The datasheet doesn't seem to provide any information on using an external reference clock for the SysTick clock source in the SAML21 processor. Can anybody provide clarity on how to use the external reference clock option in the control register for SysTick? Does it work? Which clock source does it use in this case?
According to the ARM spec, it would not allow me to clear the Clock Source control bit if it were not implemented. However, I am able to clear and read back a bit value of 0, indicating that it accepted the configuration for an external reference source. Unfortunately, I cannot find any information in the documentation (Microchip, Atmel, or ARM) about which clock source it uses as an external reference clock.