Add global timer

src/arch/8051/time.c

@@ -0,0 +1,41 @@
+// Uses timer 0 to keep track of global time
+
+#include <8051.h>
+#include <stdint.h>
+
+#include <arch/time.h>
+
+static volatile uint32_t time_overflows = 0;
+
+void timer_0(void) __interrupt(1) {
+    time_overflows++;
+    
+    // Restart timer
+    TR0 = 0;
+    TF0 = 0;
+    TH0 = 0xFD;
+    TL0 = 0x01;
+    TR0 = 1;
+}
+
+void time_init(void) __critical {
+    // Stop the timer
+    TR0 = 0;
+    TF0 = 0;
+
+    time_overflows = 0;
+
+    // Enable timer interrupts
+    ET0 = 1;
+
+    // Start timer in mode 1
+    // (65536 - 64769) / (9.2 MHz / 12) = ~1 ms interval
+    TMOD = (TMOD & 0xF0) | 0x01;
+    TH0 = 0xFD;
+    TL0 = 0x01;
+    TR0 = 1;
+}
+
+uint32_t time_get(void) __critical {
+    return time_overflows;
+}