From aa59d254cd12b23d3316717d45f3cad9190ba13d Mon Sep 17 00:00:00 2001 From: Mark Qvist Date: Thu, 10 Apr 2014 11:43:49 +0200 Subject: [PATCH] Before AX.25 test --- Modem/hardware.c | 23 +++++++++++++++++------ 1 file changed, 17 insertions(+), 6 deletions(-) diff --git a/Modem/hardware.c b/Modem/hardware.c index 3b12fb7..2c835e8 100644 --- a/Modem/hardware.c +++ b/Modem/hardware.c @@ -19,7 +19,7 @@ static Afsk *modem; // M1 correction = 9500 // M2 correction = 40000 -#define FREQUENCY_CORRECTION 0 +#define FREQUENCY_CORRECTION 9500 // This function initializes the ADC and configures // it the way we need. @@ -43,18 +43,29 @@ void hw_afsk_adcInit(int ch, Afsk *_modem) // WGM13 and WGM12 together enables "Timer Mode 12", which // is Clear Timer on Compare, compare set to TOP, and the // source for the TOP value is ICR1 (Input Capture Register1). + // TOP means that we specify a maximum value for the timer, and + // once that value is reached, an interrupt will be triggered. + // The timer will then start from zero again. As just noted, + // the place we specify this value is in the ICR1 register. TCCR1A = 0; TCCR1B = BV(CS10) | BV(WGM13) | BV(WGM12); - // Then we set the ICR1 register to what count value we want to + // We now set the ICR1 register to what count value we want to // reset (and thus trigger the interrupt) at. - // Since the prescaler is set to 2MHz, the counter will be - // incremented two million times each second, and we want the - // interrupt to trigger 9600 time each second. The formula for + // Since the timer is running at 16MHz, the counter will be + // incremented 16 million times each second, and we want the + // interrupt to trigger 9600 times each second. The formula for // calculating the value of ICR1 (the TOP value) is: // (CPUClock / Prescaler) / desired frequency - 1 // So that's what well put in this register to set up our - // 9.6KHz sampling rate. + // 9.6KHz sampling rate. Note that we can also specify a clock + // correction to this calculation. If you measure your processors + // actual clock speed to 16.095MHz, define FREQUENCY_CORRECTION + // as 9500, and the actual sampling (and this modulation and + // demodulation) will be much closer to an actual 9600 Hz. + // No crystals are perfect though, and will also drift with + // temperature variations, but if you have a board with a + // crystal that is way off frequency, this can help alot. ICR1 = (((CPU_FREQ+FREQUENCY_CORRECTION)) / 9600) - 1; kprintf("ICR1=%d",ICR1);