JIT 6502: BRK in 6502 IRQ leaks 17 words of FIQ stack

hoglet67 / PiTubeDirect

Bare-metal Raspberry Pi project that attaches to the Acorn TUBE interface and emulates many BBC Micro Co Processors

GNU General Public License v3.0

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Closed hoglet67 closed 1 year ago

hoglet67 commented 3 years ago

The following programs hangs after ~7740 iterations:

10 *FX 14,4
20 ON ERROR RUN
30 I%=I%+1
40 PRINT I%
50 *WIBBLE
>I%=0
>RUN
1
2
...
7742
<hangs>

This is due to a known ARM FIQ stack leak of 17 words when a tube error occurs (a BRK in the 6502 IRQ handler).

hoglet67 commented 3 years ago

Work arounds:

reset the ARM FIQ stack on 6502 reset
reset the ARM FIQ stack on TXS (I can also think of corner cases where this is bad)