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ID Category [?] Severity [?] Reproducibility Date Submitted Last Update
05409 Core Major Always Jan 2, 2014, 02:13 Dec 26, 2016, 00:29
Tester jwdonal View Status Public Platform MESS (Official Binary)
Assigned To Resolution Open OS Windows Vista/7/8 (64-bit)
Status [?] Confirmed Driver
Version 0.152 Fixed in Version Build 64-bit
Summary MESS-specific 05409: SNES: SPC-700 does not set processor status flags correctly for TCLR1/TSET1 opcodes
Description From Anomie's spc700.txt we have:

  TCLR1 !a 4E 3 6 (a) = (a)&~A, ZN as for A-(a) N.....Z.
  TSET1 !a 0E 3 6 (a) = (a)|A, ZN as for A-(a) N.....Z.

It is quite clear from looking at macros OP_TCLR1 and OP_TSET1 in "mess_src_152b\src\emu\cpu\spc700\spc700.c" that the NZ flags are not being set according to A-(a) as Anomie's document states. To fix the problem I just changed the macros as follows:

/* Test and Clear Bits */
#define OP_TCLR1(BCLK, MODE) \
CLK(BCLK); \
DST = EA_##MODE(cpustate); \
FLAG_NZ = read_8_##MODE(DST); \
cpustate->spc_int16 = (short)REG_A - (short)(read_8_##MODE(DST)); \
write_8_##MODE(DST, FLAG_NZ & ~REG_A); \
FLAG_NZ = MAKE_UINT_8(cpustate->spc_int16);

/* Test and Set Bits */
#define OP_TSET1(BCLK, MODE) \
CLK(BCLK); \
DST = EA_##MODE(cpustate); \
FLAG_NZ = read_8_##MODE(DST); \
cpustate->spc_int16 = (short)REG_A - (short)(read_8_##MODE(DST)); \
write_8_##MODE(DST, FLAG_NZ | REG_A); \
FLAG_NZ = MAKE_UINT_8(cpustate->spc_int16);

However, I have not rigorously tested these changes, nor am I very familiar with exactly how the mess source works...so you might want to come up with your own solution.
Steps To Reproduce A very simple example of the NZ flags not being set correctly would be to run the following instructions on the spc-700.

  mov $00, #$55
  mov A, #$55
  tclr1 $0000

From the above, since direct-page location $00 holds the value $55 and since the accumulator A holds the value $55, the Z flag should be set to 1 based on the algorithm A-(a)...but this does not happen.
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Flags Verified with Code
Regression Version
Affected Sets / Systems SNES
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