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Fixed bug in handling illegal TIA reads; the value returned should always 

'clipped' to the unused TIA bits.


git-svn-id: svn://svn.code.sf.net/p/stella/code/trunk@2099 8b62c5a3-ac7e-4cc8-8f21-d9a121418aba
This commit is contained in:
stephena 2010-08-16 19:49:32 +00:00
parent d007c3502f
commit 0a7726cb9f
2 changed files with 23 additions and 23 deletions
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3
Changes.txt
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@ -47,6 +47,9 @@
extra storage. Special thanks to Omegamatrix of AtariAge for advice
and test ROMs in this area.
* Fixed bug when reading from illegal TIA addresses; a Space Invaders
hack was showing pink enemies instead of white ones.
* Fixed bug in handling INPT4/INPT5 latches from VBLANK; a least one
ROM was working in Stella when it didn't on real hardware.

43
src/emucore/TIA.cxx
View File

@ -1169,46 +1169,42 @@ uInt8 TIA::peek(uInt16 addr)
// If pins are undriven, we start with the last databus value
// Otherwise, there is some randomness injected into the mix
uInt8 value = myTIAPinsDriven ? mySystem->getDataBusState(0xFF) :
mySystem->getDataBusState();
// In either case, we start out with D7 and D6 disabled (the only
// valid bits in a TIA read), and selectively enable them
uInt8 value = 0x3F & (!myTIAPinsDriven ? mySystem->getDataBusState() :
mySystem->getDataBusState(0xFF));
uInt16 collision = myCollision & (uInt16)myCollisionEnabledMask;
switch(addr & 0x000f)
{
case CXM0P:
value = (value & 0x3F) |
((collision & Cx_M0P1) ? 0x80 : 0x00) |
((collision & Cx_M0P0) ? 0x40 : 0x00);
value |= ((collision & Cx_M0P1) ? 0x80 : 0x00) |
((collision & Cx_M0P0) ? 0x40 : 0x00);
break;
case CXM1P:
value = (value & 0x3F) |
((collision & Cx_M1P0) ? 0x80 : 0x00) |
((collision & Cx_M1P1) ? 0x40 : 0x00);
value |= ((collision & Cx_M1P0) ? 0x80 : 0x00) |
((collision & Cx_M1P1) ? 0x40 : 0x00);
break;
case CXP0FB:
value = (value & 0x3F) |
((collision & Cx_P0PF) ? 0x80 : 0x00) |
((collision & Cx_P0BL) ? 0x40 : 0x00);
value |= ((collision & Cx_P0PF) ? 0x80 : 0x00) |
((collision & Cx_P0BL) ? 0x40 : 0x00);
break;
case CXP1FB:
value = (value & 0x3F) |
((collision & Cx_P1PF) ? 0x80 : 0x00) |
((collision & Cx_P1BL) ? 0x40 : 0x00);
value |= ((collision & Cx_P1PF) ? 0x80 : 0x00) |
((collision & Cx_P1BL) ? 0x40 : 0x00);
break;
case CXM0FB:
value = (value & 0x3F) |
((collision & Cx_M0PF) ? 0x80 : 0x00) |
((collision & Cx_M0BL) ? 0x40 : 0x00);
value |= ((collision & Cx_M0PF) ? 0x80 : 0x00) |
((collision & Cx_M0BL) ? 0x40 : 0x00);
break;
case CXM1FB:
value = (value & 0x3F) |
((collision & Cx_M1PF) ? 0x80 : 0x00) |
((collision & Cx_M1BL) ? 0x40 : 0x00);
value |= ((collision & Cx_M1PF) ? 0x80 : 0x00) |
((collision & Cx_M1BL) ? 0x40 : 0x00);
break;
case CXBLPF:
@ -1216,9 +1212,8 @@ uInt8 TIA::peek(uInt16 addr)
break;
case CXPPMM:
value = (value & 0x3F) |
((collision & Cx_P0P1) ? 0x80 : 0x00) |
((collision & Cx_M0M1) ? 0x40 : 0x00);
value |= ((collision & Cx_P0P1) ? 0x80 : 0x00) |
((collision & Cx_M0M1) ? 0x40 : 0x00);
break;
case INPT0:
@ -1260,6 +1255,8 @@ uInt8 TIA::peek(uInt16 addr)
}
default:
// This shouldn't happen, but if it does, we essentially just
// return the last databus value with bits D6 and D7 zeroed out
break;
}
return value;