Reduce CPU frequency

Also reduces PWM frequency. The speakers resonance frequency is 2kHz, with 1MHz
clock speed and prescaler 256 we get pretty close.

6 files changed, 53 insertions, 45 deletions

diff --git a/accel.c b/accel.c
index 9f38e8e..77126d4 100644
--- a/accel.c
+++ b/accel.c
@@ -163,22 +163,20 @@ bool accelProcess () {
 	if (reading && shouldWakeup (WAKE_I2C)) {
 		disableWakeup (WAKE_I2C);
 		reading = false;
-		if (twr.status == TWST_OK) {
-			accelProcessHorizon ();
-
-			/* calculate normalized z (i.e. without earth gravity component) */
-			if (horizonSign == HORIZON_NEG) {
-				zvalnormal = zval - (-ACCEL_1G);
-			} else if (horizonSign == HORIZON_POS) {
-				zvalnormal = zval - ACCEL_1G;
-			}
-
-			accelProcessShake ();
-			/* new data transfered */
-			return true;
-		} else if (twr.status == TWST_ERR) {
-			assert (0);
+		/* the bus might be in use again already */
+		//assert (twr.status == TWST_OK);
+		accelProcessHorizon ();
+
+		/* calculate normalized z (i.e. without earth gravity component) */
+		if (horizonSign == HORIZON_NEG) {
+			zvalnormal = zval - (-ACCEL_1G);
+		} else if (horizonSign == HORIZON_POS) {
+			zvalnormal = zval - ACCEL_1G;
 		}
+
+		accelProcessShake ();
+		/* new data transfered */
+		return true;
 	} else {
 		if (shouldWakeup (WAKE_ACCEL) && twr.status == TWST_OK) {
 			/* new data available in device buffer and bus is free */
diff --git a/common.h b/common.h
index 42737eb..5730f47 100644
--- a/common.h
+++ b/common.h
@@ -2,7 +2,7 @@
 #define COMMON_H
 
 /* cpu runs at n mhz */
-#define F_CPU 8000000
+#define F_CPU 1000000
 
 #define sleepwhile(cond) \
 	sleep_enable (); \
diff --git a/gyro.c b/gyro.c
index 3079c20..5b32314 100644
--- a/gyro.c
+++ b/gyro.c
@@ -136,16 +136,15 @@ bool gyroProcess () {
 			if (shouldWakeup (WAKE_I2C)) {
 				disableWakeup (WAKE_I2C);
 				state = IDLE;
-				assert (twr.status != TWST_ERR);
-				if (twr.status == TWST_OK) {
-					/* new data transfered, process it */
-					/* poor man's noise filter */
-					if (abs (zval) > 64) {
-						zaccum += zval;
-					}
-					gyroProcessTicks ();
-					return true;
+				/* the bus might be in use again already */
+				//assert (twr.status == TWST_OK);
+				/* new data transfered, process it */
+				/* poor man's noise filter */
+				if (abs (zval) > 64) {
+					zaccum += zval;
 				}
+				gyroProcessTicks ();
+				return true;
 			}
 			break;
 
diff --git a/i2c.c b/i2c.c
index 54e1f29..5505632 100644
--- a/i2c.c
+++ b/i2c.c
@@ -47,17 +47,20 @@ static bool twWriteRaw (const uint8_t data) {
 
