On 2/7/23 17:48, Mark Cave-Ayland wrote:
The MacOS toolbox ROM calculates the number of branches that can be executed
per millisecond as part of its timer calibration. Since modern hosts are
considerably quicker than original hardware, the negative counter reaches zero
before the calibration completes leading to division by zero later in
CALCULATESLOD.
Instead of trying to fudge the timing loop (which won't work for
TimeDBRA/TimeSCCDB
anyhow), use the pattern of access to the VIA1 registers to detect when
SETUPTIMEK
has finished executing and write some well-known good timer values to TimeDBRA
and TimeSCCDB taken from real hardware with a suitable scaling factor.
Signed-off-by: Mark Cave-Ayland <mark.cave-ayl...@ilande.co.uk>
---
hw/misc/mac_via.c | 115 ++++++++++++++++++++++++++++++++++++++
hw/misc/trace-events | 1 +
include/hw/misc/mac_via.h | 3 +
3 files changed, 119 insertions(+)
diff --git a/hw/misc/mac_via.c b/hw/misc/mac_via.c
index baeb73eeb3..766a32a95d 100644
--- a/hw/misc/mac_via.c
+++ b/hw/misc/mac_via.c
@@ -16,6 +16,7 @@
*/
#include "qemu/osdep.h"
+#include "exec/address-spaces.h"
#include "migration/vmstate.h"
#include "hw/sysbus.h"
#include "hw/irq.h"
+/*
+ * Addresses and real values for TimeDBRA/TimeSCCB to allow timer calibration
+ * to succeed (NOTE: both values have been multiplied by 3 to cope with the
+ * speed of QEMU execution on a modern host
+ */
+#define MACOS_TIMEDBRA 0xd00
+#define MACOS_TIMESCCB 0xd02
+
+#define MACOS_TIMEDBRA_VALUE (0x2a00 * 3)
+#define MACOS_TIMESCCB_VALUE (0x079d * 3)
+
+static bool via1_is_toolbox_timer_calibrated(void)
+{
+ /*
+ * Indicate whether the MacOS toolbox has been calibrated by checking
+ * for the value of our magic constants
+ */
+ uint16_t timedbra = lduw_be_phys(&address_space_memory, MACOS_TIMEDBRA);
+ uint16_t timesccdb = lduw_be_phys(&address_space_memory, MACOS_TIMESCCB);
Rather than using the global address_space_memory (which we secretly
try to remove entirely), could we pass a MemoryRegion link property
to the VIA1 device?
