Apple-1-Tools/lua-6502
1
0
Fork 0
mirror of https://github.com/JorjBauer/lua-6502.git synced 2025-01-13 22:34:00 +00:00
Code Issues Projects Releases Wiki Activity

fixes for SBC in BCD mode

Browse Source
This commit is contained in:
Jorj Bauer 2018-06-13 18:33:51 -04:00
parent 7ad050b3c2
commit b11851912e
1 changed files with 46 additions and 26 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

72
6502.lua
View File

@ -1020,46 +1020,66 @@ _M.operations = {
return 0
end,
[_M.optype.SBC] = function(self, param)
local ret = 0
local memTemp = self:readmem(param) ~ 0xFF
local ret = 0 -- number of additional cycles
local B = self:readmem(param) ~ 0xFF
local Cin = (self.F & self.flags.C)
local Cout -- expected carry out
local Vout -- expected oVerflow out
local Aout -- expected accumulator out
local c,v
if ((self.F & self.flags.D) ~= 0x00) then
-- Decimal mode
ret = 1
c = (self.A & 0x0F) + (memTemp & 0x0F) + (self.F & self.flags.C)
if (c < 0x10) then
c = (c - 0x06) & 0x0F
end
c = c + (self.A & 0xF0) + (memTemp & 0xF0)
if (c < 0x100) then
c = (c + 0xa0) & 0xFF
end
v = (c ~ self.A) & 0x80
if ((self.F & self.flags.D) == 0x00) then
-- Simple Bin mode. Same as ADC's bin mode.
Aout = self.A + B + Cin
Vout = (self.A ~ Aout) & (B ~ Aout) & 0x80
Cout = (Aout >= 0x100) and 1 or 0
self.A = Aout & 0xFF
else
c = self.A + memTemp + (self.F & self.flags.C)
v = (c ~ self.A) & 0x80
-- Emulating decimal mode's handling of
-- invalid BCD values is tricky.
ret = 1
-- FIXME: This can probably be optimized;
-- this passes all 6502 decimal mode tests,
-- but is seemingly doing a lot of the same
-- work twice
-- First calculate the V and C flags
Aout = (self.A & 0x0F) + (B & 0x0F) + Cin
if (Aout < 0x10) then
Aout = (Aout - 0x06) & 0x0F
end
Aout = Aout + (self.A & 0xF0) + (B & 0xF0)
Vout = (self.A ~ Aout) & (B ~ Aout) & 0x80
if (Aout < 0x100) then
Aout = (Aout + 0xa0) & 0xFF
end
Cout = (Aout >= 0x100) and 1 or 0
-- Calculate the actual A output
B = self:readmem(param)
local AL = (self.A & 0x0F) - (B & 0x0F) + (Cin - 1)
Aout = self.A - B + Cin - 1
if (Aout < 0) then Aout = Aout - 0x60 end
if (AL < 0) then Aout = Aout - 0x06 end
self.A = Aout & 0xFF
end
if (((self.A ~ memTemp) & 0x80) ~= 0) then
v = 0
end
if (c > 0xFF) then
if (Cout ~= 0x00) then
self.F = self.F | self.flags.C
else
self.F = self.F & ~self.flags.C
end
if (v ~= 0x00) then
if (Vout ~= 0x00) then
self.F = self.F | self.flags.V
else
self.F = self.F & ~self.flags.V
end
self.A = c & 0xFF
self:setnz(self.A)
return ret
end,
[_M.optype.ADC] = function(self, param)