QEMU fails to boot DR DOS Plus since 0.6.1

[Roy Tam]

The commit in r1049 (serial interrupt fix (Hampa Hug)) prevents booting Digital Research DOS Plus.

[Anthony Liguori (anthony-codemonkey)]

This patch doesn't seem correct as the spec is pretty clear that THRE interrupt enable is set to high, then an interrupt is rased if LSR.THRE=1. Does the following also make DOSPlus boot again:

diff --git a/hw/serial.c b/hw/serial.c
index 9102edb..b0ac52f 100644
--- a/hw/serial.c
+++ b/hw/serial.c
@@ -401,7 +401,8 @@ static void serial_ioport_write(void *opaque, uint32_t addr,
                      s->poll_msl = 0;
                 }
             }
- if (s->lsr & UART_LSR_THRE) {
+ if (s->ier & UART_IER_THRI &&
+ s->lsr & UART_LSR_THRE) {
                 s->thr_ipending = 1;
                 serial_update_irq(s);
             }

[Roy Tam (roytam)]

> This patch doesn't seem correct as the spec is pretty clear that THRE interrupt enable is set to high, then an interrupt is rased if LSR.THRE=1. Does the following also make DOSPlus boot again:

No it doesn't. Same as unpatched.

[Anthony Liguori (anthony-codemonkey)]

Can you add some debugging to see what IER is being set to?

Do you have any insight into why DR DOS Plus is failing?

[Roy Tam (roytam)]

> Can you add some debugging to see what IER is being set to?

With DEBUG_SERIAL defined, serial logs:
serial: event 2
serial: write addr=0x01 val=0x02
serial: read addr=0x01 val=0x02
serial: read addr=0x02 val=0x02
serial: write addr=0x01 val=0x00
serial: write addr=0x03 val=0x80
serial: write addr=0x00 val=0x0c
serial: write addr=0x01 val=0x00
serial: write addr=0x03 val=0x03
serial: write addr=0x04 val=0x0b
serial: read addr=0x05 val=0x60
serial: read addr=0x06 val=0xb0
serial: read addr=0x00 val=0x00
serial: write addr=0x01 val=0x0f
serial: read addr=0x02 val=0x02
serial: read addr=0x02 val=0x01
(stalls here)

[Paolo Bonzini (bonzini)]

I think the interrupt should be raised only on the rising edge of THRE.

[Thomas Huth (th-huth)]

Has this bug been fixed by this commit here:
http://git.qemu.org/?p=qemu.git;a=commitdiff;h=1645b8eee558ffe2389
?
If so, I think we could now close this bug ticket...