FSK with SAMD21 10 bits DAC through DMA

The design converges toward a SAMD21 triggered by an IRQ from the 1 PPS signal. Time and date will be FSK encoded through direct digital synthesis in the MCU. F1 and F2 will be 1200 and 2200 Hz (as in Bell 202 modem). Demodulation will be done on the desktop.