mirror of https://github.com/stella-emu/stella.git
Restructured the RIOT handling of reads from INTIM and TIMINT. Also removed
all aspects of the M6532 chip that a real 2600 console doesn't use. git-svn-id: svn://svn.code.sf.net/p/stella/code/trunk@2549 8b62c5a3-ac7e-4cc8-8f21-d9a121418aba
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stephena
parent
d5269bce26
commit
b59c95062c
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@ -20,6 +20,7 @@
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#include <cassert>
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#include <iostream>
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#include "Debugger.hxx"
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#include "Console.hxx"
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#include "Settings.hxx"
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#include "Switches.hxx"
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@ -27,6 +28,8 @@
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#include "M6532.hxx"
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#define TIMER_BIT 0x80
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// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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M6532::M6532(const Console& console, const Settings& settings)
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: myConsole(console),
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@ -54,14 +57,15 @@ void M6532::reset()
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myTimer = (0xff - (mySystem->randGenerator().next() % 0xfe)) << 10;
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myIntervalShift = 10;
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myCyclesWhenTimerSet = 0;
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myInterruptEnabled = false;
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myInterruptTriggered = false;
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// Zero the I/O registers
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myDDRA = myDDRB = myOutA = myOutB = 0x00;
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// Zero the timer registers
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myOutTimer[0] = myOutTimer[1] = myOutTimer[2] = myOutTimer[3] = 0x00;
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// Zero the interrupt flag register
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myInterruptFlag = 0x00;
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}
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// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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@ -115,6 +119,8 @@ uInt8 M6532::peek(uInt16 addr)
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return myRAM[addr & 0x007f];
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}
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//cerr << Debugger::debugger().valueToString(addr&0xff, kBASE_2_8) << endl;
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switch(addr & 0x07)
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{
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case 0x00: // SWCHA - Port A I/O Register (Joystick)
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@ -147,38 +153,16 @@ uInt8 M6532::peek(uInt16 addr)
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case 0x04: // Timer Output
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case 0x06:
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{
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myInterruptTriggered = false;
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Int32 timer = timerClocks();
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// See if the timer has expired yet?
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// Note that this constant comes from z26, and corresponds to
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// 256 intervals of T1024T (ie, the maximum that the timer should hold)
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// I'm not sure why this is required, but quite a few PAL ROMs fail
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// if we just check >= 0.
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if(!(timer & 0x40000))
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{
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return (timer >> myIntervalShift) & 0xff;
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}
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else
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{
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if(timer != -1)
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myInterruptTriggered = true;
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// According to the M6532 documentation, the timer continues to count
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// down to -255 timer clocks after wraparound. However, it isn't
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// entirely clear what happens *after* if reaches -255.
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// For now, we'll let it continuously wrap around.
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return timer & 0xff;
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}
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// Update timer state and return the resulting clock
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return updateTimer();
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}
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case 0x05: // Interrupt Flag
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case 0x07:
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{
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if((timerClocks() >= 0) || (myInterruptEnabled && myInterruptTriggered))
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return 0x00;
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else
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return 0x80;
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// Update timer state and return the resulting flag(s)
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updateTimer();
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return myInterruptFlag;
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}
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default:
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@ -208,10 +192,7 @@ bool M6532::poke(uInt16 addr, uInt8 value)
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if((addr & 0x04) != 0)
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{
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if((addr & 0x10) != 0)
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{
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myInterruptEnabled = (addr & 0x08);
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setTimerRegister(value, addr & 0x03);
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}
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}
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else
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{
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@ -252,11 +233,13 @@ void M6532::setTimerRegister(uInt8 value, uInt8 interval)
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{
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static const uInt8 shift[] = { 0, 3, 6, 10 };
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myInterruptTriggered = false;
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myIntervalShift = shift[interval];
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myOutTimer[interval] = value;
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myTimer = value << myIntervalShift;
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myCyclesWhenTimerSet = mySystem->cycles();
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// Interrupt timer flag is reset when writing to the timer
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myInterruptFlag &= ~TIMER_BIT;
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}
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// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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@ -293,6 +276,32 @@ void M6532::setPinState(bool swcha)
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}
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}
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// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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uInt8 M6532::updateTimer()
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{
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// Get number of clocks since timer was set
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Int32 timer = timerClocks();
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if(timer >= 0)
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{
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// Timer hasn't expired yet
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myInterruptFlag &= ~TIMER_BIT;
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return (timer >> myIntervalShift) & 0xff;
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}
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else
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{
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if(timer < 0)
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myInterruptFlag |= TIMER_BIT;
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// According to the M6532 documentation, the timer continues to count
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// down to -255 timer clocks after wraparound. However, it isn't
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// entirely clear what happens *after* if reaches -255.
