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lua-6502
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ADC decimal mode fixes

This commit is contained in:
Jorj Bauer 2018-06-13 16:01:35 -04:00
parent 515f4c7a98
commit 7ad050b3c2
1 changed files with 88 additions and 46 deletions
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134
6502.lua
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@ -472,6 +472,7 @@ _M.opcodes = {
-- 6502 emulation mode (e=1)
_M.getParam = {
[_M.addrmode.ILLEGAL] = function(self) return nil end,
[_M.addrmode.IMP] = function(self) return nil end,
[_M.addrmode.ACC] = function(self) return nil end,
[_M.addrmode.IMM] = function(self)
@ -698,7 +699,6 @@ _M.operations = {
end,
[_M.optype.DEX] = function(self, param)
self.X = (self.X - 1) & 0xFF
if (self.X < 0) then self.X = 0xFF end
self:setnz(self.X)
return 0
end,
@ -923,7 +923,7 @@ _M.operations = {
else
self.F = self.F & ~self.flags.C
end
v = v << 1
v = (v << 1) & 0xFF
if ((v & 0x80) ~= 0x00) then
self.F = self.F | self.flags.N
else
@ -960,7 +960,7 @@ _M.operations = {
end,
[_M.optype.ROL] = function(self, param)
local m = self:readmem(param)
local v = m << 1
local v = (m << 1) & 0xFF
if ((self.F & self.flags.C) ~= 0x00) then
v = v | 0x01
end
@ -1020,19 +1020,22 @@ _M.operations = {
return 0
end,
[_M.optype.SBC] = function(self, param)
local ret = 0
local memTemp = self:readmem(param) ~ 0xFF
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)
v = (c >> 1) ~ c
if (c < 0x100) then
c = (c + 0xa0) & 0xFF
end
v = (c ~ self.A) & 0x80
else
c = self.A + memTemp + (self.F & self.flags.C)
v = (c ~ self.A) & 0x80
@ -1057,45 +1060,89 @@ _M.operations = {
self.A = c & 0xFF
self:setnz(self.A)
return 0
return ret
end,
[_M.optype.ADC] = function(self, param)
local memTemp = self:readmem(param)
local ret = 0 -- number of additional cycles
local B = self:readmem(param)
local Cin = (self.F & self.flags.C)
local Cout -- expected carry out
local Vout -- expected oVerflow out
local Aout -- expected accumulator out
local ret = 0
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 > 0x09) then
c = (c - 0x0a) | 0x10
end
c = c + (self.A & 0xF0) + (memTemp & 0xF0)
v = (c >> 1) ~ c
if (c > 0x99) then
c = c + 0x60
end
if ((self.F & self.flags.D) == 0x00) then
-- Simple Bin mode. Thank goodness.
Aout = self.A + B + Cin
-- 'v' is described really well here:
-- http://www.righto.com/2012/12/the-6502-overflow-flag-explained.html
-- Overflow means "answer does not fit in to a signed byte".
--
-- If bits A7 and B7 are not the same, then there's never overflow.
--
-- If the signs of the two are the same,
-- but the sign of the output is different,
-- then overflow obviously happened. Both of these do that...
-- Vout = (((self.A ~ B) & 0x80) == 0x00) and ((Aout ~ B) & 0x80) or 0
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
-- Complex Dec mode.
-- Per
-- http://www.6502.org/tutorials/decimal_mode.html.
ret = 1
-- Done with the V flag processing. Calculate Aout and Cout.
Aout = (self.A & 0x0F) + (B & 0x0F) + Cin
local tmpOverflow = 0
if (Aout >= 0x0A) then
tmpOverflow = 0x10
Aout = (Aout + 0x06) & 0x0F
end
Aout = Aout | (self.A & 0xF0)
Aout = Aout + (B & 0xF0) + tmpOverflow
-- Overflow for BCD mode is calculated
-- here, before rolling over the high
-- nybble. If both A and B have the same
-- sign, and the sign for Aout is different
-- than A and B, then overflow happened.
Vout = 0
if ( ((self.A ~ B) & 0x80) == 0x00 ) then
-- A and B are of the same sign
if (((self.A ~ Aout)&0x80) ~= 0x00) then
-- A/B have a different sign from C, so it overflowed
Vout = 1
end
end
-- Back to calculating the resultant A and C
if (Aout >= 0xA0) then
Aout = Aout + 0x60
Cout = 1
else
Cout = 0
end
self.A = Aout & 0xFF
end
if (((self.A ~ memTemp) & 0x80) ~= 0x00) 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
@ -1165,7 +1212,17 @@ _M.operations = {
return 0
end,
[_M.optype.ILLEGAL] = function(self, _, _, m)
print("Programming error: unhandled opcode " .. m)
-- Treat these all as NOPs. Also emulate the
-- 65C02 behavior...
if (m == 0x02 or m == 0x22 or m == 0x42 or m == 0x62 or m == 0x82 or
m == 0xC2 or m == 0xE2 or m == 0x44 or m == 0x54 or m == 0xd4 or
m == 0xf4) then
self.pc = (self.pc + 1) & 0xFFFF
end
if (m == 0x5c or m == 0xdc or m == 0xfc) then
self.pc = (self.pc + 2) & 0xFFFF
end
return 0
end,
}
@ -1303,21 +1360,6 @@ function _M:step()
self.pc = (self.pc + 1) & 0xFFFF
local opcode = self.opcodes[m]
if (opcode[1] == self.opcodes.ILLEGAL or
opcode[2] == self.addrmode.ILLEGAL) then
print(string.format("** Illegal opcode 0x%X at address 0x%X", m, self.pc-1))
-- Special invalid opcodes tht also have arguments...
if (m == 0x02 or m == 0x22 or m == 0x42 or m == 0x62 or m == 0x82 or
m == 0xC2 or m == 0xE2 or m == 0x44 or m == 0x54 or m == 0xd4 or
m == 0xf4) then
self.pc = (self.pc + 1) & 0xFFFF
end
if (m == 0x5c or m == 0xdc or m == 0xfc) then
self.pc = (self.pc + 2) & 0xFFFF
end
m = 0xEA -- substitute NOP
opcode = self.opcodes[m]
end
-- Look at the addressing mode to determine the parameter
local param, zprelParam2 = self.getParam[opcode[2]](self)
@ -1338,7 +1380,7 @@ function _M:readmem(a)
end
function _M:writemem(a,v)
self.ram[a] = v & 0xFF
self.ram[a] = v
end
return _M