Keith Emery wrote:
When I enable spkmodem in the coreboot config, I get output from the PC speaker. But spkmodem-recv interprets the tones as consistent gibberish. The output is consistent with a mismatch in the baud rates, but there appears no apparent way to select anything different in the spkmodem-recv software.
spkmodem uses a fixed baudrate, IIRC 1200.
Did you look at a recording in a spectrum analyzer software? Maybe that would help identify modulation timing issues.
If the CPU is running coreboot as fast as possible while receiving those instructions from a relatively slow SPI bus. Is it possible that I've somehow overclocked the SPI bus, leading to a mismatch in the baud rates?
SPI isn't involved in tone timing, I think only the (emulated) legacy timer is used for that.
//Peter