Hardware timer delay for Atari ST

atari_src/delay.c

@@ -0,0 +1,52 @@
+#include <stdio.h>
+#include <osbind.h>
+
+#define TIM_A_MFP 13
+#define TIM_A_XBIOS 0
+
+#define MFP_ISR_RUNNING_REG *((volatile unsigned char*)0xFFFFFA0FL)
+#define MFP_VECTOR_REG *((volatile unsigned char*)0xFFFFFA17L)
+
+#define ISR_RUNNING_TIM_A 0x20
+#define VECTREG_SW_EOI 0x08
+
+volatile unsigned int ticks = 0;
+
+static void __attribute__((interrupt)) tim_a_isr(void) {
+	ticks++;
+	// Notify MFP of end-of-interrupt bc we're in
+	// sw eoi mode
+	MFP_ISR_RUNNING_REG &= ~ISR_RUNNING_TIM_A;
+}
+
+static void tim_a_set_sei( void ) {
+	// Set software end-of-interrupt mode
+	MFP_VECTOR_REG |= VECTREG_SW_EOI;	
+}
+
+void delay_ms(unsigned int delay) {
+	// Disable the timer int if it was enabled
+	Jdisint(TIM_A_MFP);
+	
+	// reset elapsed ticks
+	ticks = 0;
+
+	// Initialize Timer A (for user progs)
+	// Set Prescaler to 50 and counter start to 50
+	// 50/(2.4576MHz) * 50 is approx 1ms
+	// Set ISR to our handler
+	Xbtimer(TIM_A_XBIOS, 4, 50, tim_a_isr);
+	
+	// NOt sure if this is 100% necessary or Xbtimer
+	// always takes care of this. In any case, here
+	// we set software EOI mode and enable the Timer A
+	// interrupt
+	Supexec(tim_a_set_sei);
+	Jenabint(TIM_A_MFP);
+
+	// Wait until delay ms have elapsed
+	while(ticks < delay);
+	// Disable the interrupt again
+	Jdisint(TIM_A_MFP);
+}
+