minimacplus/via.c

#include <stdio.h>
#include <stdint.h>
#include "via.h"
#include "m68k.h"

void viaCbPortAWrite(unsigned int val);
void viaCbPortBWrite(unsigned int val);
void viaIrq();

#define IFR_IRQ		(1<<7)
#define IFR_T1		(1<<6)
#define IFR_T2		(1<<5)
#define IFR_CB1		(1<<4)
#define IFR_CB2		(1<<3)
#define IFR_SR		(1<<2)
#define IFR_CA1		(1<<1)
#define IFR_CA2		(1<<0)

#define PCR_NEG			0
#define PCR_NEG_NOCLR	1
#define PCR_POS			2
#define PCR_POS_NOCLR	3
#define PCR_HANDSHAKE	4
#define PCR_PULSEOUT	5
#define PCR_MAN_LO		6
#define PCR_MAN_HI		7


typedef struct {
	uint8_t ddra, ddrb;
	uint8_t ina, inb;
	uint8_t outa, outb;
	uint16_t timer1, timer2;
	uint16_t latch1, latch2;
	uint8_t ifr, ier;
	uint8_t pcr, acr;
	uint8_t controlin[2];
} Via;

static Via via;

static const char* const viaRegNames[]={
	"ORB", "ORA", "DDRB", "DDRA", "T1C-L", "T1C-H", "T1L-L", "T1L-H", "T2L-L",
	"T2C-H", "SR", "ACR", "PCR", "IFR", "IER", "ORA-NC"
};


void viaSet(int no, int mask) {
	if (no==VIA_PORTA) via.ina|=mask; else via.inb|=mask;
}

void viaClear(int no, int mask) {
	if (no==VIA_PORTA) via.ina&=~mask; else via.inb&=~mask;
}

void viaStep(int clockcycles) {
	while(clockcycles--) {
		if (via.timer1==1) {
			via.ifr|=IFR_T1;
			via.timer1=via.latch1;
		}
		if ((via.timer1!=0) || (via.acr&(1<<6))) via.timer1--;
		via.timer2--;
		if (via.timer2==0) {
			//Actually shouldn't be set when timer2 gets 0 a 2nd time... ahwell.
			via.ifr|=IFR_T2;
		}
	}
}

static void viaCheckIrq() {
	static int oldmint=0;
	int mint=(via.ifr&via.ier)&0x7F;
	if (mint) {
		via.ifr|=IFR_IRQ;
		viaIrq(1);
//		printf("VIA: Raised IRQ because masked if is %x\n", mint);
	} else if (!mint) {
		if (via.ifr&IFR_IRQ) viaIrq(0);
		via.ifr&=~IFR_IRQ;
	}
}

static int pcrFor(int no) {
	const int shift[]={0, 1, 4, 5};
	const int mask[]={1, 3, 1, 3};
	int pcr=(via.pcr>>shift[no])&mask[no];
	if (no&1) {
		if (pcr) return PCR_NEG; else return PCR_POS;
	} else {
		return pcr;
	}
}

static void accessPort(int no) {
	via.ifr&=~(no?IFR_CB1:IFR_CA1);
	int pcrca2=pcrFor(no?VIA_CB2:VIA_CA2);
	if (pcrca2==PCR_NEG || pcrca2==PCR_POS) {
		via.ifr&=~(no?IFR_CB2:IFR_CA2);
	}
	viaCheckIrq();
}

void viaControlWrite(int no, int val) {
	const int ifbits[]={IFR_CA1, IFR_CA2, IFR_CB1, IFR_CB2}; 
	int pcr=pcrFor(no);
	if (val) val=1;
	if (via.controlin[no]!=val) {
		if ( ((pcr==PCR_NEG || pcr==PCR_NEG_NOCLR) && !val) ||
			 ((pcr==PCR_POS || pcr==PCR_POS_NOCLR) && val) ) {
			via.ifr|=ifbits[no];
			viaCheckIrq();
		}
	}
	via.controlin[no]=val;
}

