Git-Mirrors/OpenModem
1
0
Fork 0
mirror of https://github.com/markqvist/OpenModem.git synced 2024-10-01 03:15:46 -04:00
Code Issues Actions Packages Projects Releases Wiki Activity

Before AX.25 test

Browse Source
This commit is contained in:
Mark Qvist 2014-04-10 11:43:49 +02:00
parent 5452a7f662
commit aa59d254cd
1 changed files with 17 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

23
Modem/hardware.c
View File

@ -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);