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// For now, we'll let it continuously wrap around.
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return timer & 0xff;
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}
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}
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// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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bool M6532::save(Serializer& out) const
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{
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@ -306,13 +315,12 @@ bool M6532::save(Serializer& out) const
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out.putInt(myTimer);
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out.putInt(myIntervalShift);
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out.putInt(myCyclesWhenTimerSet);
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out.putBool(myInterruptEnabled);
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out.putBool(myInterruptTriggered);
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out.putByte(myDDRA);
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out.putByte(myDDRB);
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out.putByte(myOutA);
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out.putByte(myOutB);
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out.putByte(myInterruptFlag);
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out.putByteArray(myOutTimer, 4);
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}
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catch(...)
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@ -338,13 +346,12 @@ bool M6532::load(Serializer& in)
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myTimer = in.getInt();
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myIntervalShift = in.getInt();
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myCyclesWhenTimerSet = in.getInt();
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myInterruptEnabled = in.getBool();
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myInterruptTriggered = in.getBool();
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myDDRA = in.getByte();
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myDDRB = in.getByte();
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myOutA = in.getByte();
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myOutB = in.getByte();
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myInterruptFlag = in.getByte();
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in.getByteArray(myOutTimer, 4);
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}
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catch(...)
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@ -29,7 +29,15 @@ class Settings;
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#include "System.hxx"
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/**
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RIOT
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This class models the M6532 RAM-I/O-Timer (aka RIOT) chip in the 2600
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console. Note that only the functionality used by the console is
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emulated here; several aspects of the chip are completely ignored:
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- Pin 25 (IRQ) is not connected at all, therefore all related
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items are ignored (A3 determining IRQ enable/disable, etc).
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- D6 of the Interrupt Flag is ignored, including PA7 interrupt flag (A1)
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and negative/positive edge-detection (A0)
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@author Bradford W. Mott
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@version $Id$
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@ -135,6 +143,7 @@ class M6532 : public Device
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void setTimerRegister(uInt8 data, uInt8 interval);
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void setPinState(bool shcha);
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uInt8 updateTimer();
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private:
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// Reference to the console
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@ -155,12 +164,6 @@ class M6532 : public Device
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// Indicates the number of cycles when the timer was last set
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Int32 myCyclesWhenTimerSet;
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// Indicates if a timer interrupt has been enabled
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bool myInterruptEnabled;
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// Indicates if a read from timer has taken place after interrupt occured
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bool myInterruptTriggered;
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// Data Direction Register for Port A
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uInt8 myDDRA;
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@ -173,6 +176,9 @@ class M6532 : public Device
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// Last value written to Port B
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uInt8 myOutB;
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// Interrupt Flag Register
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uInt8 myInterruptFlag;
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// Last value written to the timer registers
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uInt8 myOutTimer[4];
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@ -30,7 +30,7 @@
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#include "StateManager.hxx"
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#define STATE_HEADER "03070100state"
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#define STATE_HEADER "03070101state"
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#define MOVIE_HEADER "03030000movie"
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// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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