tree 5ca52c94f19a0eec8934bef603eb48c9e2b91a62
parent f53d366c1d3daa0f5ac88af7b8a1ce53a5018a2c
author Kévin Redon <kredon@sysmocom.de> 1556200230 +0200
committer Kévin Redon <kredon@sysmocom.de> 1557409598 +0200

configure GCLK for ISO baud rates

the SERCOMM clock triplet 0.5 MHz (100 MHz / 200),
7.0588 MHz (120 MHz / 17), and 50 MHz (100 MHz / 2) allows to
generate all possible ISO 7816 baud rates (from
F = 2048 / D = 1 @ f = 2.5 MHz -> 1220 bps to
F = 372 / D = 64 @ f = 20 MHz -> 3.4 Mbps) with a maximum baud
rate error of 2.57 %, for available SIM clocks 2.5, 5, 10, 20 MHz.
2.57% means a bit more than quarter a bit might be wrong after the
11 bits ISO transmission (still less than half a bit).
This triplet is one of the optimum when 3 clocks are used.
An additional clock would be required for higher accuracy.

The 50 MHz clock is re-used from the RMII clock output.

Change-Id: I2c69848582e49031fa6453f535a2bf1408f8e22e