Saturn: Use WDT for measuring elapsed time

src/saturn/Platform_Saturn.c

@@ -91,36 +91,31 @@ void DateTime_CurrentLocal(struct cc_datetime* t) {
 /*########################################################################################################################*
 *--------------------------------------------------------Stopwatch--------------------------------------------------------*
 *#########################################################################################################################*/
-static volatile cc_uint32 overflow_count, wdt_overflows;
+#include "sh2_wdt.h"
 
-static void wdt_handler(void) { wdt_overflows++; }
-static void ovf_handler(void) { overflow_count++; }
+static void Stopwatch_Init(void) {
+	wdt_stop();
+
+	wdt_set_irq_number(CPU_INTC_INTERRUPT_WDT_ITI);
+	wdt_set_irq_priority(15);
+    cpu_intc_ihr_set(CPU_INTC_INTERRUPT_WDT_ITI, wdt_handler);
+
+	wdt_enable();
+}
 
 cc_uint64 Stopwatch_Measure(void) {
-	return cpu_frt_count_get() | (overflow_count << 16);
+	return wdt_total_ticks();
 }
 
 #define US_PER_SEC     1000000
-#define NTSC_320_CLOCK 26846588
+#define NTSC_320_CLOCK 26846587
 
 cc_uint64 Stopwatch_ElapsedMicroseconds(cc_uint64 beg, cc_uint64 end) {
 	if (end < beg) return 0;
 	cc_uint64 delta = end - beg;
 
 	// TODO still wrong?? PAL detection ???
-	return (delta * US_PER_SEC) / (NTSC_320_CLOCK / 128);
-}
-
-static void Stopwatch_Init(void) {
-	//cpu_frt_init(CPU_FRT_CLOCK_DIV_8);
-	cpu_frt_init(CPU_FRT_CLOCK_DIV_128);
-	cpu_frt_ovi_set(ovf_handler);
-	cpu_frt_interrupt_priority_set(15);
-
-	//cpu_wdt_init(CPU_WDT_CLOCK_DIV_4096);
-	//cpu_wdt_interrupt_priority_set(15);
-	//cpu_wdt_timer_mode_set(CPU_WDT_MODE_INTERVAL, wdt_handler);
-	//cpu_wdt_enable();
+	return (delta * US_PER_SEC) / (NTSC_320_CLOCK / 1024);
 }
 
 

src/saturn/sh2_wdt.h

@@ -0,0 +1,73 @@
+static cc_uint32 wdt_overflows;
+
+// Interrupt Priority Request A
+#define SH2_REG_IPRA ((volatile uint16_t *)0xFFFFFEE2)
+#define SH2_IPRA_WDT_NUM 4
+
+// Vector Number Setting Register WDT
+#define SH2_REG_VCRWDT ((volatile uint16_t *)0xFFFFFEE4)
+#define SH2_VCRWDT_NUM 8
+
+// Watchdog Timer Counter
+#define SH2_REG_WTCNT_R	   ((volatile uint8_t  *)0xFFFFFE81)
+#define SH2_REG_WTCNT_W    ((volatile uint16_t *)0xFFFFFE80)
+#define SH2_CMD_WTCNT(val) (0x5A00 | (uint8_t)(val))
+
+// Watchdog Timer Control/Status Register
+#define SH2_REG_WTCSR_R	   ((volatile uint8_t  *)0xFFFFFE80)
+#define SH2_REG_WTCSR_W    ((volatile uint16_t *)0xFFFFFE80)
+#define SH2_CMD_WTCSR(val) (0xA500 | (uint8_t)(val))
+
+#define SH2_WTCSR_CLOCK_DIV_2    0
+#define SH2_WTCSR_CLOCK_DIV_64   1
+#define SH2_WTCSR_CLOCK_DIV_128  2
+#define SH2_WTCSR_CLOCK_DIV_256  3
+#define SH2_WTCSR_CLOCK_DIV_512  4
+#define SH2_WTCSR_CLOCK_DIV_1024 5
+#define SH2_WTCSR_CLOCK_DIV_4096 6
+#define SH2_WTCSR_CLOCK_DIV_8192 7
+
+#define SH2_WTCSR_ENA_FLG  0x20
+#define SH2_WTCSR_OVF_FLG  0x80
+
+
+static CC_INLINE void wdt_set_irq_number(int irq_num) {
+	uint16_t vcrwdt = *SH2_REG_VCRWDT;
+	vcrwdt &= ~(   0x7F << SH2_VCRWDT_NUM);
+	vcrwdt |=  (irq_num << SH2_VCRWDT_NUM);
+
+	*SH2_REG_VCRWDT = vcrwdt;
+}
+
+static CC_INLINE void wdt_set_irq_priority(uint8_t pri) {
+	uint16_t ipra = *SH2_REG_IPRA;
+	ipra &= ~(0xF << SH2_IPRA_WDT_NUM);
+	ipra |=  (pri << SH2_IPRA_WDT_NUM);
+
+	*SH2_REG_IPRA = ipra;
+}
+
+
+static void __interrupt_handler wdt_handler(void) {
+    uint8_t wtcr = *SH2_REG_WTCSR_R & ~SH2_WTCSR_OVF_FLG;
+
+    *SH2_REG_WTCSR_W = SH2_CMD_WTCSR(wtcr);
+    wdt_overflows++;
+}
+
+static CC_INLINE void wdt_stop(void) {
+	*SH2_REG_WTCSR_W = SH2_CMD_WTCSR(SH2_WTCSR_CLOCK_DIV_1024);
+}
+
+static CC_INLINE void wdt_enable(void) {
+	uint8_t wtcr = *SH2_REG_WTCSR_R & ~SH2_WTCSR_OVF_FLG;
+    wtcr |= SH2_WTCSR_ENA_FLG;
+	// interval mode is 0 anyways
+
+    *SH2_REG_WTCNT_W = SH2_CMD_WTCNT(0);
+	*SH2_REG_WTCSR_W = SH2_CMD_WTCSR(wtcr);
+}
+
+static CC_INLINE uint32_t wdt_total_ticks(void) {
+	return (*SH2_REG_WTCNT_R) | (wdt_overflows << 8);
+}