improve layer switching

timer.c

@@ -0,0 +1,61 @@
+#include <avr/io.h>
+#include <avr/interrupt.h>
+#include <stdint.h>
+#include "timer.h"
+
+uint16_t timer_count = 0;
+
+// Configure timer 0 to generate a timer overflow interrupt every
+// 256*1024 clock cycles, or approx 61 Hz when using 16 MHz clock
+// This demonstrates how to use interrupts to implement a simple
+// inactivity timeout.
+void timer_init(void)
+{
+    TCCR0A = 0x00;
+    TCCR0B = 0x05;
+    TIMSK0 = (1<<TOIE0);
+}
+
+inline
+void timer_clear(void)
+{
+    cli();
+    timer_count = 0;
+    sei();
+}
+
+inline
+uint16_t timer_read(void)
+{
+    uint8_t _sreg = SREG;
+    uint16_t t;
+
+    cli();
+    t = timer_count;
+    SREG = _sreg;
+
+    return t;
+}
+
+inline
+uint16_t timer_elapsed(uint16_t last)
+{
+    uint8_t _sreg = SREG;
+    uint16_t t;
+
+    cli();
+    t = timer_count;
+    SREG = _sreg;
+
+    return TIMER_DIFF(t, last);
+}
+
+// This interrupt routine is run approx 61 times per second.
+// A very simple inactivity timeout is implemented, where we
+// will send a space character and print a message to the
+// hid_listen debug message window.
+ISR(TIMER0_OVF_vect)
+{
+    timer_count++;
+}
+