[PATCH RESEND 4/4] m68k/atari: fix SCC initialization for debug console

Finn Thain
2014-04-11T05:33:26Z

[-- Attachment #1: atari-scc-serial-debug --]
[-- Type: text/plain, Size: 3640 bytes --]

Fix SCC initialization for Atari as was previously fixed for Mac. It's
probably not practical to share more code but some attempt is made to
align the Mac and Atari variants.

Signed-off-by: Finn Thain <fthain@telegraphics.com.au>

---
This patch needs testing on Atari. It can't be tested without editing
macro definitions to enable SCC debug output (which also means disabling
MFP debug output).

The line rate is changed to 38400 baud to match the Mac code (which
follows the pmac_zilog serial console default). It would be nice to
standardize but I don't know whether this is realistic.

The 7.9872 MHz PCLK used in this patch was inferred from the existing code
as I don't have any hardware data.

---
arch/m68k/kernel/head.S | 34 ++++++++++++++++++++++------------
1 file changed, 22 insertions(+), 12 deletions(-)

Index: linux-m68k/arch/m68k/kernel/head.S
===================================================================
--- linux-m68k.orig/arch/m68k/kernel/head.S 2014-03-11 22:43:38.000000000 +1100
+++ linux-m68k/arch/m68k/kernel/head.S 2014-03-11 22:43:38.000000000 +1100
@@ -2722,6 +2722,7 @@ func_return get_new_page
#define MAC_USE_SCC_B /* Printer port */

#if defined(MAC_USE_SCC_A) || defined(MAC_USE_SCC_B)
+/* Initialisation table for SCC with 3.6864 MHz PCLK */
L(scc_initable_mac):
.byte 4,0x44 /* x16, 1 stopbit, no parity */
.byte 3,0xc0 /* receiver: 8 bpc */
@@ -2744,17 +2745,14 @@ L(scc_initable_mac):
#define USE_MFP

#if defined(USE_SCC_A) || defined(USE_SCC_B)
-#define USE_SCC
-/* Initialisation table for SCC */
-L(scc_initable):
- .byte 9,12 /* Reset */
- .byte 4,0x44 /* x16, 1 stopbit, no parity */
+/* Initialisation table for SCC with 7.9872 MHz PCLK */
+L(scc_initable_atari):
+ .byte 4,0x04 /* x1, 1 stopbit, no parity */
.byte 3,0xc0 /* receiver: 8 bpc */
.byte 5,0xe2 /* transmitter: 8 bpc, assert dtr/rts */
- .byte 9,0 /* no interrupts */
.byte 10,0 /* NRZ */
.byte 11,0x50 /* use baud rate generator */
- .byte 12,24,13,0 /* 9600 baud */
+ .byte 12,102,13,0 /* 38400 baud */
.byte 14,2,14,3 /* use master clock for BRG, enable */
.byte 3,0xc1 /* enable receiver */
.byte 5,0xea /* enable transmitter */
@@ -2800,7 +2798,7 @@ LMFP_UDR = 0xfffa2f
*/

/*
- * Initialize serial port hardware for 9600/8/1
+ * Initialize serial port hardware
*/
func_start serial_init,%d0/%d1/%a0/%a1
/*
@@ -2810,7 +2808,7 @@ func_start serial_init,%d0/%d1/%a0/%a1
* d0 = boot info offset
* CONFIG_ATARI
* a0 = address of SCC
- * a1 = Liobase address/address of scc_initable
+ * a1 = Liobase address/address of scc_initable_atari
* d0 = init data for serial port
* CONFIG_MAC
* a0 = address of SCC
@@ -2846,9 +2844,21 @@ func_start serial_init,%d0/%d1/%a0/%a1
moveb %a1@(LPSG_READ),%d0
bset #5,%d0
moveb %d0,%a1@(LPSG_WRITE)
-#elif defined(USE_SCC)
+#elif defined(USE_SCC_A) || defined(USE_SCC_B)
lea %a1@(LSCC_CTRL),%a0
- lea %pc@(L(scc_initable)),%a1
+ /* Reset SCC register pointer */
+ moveb %a0@,%d0
+ /* Reset SCC device: write register pointer then register value */
+ moveb #9,%a0@
+ moveb #0xc0,%a0@
+ /* Wait for 5 PCLK cycles, which is about 63 CPU cycles */
+ /* 5 / 7.9872 MHz = approx. 0.63 us = 63 / 100 MHz */
+ movel #32,%d0
+2:
+ subq #1,%d0
+ jne 2b
+ /* Initialize channel */
+ lea %pc@(L(scc_initable_atari)),%a1
2: moveb %a1@+,%d0
jmi 3f
moveb %d0,%a0@
@@ -3017,7 +3027,7 @@ func_start serial_putc,%d0/%d1/%a0/%a1
nop
bset #5,%d0
moveb %d0,%a1@(LPSG_WRITE)
-#elif defined(USE_SCC)
+#elif defined(USE_SCC_A) || defined(USE_SCC_B)
3: btst #2,%a1@(LSCC_CTRL)
jeq 3b
moveb %d0,%a1@(LSCC_DATA)