An AVR implementation in progress.

• ATmega328P running at 16MHz (Arduino Nano + Duemilanove)

• SPI configured in mode 0 (CPOL=0, CPHA=0) with prescaler 16 (SPR1=0, SPR0=1, SPI2X=0), resulting in 1MHz SPI speed. According to the data sheet, SPI rate during FIFO access must be smaller than 2.5MHz with the default 10MHz oscillator in place:

  Note: During FIFO access fSCK cannot be higher than fref /4, where f ref is the crystal oscillator frequency.

  A substantially lower SPI rate (i.e. lower than transmit frequency) results in buffer underruns on the transmitter side (RGUR in Status Register), obviously.

Wiring is basically as follows, although I eventually decided to invest in one of JeeLabs' RFM12B breakout boards.

From an early demo, leaving the power amplifier enabled for a second before and after transmission.

Later, the 47th transmission of HOLYCOW prefixed by magic pattern 0x01020304 (payload size 8).