apple1-videocard-lib/lib/interrupt.h

68 lines
2.0 KiB
C
Raw Normal View History

2021-12-22 14:11:55 +00:00
#ifndef INTERRUPT_H
#define INTERRUPT_H
2021-12-08 11:53:13 +00:00
// reserve locations 0,1,2 used by the APPLE1 IRQ jump vector
// these will contain a three byte instruction "JUMP <interrupt_handler>"
// in order to make the interrupt routine not reside in zero page
2021-12-04 18:36:32 +00:00
#pragma zp_reserve(0,1,2)
// acknowledge the TMS9918 interrupt by reading the status register (see manual section 2.3.1)
#define TMS_ACK_INTERRUPT asm { lda VDP_REG }
// acknowledge the VIA 6522 interrupt by reading the T1CL register
#define VIA_ACK_INTERRUPT asm { bit VIA_T1CL }
2021-12-04 18:36:32 +00:00
2021-12-23 13:28:59 +00:00
EXPORT __address(0) byte IRQ_JUMP_OPCODE; // location 0 contains the opcode for "JMP"
EXPORT __address(1) word IRQ_JUMP_ADDRESS; // location 1 and 2 contain the jump address
2021-12-04 18:36:32 +00:00
#pragma zp_reserve(1)
#pragma zp_reserve(2)
#pragma zp_reserve(0)
2021-12-08 11:53:13 +00:00
// storage for a simple watch timer
2021-12-23 13:28:59 +00:00
EXPORT volatile byte _ticks;
EXPORT volatile byte _seconds;
EXPORT volatile byte _minutes;
EXPORT volatile byte _hours;
EXPORT volatile byte _irq_trigger;
2021-12-08 11:53:13 +00:00
// interrupt routine called every 1/60th by the CPU after TMS9918 sets the /INT pin
EXPORT __interrupt(hardware_all) void time_interrupt_handler() {
2021-12-08 11:53:13 +00:00
// update the watch
if(++_ticks == 60) {
_ticks = 0;
if(++_seconds == 60) {
_seconds = 0;
if(++_minutes == 60) {
_minutes = 0;
_hours++;
}
}
2021-12-04 18:36:32 +00:00
}
_irq_trigger = 1; // signals that an interrupt has been triggered
#ifdef TMS9918
TMS_ACK_INTERRUPT;
#endif
2021-12-14 17:40:01 +00:00
#ifdef VIA6522
VIA_ACK_INTERRUPT;
#endif
2021-12-04 18:36:32 +00:00
}
2021-12-08 11:53:13 +00:00
// safely installs the interrupt routine
void install_interrupt(word interrupt_handler) {
2021-12-04 18:36:32 +00:00
asm { sei }; // disable 6502 interrupts
IRQ_JUMP_OPCODE = 0x4C; // $4C = JUMP opcode
IRQ_JUMP_ADDRESS = interrupt_handler; // JUMP interrupt_handler
2021-12-04 18:36:32 +00:00
asm { cli }; // re-enable 6502 interrupts
}
2021-12-14 17:40:01 +00:00
// waits until IRQ is triggered
void wait_interrupt() {
// _irq_trigger = 0;
// while(_irq_trigger == 0); // waits until it's set to 1 from the interrupt handler
}
2021-12-22 14:11:55 +00:00
#endif