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target/m68k: don't set SSW ATC bit for physical bus errors

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If a NuBus slot doesn't contain a card, the Quadra hardware generates a physical
bus error if the CPU attempts to access the slot address space. Both Linux and
MacOS use a separate bus error handler during NuBus accesses in order to detect
and recover when addressing empty slots.

According to the MC68040 users manual the ATC bit of the SSW is used to
distinguish between ATC faults and physical bus errors. MacOS specifically checks
the stack frame generated by a NuBus error and panics if the SSW ATC bit is set.

Update m68k_cpu_transaction_failed() so that the SSW ATC bit is not set if the
memory API returns MEMTX_DECODE_ERROR which will be used to indicate that an
access to an empty NuBus slot occurred.

Backports d6cbd8f7a19e6f0fd22a598aad992c4913f481f2
This commit is contained in:
Mark Cave-Ayland 2021-03-12 14:29:28 -05:00 committed by Lioncash
parent 945dd6fba9
commit 0be85bf91a
1 changed files with 11 additions and 1 deletions
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10
qemu/target/m68k/op_helper.c
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@ -459,7 +459,17 @@ void m68k_cpu_transaction_failed(CPUState *cs, hwaddr physaddr, vaddr addr,
if (m68k_feature(env, M68K_FEATURE_M68040)) {
env->mmu.mmusr = 0;
/*
* According to the MC68040 users manual the ATC bit of the SSW is
* used to distinguish between ATC faults and physical bus errors.
* In the case of a bus error e.g. during nubus read from an empty
* slot this bit should not be set
*/
if (response != MEMTX_DECODE_ERROR) {
env->mmu.ssw |= M68K_ATC_040;
}
/* FIXME: manage MMU table access error */
env->mmu.ssw &= ~M68K_TM_040;
if (env->sr & SR_S) { /* SUPERVISOR */