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mac_via: work around underflow in TimeDBRA timing loop in SETUPTIMEK

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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-ayland@ilande.co.uk>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-ID: <20231004083806.757242-15-mark.cave-ayland@ilande.co.uk>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>
This commit is contained in:
Mark Cave-Ayland 2023-10-04 09:38:00 +01:00 • committed by Laurent Vivier
parent 994af0b2e0
commit 366d27796c
3 changed files with 119 additions and 0 deletions
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hw/misc/trace-events
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@ -272,6 +272,7 @@ via1_adb_send(const char *state, uint8_t data, const char *vadbint) "state %s da
via1_adb_receive(const char *state, uint8_t data, const char *vadbint, int status, int index, int size) "state %s data=0x%02x vADBInt=%s status=0x%x index=%d size=%d"
via1_adb_poll(uint8_t data, const char *vadbint, int status, int index, int size) "data=0x%02x vADBInt=%s status=0x%x index=%d size=%d"
via1_auxmode(int mode) "setting auxmode to %d"
via1_timer_hack_state(int state) "setting timer_hack_state to %d"
# grlib_ahb_apb_pnp.c
grlib_ahb_pnp_read(uint64_t addr, unsigned size, uint32_t value) "AHB PnP read addr:0x%03"PRIx64" size:%u data:0x%08x"