 void twInit () {
 #if F_CPU == 1000000
-	/* set scl to 3.6 kHz */
+	/* set scl to 50 kHz */
 	TWBR = 2;
-	TWSR |= 0x3; /* set prescaler to 64 */
+	/* prescaler 1 */
+	TWSR &= ~((1 << TWPS1) | (1 << TWPS0));
 #elif F_CPU == 4000000
 	/* set scl to 50 kHz ? */
 	TWBR = 32;
-	TWSR |= 0x0; /* set prescaler to 0 */
+	/* prescaler 1 */
+	TWSR &= ~((1 << TWPS1) | (1 << TWPS0));
 #elif F_CPU == 8000000
 	/* set scl to 100 kHz */
 	TWBR = 32;
-	TWSR |= 0x0; /* set prescaler to 0 */
+	/* prescaler 1 */
+	TWSR &= ~((1 << TWPS1) | (1 << TWPS0));
 #else
 #error "cpu speed not supported"
 #endif
@@ -135,6 +138,8 @@ static void twIntWrite () {
 			if (TW_STATUS == TW_MT_DATA_ACK) {
 				twStopRaw ();
 				twr.status = TWST_OK;
+				enableWakeup (WAKE_I2C);
+				++twr.step;
 			} else {
 				twr.status = TWST_ERR;
 			}
@@ -232,6 +237,8 @@ static void twIntRead () {
 			if (status == TW_MR_DATA_NACK) {
 				twStopRaw ();
 				twr.status = TWST_OK;
+				enableWakeup (WAKE_I2C);
+				++twr.step;
 			} else {
 				twr.status = TWST_ERR;
 				twr.error = status;
@@ -258,8 +265,6 @@ ISR(TWI_vect) {
 			assert (0 && "nope\n");
 			break;
 	}
-	if (twr.status == TWST_ERR || twr.status == TWST_OK) {
-		enableWakeup (WAKE_I2C);
-	}
+	assert (twr.status != TWST_ERR);
 }
 
diff --git a/pwm.c b/pwm.c
index 250e489..0c9e191 100644
--- a/pwm.c
+++ b/pwm.c
@@ -79,8 +79,8 @@ void pwmStart () {
 	TIMSK0 = (1 << OCIE0A);
 	/* compare value */
 	OCR0A = 1;
-	/* io clock with prescaler 64; ctc (part 2) */
-	TCCR0B = (1 << CS02) | (0 << CS01) | (1 << CS00);
+	/* io clock with prescaler 256; ctc (part 2) */
+	TCCR0B = (1 << CS02) | (0 << CS01) | (0 << CS00);
 }
 
 void pwmStop () {
diff --git a/timer.c b/timer.c
index 0ca3586..bd2ed1e 100644
--- a/timer.c
+++ b/timer.c
@@ -5,10 +5,22 @@
 
 #include "timer.h"
 
-/* useconds per clock tick */
+/* prescaler is 1024 */
+#define PRESCALER ((1 << CS12) | (1 << CS10))
+
+#if F_CPU == 1000000
+/* with divider 1024 each tick is 1024us */
+#define US_PER_TICK 1024
+#define MAX_US ((uint32_t) 67107840)
+#elif F_CPU == 8000000
+/* with divider 1024 each clock tick is 128us with a rounding error of 64us
+ * per second/4ms per minute, since it’s a 16 bit timer we support up to
+ * 2**16-1 ticks, which is 8388480us (8s) */
 #define US_PER_TICK 128
-/* max useconds with max OCRA1 */
 #define MAX_US ((uint32_t) 8388480)
+#else
+#error "cpu speed not supported"
+#endif
 
 /* max/current timer hits */
 static volatile uint8_t maxhits, hits;
@@ -66,10 +78,6 @@ void timerStart (const uint32_t t, const bool once) {
 	/* enable compare match interrupt */
 	TIMSK1 = (1 << OCIE1A);
 	/* set compare value */
-#if F_CPU == 8000000
-	/* with divider 1024 each clock tick is 128us with a rounding error of 64us
-	 * per second/4ms per minute, since it’s a 16 bit timer we support up to
-	 * 2**16-1 ticks, which is 8388480us (8s) */
 	if (t >= MAX_US) {
 		maxhits = t/MAX_US+1;
 		count = UINT16_MAX;
@@ -82,11 +90,9 @@ void timerStart (const uint32_t t, const bool once) {
 		lastcount = tdiv;
 		OCR1A = tdiv;
 	}
-#else
-#error "cpu speed not supported"
-#endif
-	/* io clock with 1024 prescaler; ctc (part 2) */
-	TCCR1B = (1 << CS12) | (1 << CS10) | (1 << WGM12);
+
+	/* prescaler and ctc (part 2) */
+	TCCR1B = PRESCALER | (1 << WGM12);
 }
 
 void timerStop () {