generate tachometer signal

1 files changed, 49 insertions, 0 deletions

diff --git a/fw/tests/system/tach_systest.c b/fw/tests/system/tach_systest.c
new file mode 100644
index 0000000..db65500
--- /dev/null
+++ b/fw/tests/system/tach_systest.c
@@ -0,0 +1,49 @@
+#include <xc.h>
+
+#include <stdint.h>
+
+#include "system.h"
+#include "types.h"
+
+// (pulse/min) = 60 * (Fosc/4) / ((pre)*(post)*(2^16 - TMR1))
+//  = 60 * (48e6/4) / (8*6*(2^16 - TMR1))
+//  = 15000000 / (2^16 - TMR1)
+#define TACH_FACTOR 15000000ul
+#define TMR1_POST 6u // TMR1 postscaler -- must be multiple of 2
+#define EDGE_PER_PULSE 2u // rising and falling edge
+
+static volatile U16 tmr1Start = 0u;
+
+void
+main(void) {
+	sysInit();
+
+	U16 pulsePerMin = 2500u;
+	tmr1Start = (((U32)1ul<<16u) - (U32)TACH_FACTOR / (U32)pulsePerMin) & 0xFFFF;
+
+	T1CON = 0x31; // source=Fosc/4, prescaler=1:8, enable=1
+
+	INTCON = 0x00;
+	PIE1bits.TMR1IE = 1;
+	INTCONbits.PEIE = 1;
+	INTCONbits.GIE = 1;
+
+	for (;;) {
+
+	}
+}
+
+void __interrupt()
+isr(void) {
+	static U8 tmr1Ctr = 0u;
+
+	if (TMR1IF) { // tachometer
+		if (++tmr1Ctr == (TMR1_POST/EDGE_PER_PULSE)) {
+			tmr1Ctr = 0u;
+			TACH_PIN ^= 1; // toggle tachometer output
+		}
+		TMR1H = (tmr1Start>>8u)&0xFF; // reset timer
+		TMR1L = (tmr1Start>>0u)&0xFF;
+		TMR1IF = 0;
+	}
+}