech.com> wrote:
>  From: Alan Cox
> > On Mer, 2004-10-06 at 08:38, Samuel Thibault wrote:
> > > No: CRTSCTS is a one-signal-for-each-way flow control: each
> > > side of the link tells whether it can receive data. CTVB is a
> > > two-signals-for-only-one-way flow control: the device tells when it
> > > wants to send data, the PC acknowledges that, and then one frame of
> > > data can pass.
> > 
> > This sounds a lot like RS485 and some other related stuff. I need to
> > poke my pet async guru and find out if they are the same thing. If so
> > that would be useful.
> 
>  RS485 is a driver-transparent electrical interface.

Yes, in theory!  In practice it isn't quite transparent due to
tristating.

These are the 4 main types of serial interface that I use regularly
RS232, RS422, RS485 4-Wire and RS485 2-Wire.

RS232 we all know and love - 12 V signalling etc

RS422 is RS232 with a different electrical interface, ie 5V
differential (2 wires per signal, eg rx+, rx- etc)

RS485 4-Wire is like RS422 but the bus has the potential to go
tri-state.  In a bus with only one master, the master can just
transmit all the time and all the slaves will listen.  However if you
want to be a slave or have multiple masters it is necessary for you to
tristate the bus.

RS485 2-Wire is like RS485 4-Wire except the transmit and receive
lines are combined into rx_tx+ and rx_tx-.  In this kind of bus it is
essential everyone tristates the line after transmitting.

For the RS485 busses there needs to be some way of telling the serial
interface hardware that you want the bus to be tristate.  This is
typically done with DTR (which isn't used for RS485 busses), DTR=1
means untristate the bus and DTR=0 means tristate it.

When used like this timing is very critical - you must de-assert DTR
as soon as the serial character has left the serial UART.  This is
difficult to do exactly in user-space.  Alternatively you can use a
specialist serial interface which will do it for you.

In practice for our applications we use RS485 in master mode which
requires no difficult control.  When we have to do RS485 in 2-Wire
mode we transmit a character and block our application to wait for it
to come back then de-assert RTS.  Thats nasty though and would be much
better done in the serial driver, where you get an interrupt at
exactly the moment the tx fifo is empty.

>  Unfortunately the half-duplex and master-slave(s) arrangements
>  require some sort of token passing to know when they can
>  successfully transmit.

It does.  Its usually done with a packet protocol and addresses.

>  This is usually handled by the apps in some manner, although it's
>  often wanted to be handled by the serial driver. This could be one
>  method of signalling, but isn't sufficient to show RS485 operation.

The tristating above should be done in the driver if possible.  The
packet protocol etc should be done in the application.

The flow control method described by the OP doesn't sound exactly like
RS485, but the timing constraints of waggling RTS are exactly the
same.

-- 
Nick Craig-Wood <nick@craig-wood.com> -- http://www.craig-wood.com/nick

RE: [Patch] new serial flow control

[Alan Cox]

On Iau, 2004-10-07 at 02:30, Stuart MacDonald wrote:
> RS485 is a driver-transparent electrical interface. Unfortunately the
> half-duplex and master-slave(s) arrangements require some sort of
> token passing to know when they can successfully transmit. This is
> usually handled by the apps in some manner, although it's often wanted
> to be handled by the serial driver. This could be one method of
> signalling, but isn't sufficient to show RS485 operation.

No its one I've seen a lot there and it turns out having dug into docs
and consulted the serial people in pointy hats that it is RS232
half-duplex mode which is one of those bits of the spec nobody ever
uses.

In this mode the DTE end (host normally) asserts RTS to request 
transmit access to the link. The DCE asserts CTS to indicate it has
finished sending bits, and the DTE then transmits.

RTS is a direction selector (RTS = 0, DCE transmit) (RTS = 1, DTE
transmit). CTS acts as the handshake to deal with the link turn around.

So that makes this much more useful. 

Alan

Re: [Patch] new serial flow control

[Samuel Thibault]

Hi,

Le jeu 07 oct 2004 à 14:00:24 +0100, Alan Cox a tapoté sur son clavier :
> In this mode the DTE end (host normally) asserts RTS to request 
> transmit access to the link. The DCE asserts CTS to indicate it has
> finished sending bits, and the DTE then transmits.
> 
> RTS is a direction selector (RTS = 0, DCE transmit) (RTS = 1, DTE
> transmit). CTS acts as the handshake to deal with the link turn around.

Hum... It seems like every role is inverted with TVB: _TVB_ raises
_CTS_ to request transmit access. The _PC_ then raises _RTS_ to
indicate it has finished sending bits, TVB then transmits.

(Yes, the cabling is correct: that's the way the DOS driver works)

Regards,
Samuel

Re: [Patch] new serial flow control

[Alan Cox]

On Maw, 2004-10-05 at 18:25, Samuel Thibault wrote:
> No: data actually pass _after_ CTS and RTS are lowered back: the flow control
> only indicate the beginning of one frame.

Ok I've pondered this somewhat. I don't think the hack proposed is the
right answer for this. I believe you should implement a simple line
discipline for this device so that it stays out of the general code.

Right now that poses a challenge but if drivers were to implement
ldisc->modem_change() or a similar callback for such events an ldisc
could then handle many of the grungy suprises and handle them once and
in one place.

Thoughts ?

