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[KERNAL] 65C816 native NMI sets up for native return from emulated call #342

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Jun 14, 2024
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[KERNAL] 65C816 native NMI sets up for native return from emulated call #342

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5e35646
[KERNAL] 65C816 native NMI sets up for native return from emulated call
mooinglemur Jun 10, 2024
9eb451d
native->emulated NMI doesn't expect any stack push after the RTI frame
mooinglemur Jun 10, 2024
6c66f94
cleanup
mooinglemur Jun 10, 2024
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29 changes: 15 additions & 14 deletions kernal/x16/65c816/interrupt.s
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Original file line number Diff line number Diff line change
@@ -1,3 +1,5 @@
.include "banks.inc"

.import iclall, igetin
.import cbinv, cinv, nminv
.import __irq, __irq_65c816_saved, __irq_native_ret
Expand All @@ -17,7 +19,7 @@ rom_bank = 1
.pushcpu
.setcpu "65816"

.macro c816_interrupt_impl vector
.macro c816_interrupt_impl
rep #$30 ; 16-bit accumulator and index
.I16
.A16
Expand Down Expand Up @@ -49,12 +51,11 @@ rom_bank = 1
phx ; save X and Y
phy

jmp (vector)
.A8
.I8
.endmacro

.macro irq_brk_common_impl addr, emulated_kernal_vector, emulated_kernal_impl
.macro intr_common_impl addr, emulated_kernal_vector, emulated_kernal_impl
.A16
.I16
tsx
Expand Down Expand Up @@ -82,6 +83,10 @@ rom_bank = 1
clc

php
.endmacro

.macro irq_brk_common_impl addr, emulated_kernal_vector, emulated_kernal_impl
intr_common_impl addr, emulated_kernal_vector, emulated_kernal_impl

lda $0B, S
pha
Expand All @@ -107,15 +112,17 @@ c816_nmib:
jmp (innmi)

c816_irqb:
c816_interrupt_impl inirq
c816_interrupt_impl
jmp (inirq)

.segment "C816_BRK"
c816_brk:
jmp c816_brk_impl

.segment "MEMDRV"
c816_brk_impl:
c816_interrupt_impl inbrk
c816_interrupt_impl
jmp (inbrk)

.segment "C816_COP_NATIVE"
c816_cop_native:
Expand Down Expand Up @@ -173,15 +180,9 @@ __interrupt_65c816_native_kernal_impl_ret:
rti

nnnmi:
.A16
.I16
sec
xce
.A8
.I8
clc
stz rom_bank
jmp (nminv)
c816_interrupt_impl
intr_common_impl
jmp nmi
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nnnmi needs to setup an emulation mode context and then jump to the nminv vector, not the KERNAL implementation; otherwise, NMIs in native mode won't ever execute a NMI handler written in emulation mode for the 65C02.

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@mooinglemur mooinglemur Jun 10, 2024 •
edited
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This is exactly what is done here. nmi is the target of the emulation mode NMI vector, and this function is what calls jmp (nminv) which by default leads to nnmi.

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the code for the emulation mode nmi target is in __nmi in the source, as it is copied into low RAM at init. The preservation that nmi does is minimal, so a double pla from a custom emulation mode NMI handler to clear the stack that it does should be able to rti into our fake RTI frames, one to return to native mode, and the other to return to the interrupted code.


nncop:
nnabort:
Expand Down
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