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More updates to Port B I/O of M6532, to match output from another test ROM 

on AtariAge.  It seems the documentation regarding port B is incorrect.
Pins previously defined as input/read-only *can* in fact be set as output,
which are then overridden if the console switches are pressed.

Or at least that's my understanding of it; I'm not entirely sure if this
is correct or not.


git-svn-id: svn://svn.code.sf.net/p/stella/code/trunk@2087 8b62c5a3-ac7e-4cc8-8f21-d9a121418aba
This commit is contained in:
stephena 2010-08-08 19:14:37 +00:00
parent 9089351412
commit 091ed8935e
1 changed files with 13 additions and 25 deletions
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38
src/emucore/M6532.cxx
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@ -116,7 +116,7 @@ uInt8 M6532::peek(uInt16 addr)
switch(addr & 0x07) switch(addr & 0x07)
{ {
case 0x00: // Port A I/O Register (Joystick) case 0x00: // SWCHA - Port A I/O Register (Joystick)
{ {
uInt8 value = 0x00; uInt8 value = 0x00;
@ -139,21 +139,17 @@ uInt8 M6532::peek(uInt16 addr)
return (myOutA | ~myDDRA) & value; return (myOutA | ~myDDRA) & value;
} }
case 0x01: // Port A Data Direction Register case 0x01: // SWACNT - Port A Data Direction Register
{ {
return myDDRA; return myDDRA;
} }
case 0x02: // Port B I/O Register (Console switches) case 0x02: // SWCHB - Port B I/O Register (Console switches)
{ {
// The logic here is similar to Port A I/O Register (ORA), return (myOutB | ~myDDRB) & (myConsole.switches().read() | myDDRB);
// except that only pins 2/4/5 can be configured in software
// The remaining pins are hardwired as input/read-only
// This is enforced in the ::poke method below
return (myOutB | ~myDDRB) & myConsole.switches().read();
} }
case 0x03: // Port B Data Direction Register case 0x03: // SWBCNT - Port B Data Direction Register
{ {
return myDDRB; return myDDRB;
} }
@ -231,33 +227,29 @@ bool M6532::poke(uInt16 addr, uInt8 value)
{ {
switch(addr & 0x03) switch(addr & 0x03)
{ {
case 0: // Port A I/O Register (Joystick) case 0: // SWCHA - Port A I/O Register (Joystick)
{ {
myOutA = value; myOutA = value;
setPinState(); setPinState();
break; break;
} }
case 1: // Port A Data Direction Register case 1: // SWACNT - Port A Data Direction Register
{ {
myDDRA = value; myDDRA = value;
setPinState(); setPinState();
break; break;
} }
case 2: // Port B I/O Register (Console switches) case 2: // SWCHB - Port B I/O Register (Console switches)
{ {
// Pins 2/4/5 can be set as input or output myOutB = value;
// The remaining pins are hardwired as input/read-only
myOutB = value & 0x34; // %0011 0100
break; break;
} }
case 3: // Port B Data Direction Register case 3: // SWBCNT - Port B Data Direction Register
{ {
// Pins 2/4/5 can be set as input or output myDDRB = value;
// The remaining pins are hardwired as input/read-only
myDDRB = value & 0x34; // %0011 0100
break; break;
} }
} }
@ -308,11 +300,9 @@ void M6532::setPinState()
// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
bool M6532::save(Serializer& out) const bool M6532::save(Serializer& out) const
{ {
const string& device = name();
try try
{ {
out.putString(device); out.putString(name());
// Output the RAM // Output the RAM
out.putInt(128); out.putInt(128);
@ -346,11 +336,9 @@ bool M6532::save(Serializer& out) const
// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
bool M6532::load(Serializer& in) bool M6532::load(Serializer& in)
{ {
const string& device = name();
try try
{ {
if(in.getString() != device) if(in.getString() != name())
return false; return false;
// Input the RAM // Input the RAM