This project describes the AD9911 Direct Digital Synthesizer. It is capable of generating a sine-wave between 250Mhz and >1Hz. The created evaluation unit is descripted here.
channel 1 is connected to the DAC. all aux channels are capable of modulating channel 1.
2-wire SPI mode, SDIO_0 is bidirectional !
you can write to multiple channels at once !
I've created a simple programm that runs on teensy 2.0 (ATMEGA32U4). It should run on any ATmega, just change the I/O ports.
Timings are not critical, as the ATmega is much slower than the maximum I/O updaterate of the AD9911.