High-Resolution Low-Jitter GPIO Clock on BBB?


There are several interesting projects using the Raspberry Pi (FM transmitter, WSPR Beacon, SSB Transmitter) to generate RF via one of the BCM2835’s programmable clocks that is exposed on the RPi header, GPIO4. Through clever use of the BCM2835’s MASH filter to produce an average frequency, and DMA code to toggle between two frequencies, these projects are able to generate frequencies with 1.5 Hz resolution up into the FM (108 MHz) range. Even without use of the clever DMA code, one can program these clocks with fractional dividers in resolutions of <=20 kHz up to at least 120 MHz. I would like to try a similar project on the BBB. Are there any similar clocks in the AM335x and exposed by the BBB? More specifically, is there any way to synthesize a clock in the range of 1 to 120 MHz with resolution of at least 20 kHz at the high frequency end for use by a cape? If so, are there code examples?


Steve Haynal