change SERCOM clock to 3.3 MHz
we use the SERCOM peripheral for USART (in 7816 mode SIM card
communication) in synchronous mode (TX and RX clock are the same).
in this mode only the 8 least significant bits of the BAUD register
are used (see TRM 33.6.2.3 Clock Generation – Baud-Rate Generator).
When the SERCOM is clocked at 100 MHz the minimum resulting baud
rate would be 100E6 / (2 * 255 + 1) = 195694 bps.
clocking SERCOM at 3.33 MHz also to have a baud rate of 6720 bps
(~ 3.33E6 / (2 * 247 + 1)), used after reset to read the ATR.
Change-Id: Id60322e092a6652a89821fc737d5336d79a1420c
2 files changed