change prescaler to 1, frequency to 20Mhz

xukangmin · Jun 26, 2019 · 1d20807 · 1d20807
1 parent 424422c
commit 1d20807
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Showing 2 changed files with 32 additions and 11 deletions.
diff --git a/avr/cores/tiny/Arduino.h b/avr/cores/tiny/Arduino.h
@@ -78,7 +78,7 @@ void yield(void);
 #define interrupts() sei()
 #define noInterrupts() cli()
 
-#define PRESCALER 4
+#define PRESCALER 1
 
 #define CLK_PER F_CPU / PRESCALER // default prescaler 6, datasheet Page 78, MCLKCCTRLB to Change prescalar
 

diff --git a/avr/cores/tiny/wiring.c b/avr/cores/tiny/wiring.c
@@ -3,15 +3,17 @@
 
 #define TIMER0_TOP_VALUE 0xFF
 
-#define MICROSECONDS_PER_TIMER0_OVERFLOW (clockCyclesToMicroseconds(1 * TIMER0_TOP_VALUE))
+#define MICROSECONDS_PER_TIMER0_OVERFLOW (clockCyclesToMicroseconds(1 * 256))
 #define MILLIS_INC (MICROSECONDS_PER_TIMER0_OVERFLOW / 1000)
 
-#define FRACT_INC ((MICROSECONDS_PER_TIMER0_OVERFLOW % 1000) >> 3)
-#define FRACT_MAX (1000 >> 3)
+#define FRACT_INC 8   // calculated base on 12.8 microseoncds per time0 overflow // 256 / 20
+#define FRACT_MAX 625
+
+//#define MICROSECONDS_PER_TIMER0_OVERFLOW 12.8   // 256 / 20
 
 volatile unsigned long timer0_overflow_count = 0;
 volatile unsigned long timer0_millis = 0;
-static unsigned char timer0_fract = 0;
+static unsigned int timer0_fract = 0;
 
 static void __empty() {
 	// Empty
@@ -21,7 +23,7 @@ void yield(void) __attribute__ ((weak, alias("__empty")));
 ISR(TCA0_LUNF_vect)
 {
 	unsigned long m = timer0_millis;
-	unsigned char f = timer0_fract;
+	unsigned int f = timer0_fract;
 
 	m += MILLIS_INC;
 	f += FRACT_INC;
@@ -82,13 +84,32 @@ void delay(unsigned long ms)
 
 void delayMicroseconds(unsigned int us)
 {
+
+
+	// __asm__ __volatile__ (
+	// "nop" "\n\t"
+	// "nop" "\n\t"
+	// "nop" "\n\t"
+	// "nop"); //just waiting 4 cycles
+	if (us <= 1) return; //  = 3 cycles, (4 when true)
+
+	// the following loop takes a 1/5 of a microsecond (4 cycles)
+	// per iteration, so execute it five times for each microsecond of
+	// delay requested.
+	us += (us << 1); // x5 us, = 7 cycles
+
+	// account for the time taken in the preceeding commands.
+	// we just burned 26 (28) cycles above, remove 7, (7*4=28)
+	// us is at least 10 so we can substract 7
+	us -= 7; // 2 cycles
+
 	// F_CPU = 5Mhz
 
-	if (us <= 10) return;
+	// if (us <= 10) return;
 
-	us += us >> 3; // us * 1.125
+	// us += us >> 3; // us * 1.125
 
-	us >>= 1;  // div / 2
+	// us >>= 1;  // div / 2
 
 	__asm__ __volatile__ (
 	"1: sbiw %0,1" "\n\t" // 2 cycles
@@ -100,9 +121,9 @@ void init(void)
 {
   CCP = CCP_IOREG_gc; // enable write protect
 
-  CLKCTRL_MCLKCTRLB = (1 << CLKCTRL_PDIV0_bp) | (1 << CLKCTRL_PEN_bp); // change prescalar to 4, so it's 20Mhz/4 = 5MHz
+  //CLKCTRL_MCLKCTRLB = (1 << CLKCTRL_PDIV0_bp) | (1 << CLKCTRL_PEN_bp); // change prescalar to 4, so it's 20Mhz/4 = 5MHz
 
-  //CLKCTRL_MCLKCTRLB = 0x00;
+  CLKCTRL_MCLKCTRLB = 0x00;
 
   SREG |= (1 << CPU_I_bp); // global enable interrupt