Alan

Re: [Patch] new serial flow control

[Russell King]

On Thu, Oct 07, 2004 at 08:08:56PM +0100, Alan Cox wrote:
> On Maw, 2004-10-05 at 18:25, Samuel Thibault wrote:
> > No: data actually pass _after_ CTS and RTS are lowered back: the flow control
> > only indicate the beginning of one frame.
> 
> Ok I've pondered this somewhat. I don't think the hack proposed is the
> right answer for this. I believe you should implement a simple line
> discipline for this device so that it stays out of the general code.
> 
> Right now that poses a challenge but if drivers were to implement
> ldisc->modem_change() or a similar callback for such events an ldisc
> could then handle many of the grungy suprises and handle them once and
> in one place.

To me at least that sounds like a good solution.  I can't help but
wonder whether moving some of the usual modem line status change
processing should also be moved into the higher levels.  This will
probably make more sense if the "block till ready" code also moves,
which I think Ted was considering at one point.

However, that's probably something to think about later.

-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:  2.6 PCMCIA      - http://pcmcia.arm.linux.org.uk/
                 2.6 Serial core

Re: [Patch] new serial flow control

[Samuel Thibault]

Le jeu 07 oct 2004 à 20:08:56 +0100, Alan Cox a écrit:
> Right now that poses a challenge but if drivers were to implement
> ldisc->modem_change() or a similar callback for such events an ldisc
> could then handle many of the grungy suprises and handle them once and
> in one place.

Surprises like regular RTS/CTS flow control ?
Aren't there serial chips that are able to handle it themselves ? (so
that the _serial driver_ should be responsible for that, doing it in
software if needed)

I'm asking because there was some funny bug not that far ago: async
ppp people thought that xon/xoff were processed in the serial driver,
because "some serial chips may be able to handle that themselves". So
they weren't processing them. But actually it's really up to the
ldisc to process them. Thus nobody was processing it !

Regards,
Samuel Thibault

Re: [Patch] new serial flow control

[Samuel Thibault]

Le jeu 07 oct 2004 à 21:27:22 +0100, Russell King a écrit:
> I can't help but wonder whether moving some of the usual modem line
> status change processing should also be moved into the higher levels.

The more I'm thinking about it, the more I think it's not a good idea:
that would require *every* line discipline to implement hardware flow
control (just like xon/xoff), while I think they shouldn't really care
about it.

The asynchronous ppp ldisc for instance can be used on a serial line,
but can very well be used on a ssh tunnel (in which case rts/cts flow
control has no meaning).

I can understand that xon/xoff processing be implemented in ldiscs
since it is characters stuff, but one can't ask the ldisc to know
details about hardware flow control which depends on the tty it is
used on.

Regards,
Samuel Thibault

Re: [Patch] new serial flow control

[Samuel Thibault]

Le jeu 07 oct 2004 à 23:43:30 +0200, Samuel Thibault a écrit:
> I'm asking because there was some funny bug not that far ago: async
> ppp people thought that xon/xoff were processed in the serial driver,

For some record
http://groups.google.com/groups?threadm=Pine.LNX.4.10.10112042358240.2290-100000@youpi.residence.ens-lyon.fr#link15
and
http://groups.google.com/groups?threadm=Pine.LNX.4.10.10112062257590.1328-100000@youpi.residence.ens-lyon.fr
(google didn't like the subject change)

Regards,
Samuel Thibault

Re: [Patch] new serial flow control

[Russell King]

On Fri, Oct 08, 2004 at 12:08:51AM +0200, Samuel Thibault wrote:
> Le jeu 07 oct 2004 à 21:27:22 +0100, Russell King a écrit:
> > I can't help but wonder whether moving some of the usual modem line
> > status change processing should also be moved into the higher levels.
> 
> The more I'm thinking about it, the more I think it's not a good idea:
> that would require *every* line discipline to implement hardware flow
> control (just like xon/xoff), while I think they shouldn't really care
> about it.

Please note that I said "into the higher levels" and not "into line
disciplines" - I completely agree with you.  For the general case,
line disciplines do not need to know that the CTS signal has been
deasserted, or that DCD has deasserted - these are all meaningless
to the vast majority.

There are special cases though, such as the one being discussed in
this thread, where it does make sense for the line discipline to
override the default behaviour.

-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:  2.6 PCMCIA      - http://pcmcia.arm.linux.org.uk/
                 2.6 Serial core

Re: [Patch] new serial flow control

[Samuel Thibault]

Le jeu 07 oct 2004 à 20:08:56 +0100, Alan Cox wrote:
> On Maw, 2004-10-05 at 18:25, Samuel Thibault wrote:
> > No: data actually pass _after_ CTS and RTS are lowered back: the flow control
> > only indicate the beginning of one frame.
> 
> Ok I've pondered this somewhat. I don't think the hack proposed is the
> right answer for this. I believe you should implement a simple line
> discipline for this device so that it stays out of the general code.
> 
> Right now that poses a challenge but if drivers were to implement
> ldisc->modem_change() or a similar callback for such events an ldisc
> could then handle many of the grungy suprises and handle them once and
> in one place.

Serial drivers should then at least (when seeing ldisc->modem_change
!= NULL) do no RTS/CTS/DTR/etc handling at all (to avoid interfering),
and activate "MSI" for calling modem_change in the interrupt handler.

Being able to call port->ops->start/stop_tx by some way will also be
necessary, by grouping 
{
  struct uart_state *state = tty->driver_data;
  struct uart_port *port = state->port;
  tty->hw_stopped = 0;
  port->ops->start_tx(port, 0);
  uart_write_wakeup(port);
}
and its dual in some function for instance.

Regards,
Samuel Thibault