Re: [Qemu-devel] [PATCH v5 03/11] escc: introduce a selector for the register bit

["Philippe Mathieu-Daudé" <f4bug@amsat.org>]

Hi Marc, Laurent.

On Mon, Oct 29, 2018 at 2:43 PM Mark Cave-Ayland
<mark.cave-ayland@ilande.co.uk> wrote:
>
> From: Laurent Vivier <laurent@vivier.eu>
>
> On Sparc and PowerMac, the bit 0 of the address
> selects the register type (control or data) and
> bit 1 selects the channel (B or A).
>
> On m68k Macintosh, the bit 0 selects the channel and
> bit 1 the register type.
>
> This patch introduces a new parameter (bit_swap) to
> the device interface to indicate bits usage must
> be swapped between registers and channels.
>
> For the moment all the machines use the bit 0,
> but this change will be needed to emulate Quadra 800.
>
> Signed-off-by: Laurent Vivier <laurent@vivier.eu>
> ---
>  hw/char/escc.c         | 30 ++++++++++++++++++++++++------
>  include/hw/char/escc.h |  1 +
>  2 files changed, 25 insertions(+), 6 deletions(-)
>
> diff --git a/hw/char/escc.c b/hw/char/escc.c
> index 628f5f81f7..cec75b06f9 100644
> --- a/hw/char/escc.c
> +++ b/hw/char/escc.c
> @@ -42,14 +42,21 @@
>   * mouse and keyboard ports don't implement all functions and they are
>   * only asynchronous. There is no DMA.
>   *
> - * Z85C30 is also used on PowerMacs. There are some small differences
> - * between Sparc version (sunzilog) and PowerMac (pmac):
> + * Z85C30 is also used on PowerMacs and m68k Macs.
> + *
> + * There are some small differences between Sparc version (sunzilog)
> + * and PowerMac (pmac):
>   *  Offset between control and data registers
>   *  There is some kind of lockup bug, but we can ignore it
>   *  CTS is inverted
>   *  DMA on pmac using DBDMA chip
>   *  pmac can do IRDA and faster rates, sunzilog can only do 38400
>   *  pmac baud rate generator clock is 3.6864 MHz, sunzilog 4.9152 MHz
> + *
> + * Linux driver for m68k Macs is the same as for PowerMac (pmac_zilog),
> + * but registers are grouped by type and not by channel:
> + * channel is selected by bit 0 of the address (instead of bit 1)
> + * and register is selected by bit 1 of the address (instead of bit 0).

If I understand the datashit correctly, the case bit_swap=true is the
default implementation of the Z85C30,
and the current QEMU implementation (from this patch view:
bit_swap=false) is not: it is PowerMac specific.

I think the PowerMac uses an evolved Z85C30 with more precise IRQ lines.

Anyway, not a blocker, but I wanted to share my view that this model
is eventually going in an incorrect direction.
I'll try to suggest a patch to clean this during the next merge window.

Regards,

Phil.

>   */
>
>  /*
> @@ -169,6 +176,16 @@ static void handle_kbd_command(ESCCChannelState *s, int val);
>  static int serial_can_receive(void *opaque);
>  static void serial_receive_byte(ESCCChannelState *s, int ch);
>
> +static int reg_shift(ESCCState *s)
> +{
> +    return s->bit_swap ? s->it_shift + 1 : s->it_shift;
> +}
> +
> +static int chn_shift(ESCCState *s)
> +{
> +    return s->bit_swap ? s->it_shift : s->it_shift + 1;
> +}
> +
>  static void clear_queue(void *opaque)
>  {
>      ESCCChannelState *s = opaque;
> @@ -433,8 +450,8 @@ static void escc_mem_write(void *opaque, hwaddr addr,
>      int newreg, channel;
>
>      val &= 0xff;
> -    saddr = (addr >> serial->it_shift) & 1;
> -    channel = (addr >> (serial->it_shift + 1)) & 1;
> +    saddr = (addr >> reg_shift(serial)) & 1;
> +    channel = (addr >> chn_shift(serial)) & 1;
>      s = &serial->chn[channel];
>      switch (saddr) {
>      case SERIAL_CTRL:
> @@ -537,8 +554,8 @@ static uint64_t escc_mem_read(void *opaque, hwaddr addr,
>      uint32_t ret;
>      int channel;
>
> -    saddr = (addr >> serial->it_shift) & 1;
> -    channel = (addr >> (serial->it_shift + 1)) & 1;
> +    saddr = (addr >> reg_shift(serial)) & 1;
> +    channel = (addr >> chn_shift(serial)) & 1;
>      s = &serial->chn[channel];
>      switch (saddr) {
>      case SERIAL_CTRL:
> @@ -822,6 +839,7 @@ static void escc_realize(DeviceState *dev, Error **errp)
>  static Property escc_properties[] = {
>      DEFINE_PROP_UINT32("frequency", ESCCState, frequency,   0),
>      DEFINE_PROP_UINT32("it_shift",  ESCCState, it_shift,    0),
> +    DEFINE_PROP_BOOL("bit_swap",    ESCCState, bit_swap,    false),
>      DEFINE_PROP_UINT32("disabled",  ESCCState, disabled,    0),
>      DEFINE_PROP_UINT32("chnBtype",  ESCCState, chn[0].type, 0),
>      DEFINE_PROP_UINT32("chnAtype",  ESCCState, chn[1].type, 0),
> diff --git a/include/hw/char/escc.h b/include/hw/char/escc.h
> index 42aca83611..8762f61c14 100644
> --- a/include/hw/char/escc.h
> +++ b/include/hw/char/escc.h
> @@ -50,6 +50,7 @@ typedef struct ESCCState {
>
>      struct ESCCChannelState chn[2];
>      uint32_t it_shift;
> +    bool bit_swap;
>      MemoryRegion mmio;
>      uint32_t disabled;
>      uint32_t frequency;
> --
> 2.11.0
>
>