Processor: AM3703CBP100
My symptom is that mcspi1_somi / gpio173 doesn't behave as I'd expect. When configured as mcspi1_somi, all signals on the SPI bus look correct when viewed on an oscilloscope, except the somi line swings from 0 volts to 0.6 volts rather than the full 0-1.8V. The padconf register 0x480021CC[15:0] reads 0x0100, so it is input enabled (as is mcspi1_clk). MCSPI_CHxCONF is 0x000103D5, so I believe that IS, DPE1 and DPE0 are set correctly (namely, somi selected for reception, transmission on simo, no transmission on somi).
If I disconnect the physical somi wire, the oscilloscope shows a full 1.8V swing, however, when connected, I get the 0-0.6V swing.
As an addition piece of information, if I reconfigure the padconf as 0x0004 (mode 4, gpio173, input and pulls disabled) and attempt to toggle the pin, I get a swing from 0V at logic low to 0.4V at logic high. This occurs with or without a physical wire connected, measuring at a header.
Doing the same to the simo pin (configured as gpio172) gives a full 0-1.8V output toggling from 0 to 1.
So, I don't know if something on the gumstix computer or development board is loading the line (they claim it's an unbuffered line straight to the processor) or if there's a subtle misconfiguration that I'm missing. Any ideas are greatly appreciated.