pico-tracker/firmware/Peripherals.md

SAM D20 Peripherals usage

Type	Peripheral	Function	Notes
GLCK
	gclk0	main clock, internal osc8m	4 MHz
	gclk1	tcxo clock, fed from xosc OR osc8m
	gclk7	aprs clock, fed from gclk1, div 6 / 11
TC
	tc0	telemetry tick timer. 32-bit. glck1
	tc1	^^^^^
	tc2	counts cycles of tcxo. 32-bit. gclk1
	tc3	^^^^^
	tc4	unused (osc8m event source)
	tc5	telemetry pwm 16-bit glck0, ALSO aprs carrier 16-bit gclk7
EXTINT
	extint[5]	gps timepulse
event channels
	0	event source for timer 2 xosc measurement
	1	tc4 retrigger
SERCOM
	sercom0	spi flash
	sercom1	ublox gps
	sercom2
	sercom3	radio	currently bitbanged as required pin layout broken in sercom

SAM D20 Interrupts usage

Name	Function	Priority H(0-3)L	Notes
TC0_IRQn	telemetry tick timer	1	latency critical for symbol timing. rate <= 1200Hz
[GPS_SERCOM]_IRQn	gps usart rx	2	latency not so critical. rate <= 960Hz
EIC_IRQn	timepulse	3	latency not so critical. rate = 1
TC2_IRQn	xosc measurement done	3	latency not critical
ADC_IRQn	adc measurement done	3	latency not critical

Clock Layout

[osc8m] --> [glck0] +--> [gps usart]
                    |--> [tc5]
                    |--> [adc]
                    |--> [extint]
                    |--> [cm0+, apbs etc.]


                     |\
         [osc8m]--> 0| |
                     | | --> [glck1] +--> [tc0, telemetry tick]
tcxo --> [xosc] --> 1| |             |--> [tc2, count tcxo] <-- gps timepulse
                     |/              |--> [glck7] --> [tc5] --> si_gpio1
                      |
                 *USE_XOSC*


[osculp32k] --> [gclk4] --> [wdt]