void viaWrite(unsigned int addr, unsigned int val) {
	if (addr==0x0) {
		//ORB
		viaCbPortBWrite(val);
		accessPort(1);
	} else if (addr==0x1) {
		//ORA
		viaCbPortAWrite(val);
		accessPort(0);
	} else if (addr==0x2) {
		//DDRB
		via.ddrb=val;
	} else if (addr==0x3) {
		//DDRA
		via.ddra=val;
	} else if (addr==0x4) {
		//T1L-L
		via.latch1=(via.latch1&0xff00)|val;
	} else if (addr==0x5) {
		//T1C-H
		via.latch1=(via.latch1&0x00ff)|(val<<8);
		via.timer1=via.latch1;
		via.ifr&=~IFR_T1;
		viaCheckIrq();
	} else if (addr==0x6) {
		//T1L-L
		via.latch1=(via.latch1&0xff00)|val;
	} else if (addr==0x7) {
		//T1L-H
		via.latch1=(via.latch1&0x00ff)|(val<<8);
		via.ifr&=~IFR_T1;
		viaCheckIrq();
	} else if (addr==0x8) {
		//T2L-l
		via.latch2=val;
	} else if (addr==0x9) {
		//T2C-H
		via.timer2=via.latch2|(val<<8);
		via.ifr&=~IFR_T2;
		viaCheckIrq();
	} else if (addr==0xa) {
		//SR
//		printf("6522: Unimplemented: Write %x to SR?\n", val);
	} else if (addr==0xb) {
		//ACR
		via.acr=val;
	} else if (addr==0xc) {
		//PCR
		via.pcr=val;
	} else if (addr==0xd) {
		//IFR
		via.ifr&=~val;
		viaCheckIrq();
	} else if (addr==0xe) {
		//IER
		if (val&0x80) {
			via.ier|=val;
		} else {
			via.ier&=~val;
		}
		via.ier&=0x7f;
		viaCheckIrq();
	} else if (addr==0xf) {
		//ORA
		viaCbPortAWrite(val);
	}
//	printf("VIA write %s val %x\n", viaRegNames[addr], val);
}


unsigned int viaRead(unsigned int addr) {
	unsigned int pc=m68k_get_reg(NULL, M68K_REG_PC);
	unsigned int val=0;
	if (addr==0x0) {
		//ORB
		val=via.inb;
		accessPort(1);
	} else if (addr==0x1) {
		//ORA
		val=via.ina;
		accessPort(0);
	} else if (addr==0x2) {
		//DDRB
		val=via.ddrb;
	} else if (addr==0x3) {
		//DDRA
		val=via.ddra;
	} else if (addr==0x4) {
		//T1L-L
		val=via.timer1&0xff;
		via.ifr&=~IFR_T1;
		viaCheckIrq();
	} else if (addr==0x5) {
		//T1C-H
		val=via.timer1>>8;
	} else if (addr==0x6) {
		//T1L-L
		val=via.latch1&0xff;
	} else if (addr==0x7) {
		//T1L-H
		val=via.latch1&0xff;
	} else if (addr==0x8) {
		//T2L-l
		val=via.timer2&0xff;
		via.ifr&=~IFR_T2;
		viaCheckIrq();
	} else if (addr==0x9) {
		//T2C-H
		val=via.timer2>>8;
	} else if (addr==0xa) {
		//SR
//		printf("6522: Unimplemented: Read from SR?\n");
	} else if (addr==0xb) {
		//ACR
		val=via.acr;
	} else if (addr==0xc) {
		//PCR
		val=via.pcr;
	} else if (addr==0xd) {
		//IFR
		val=via.ifr;
	} else if (addr==0xe) {
		//IER
		val=via.ier;
	} else if (addr==0xf) {
		//ORA
		val=via.ina;
	}
//	printf("PC %x VIA read %s val %x\n", pc, viaRegNames[addr], val);
	return val;
}