Misc. improvements, added WOZ file support to floppy emulation

[apple2] / src / v6522via.cpp

diff --git a/src/v6522via.cpp b/src/v6522via.cpp
new file mode 100644 (file)
index 0000000..f43a267
--- /dev/null
+++ b/src/v6522via.cpp
@@ -0,0 +1,198 @@
+//
+// Virtual 6522 Versatile Interface Adapter
+//
+// by James Hammons
+// (C) 2018 Underground Software
+//
+
+#include "v6522via.h"
+
+#include <string.h>            // for memset()
+#include "log.h"
+
+
+/*
+Register  Function
+--------  -------------------------
+0         Output Register B
+1         Output Register A
+2         Data Direction Register B
+3         Data Direction Register A
+4         Timer 1 Low byte counter (& latch)
+5         Timer 1 Hgh byte counter (& latch)
+6         Timer 1 Low byte latch
+7         Timer 1 Hgh byte latch (& reset IRQ flag)
+B         Aux Control Register
+D         Interrupt Flag Register
+E         Interrupt Enable Register
+
+bit 6 of ACR:
+0: Timed interrupt each time Timer 1 is loaded
+1: Continuous interrupts
+
+bit 7 enables PB7 (bit 6 controls output type):
+0: One shot output
+1: Square wave output
+*/
+
+
+V6522VIA::V6522VIA(): orb(0), ora(0), ddrb(0), ddra(0),
+       timer1counter(0), timer1latch(0), timer2counter(0),
+       acr(0), ifr(0), ier(0)
+{
+}
+
+
+void V6522VIA::Reset(void)
+{
+       memset(this, 0, sizeof(V6522VIA));
+}
+
+
+uint8_t V6522VIA::Read(uint8_t regNum)
+{
+       switch (regNum)
+       {
+       case 0x00:
+//For some reason, this prevents Ankh from loading.  Need to figure out what the MB *really* returns in its uninitialized state...
+//             return orb & ddrb;
+               return 0xFF;
+
+       case 0x01:
+               return ora & ddra;
+
+       case 0x02:
+               return ddrb;
+
+       case 0x03:
+               return ddra;
+
+       case 0x04:
+               return timer1counter & 0xFF;
+
+       case 0x05:
+               return (timer1counter & 0xFF00) >> 8;
+
+       case 0x06:
+               return timer1latch & 0xFF;
+
+       case 0x07:
+               return (timer1latch & 0xFF00) >> 8;
+
+       case 0x08:
+               return timer2counter & 0xFF;
+
+       case 0x09:
+               return (timer2counter & 0xFF00) >> 8;
+
+       case 0x0B:
+               return acr;
+
+       case 0x0D:
+               return (ifr & 0x7F) | (ifr & 0x7F ? 0x80 : 0);
+
+       case 0x0E:
+               return ier | 0x80;
+
+       default:
+               WriteLog("Unhandled 6522 register %X read (chip %d)\n", regNum, id);
+       }
+
+       return 0;
+}
+
+
+void V6522VIA::Write(uint8_t regNum, uint8_t byte)
+{
+       switch (regNum)
+       {
+       case 0x00:
+               orb = byte;
+               break;
+
+       case 0x01:
+               ora = byte;
+               break;
+
+       case 0x02:
+               ddrb = byte;
+               break;
+
+       case 0x03:
+               ddra = byte;
+               break;
+
+       case 0x04:
+               timer1latch = (timer1latch & 0xFF00) | byte;
+               break;
+
+       case 0x05:
+               timer1latch = (timer1latch & 0x00FF) | (((uint16_t)byte) << 8);
+               timer1counter = timer1latch;
+               ifr &= 0x3F; // Clear T1 interrupt flag
+               break;
+
+       case 0x06:
+               timer1latch = (timer1latch & 0xFF00)
+                       | byte;
+               break;
+
+       case 0x07:
+               timer1latch = (timer1latch & 0x00FF) | (((uint16_t)byte) << 8);
+               ifr &= 0x3F; // Clear T1 interrupt flag
+               break;
+
+       case 0x0B:
+               acr = byte;
+               break;
+
+       case 0x0D:
+               ifr &= ~byte;
+               break;
+
+       case 0x0E:
+               if (byte & 0x80)
+                       // Setting bits in the IER
+                       ier |= byte;
+               else
+                       // Clearing bits in the IER
+                       ier &= ~byte;
+
+               break;
+       default:
+               WriteLog("Unhandled 6522 register $%X write $%02X (chip %d)\n", regNum, byte, id);
+       }
+}
+
+
+bool V6522VIA::Run(uint16_t cycles)
+{
+       // This is to signal to the caller that we hit an IRQ condition
+       bool response = false;
+       bool viaT1HitZero = (timer1counter <= cycles ? true : false);
+
+       timer1counter -= cycles;
+       timer2counter -= cycles;
+
+       if (viaT1HitZero)
+       {
+               if (acr & 0x40)
+               {
+                       timer1counter += timer1latch;
+
+                       if (ier & 0x40)
+                       {
+                               ifr |= (0x80 | 0x40);
+                               response = true;
+                       }
+               }
+               else
+               {
+                       // Disable T1 interrupt
+                       ier &= 0x3F;
+               }
+       }
+
+       return response;
+}
+