The A/UX timer calibration loop runs continuously until 2 consecutive iterations
differ by at least 0x492 timer ticks. Modern hosts execute the timer calibration
loop so fast that this situation never occurs causing a hang on boot.
Use a similar method to Shoebill which is to randomly add 0x500 to the T2
counter value during calibration to enable it to eventually succeed.
Signed-off-by: Mark Cave-Ayland <mark.cave-ayl...@ilande.co.uk>
---
hw/misc/mac_via.c | 41 +++++++++++++++++++++++++++++++++++++++++
1 file changed, 41 insertions(+)
diff --git a/hw/misc/mac_via.c b/hw/misc/mac_via.c
index 94b4f5cebc..ea9d8b3aa9 100644
--- a/hw/misc/mac_via.c
+++ b/hw/misc/mac_via.c
@@ -983,6 +983,30 @@ static void
via1_timer_calibration_hack(MOS6522Q800VIA1State *v1s, int addr,
/* Looks like there has been a reset? */
v1s->timer_hack_state = 1;
}
+
+ if (addr == VIA_REG_T2CL && val == 0xf03c && size == 2) {
+ /* VIA_REG_T2CH: high byte of counter (A/UX) */
+ v1s->timer_hack_state = 5;
+ }
+ break;
+ case 5:
+ if ((addr == VIA_REG_IER && val == 0x20) || addr == VIA_REG_T2CH) {
+ /* End of A/UX timer calibration routine, or another write */
+ v1s->timer_hack_state = 6;
+ } else {
+ v1s->timer_hack_state = 0;
+ }
+ break;
+ case 6:
+ /*
+ * This is the normal post-calibration timer state once both the
+ * MacOS toolbox and A/UX have been calibrated, until we see a write
+ * to VIA_REG_PCR to suggest a reset
+ */
+ if (addr == VIA_REG_PCR && val == 0x22) {
+ /* Looks like there has been a reset? */
+ v1s->timer_hack_state = 1;
+ }
break;
default:
g_assert_not_reached();
@@ -1013,6 +1037,23 @@ static uint64_t mos6522_q800_via1_read(void *opaque,
hwaddr addr, unsigned size)
/* Quadra 800 Id */
ret = (ret & ~VIA1A_CPUID_MASK) | VIA1A_CPUID_Q800;
break;
+ case VIA_REG_T2CH:
+ if (v1s->timer_hack_state == 5) {
+ /*
+ * The A/UX timer calibration loop runs continuously until 2
+ * consecutive iterations differ by at least 0x492 timer ticks.
+ * Modern hosts execute the timer calibration loop so fast that
+ * this situation never occurs causing a hang on boot. Use a
+ * similar method to Shoebill which is to randomly add 0x500 to
+ * the T2 counter value during calibration to enable it to
+ * eventually succeed.
+ */
+ now = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
+ if (now & 1) {
+ ret += 0x5;
+ }
+ }
+ break;
}
val |= ret << ((size - i - 1) << 3);
}
--
2.30.2
