[tmzt]

There's also the possibility of reprogramming a PINMUX to move access from the AP to the BP on the same SoC for something like SPI.

Essentially, most of the pins on the SoC are re-programmable to have different functions or connect to different logical blocks within the SoC.

Along these lines there's also bit-banging SPI or I2C, which should work fine for infrequent updates from an accel or compass (and now things like pedometers being added to devices.)

As for microphone, if it's being read by the audio DSP, it's certainly accessible from the baseband, at least on Qualcomm . If nothing else you can load a DSP module that allows access to the raw PCM (or vocoder) data.

Same is probably true for the camera, which is usually on an HSIF or similar bus connected to the DSP.