In Sigma-Delta devices the SDO line is also used as an interrupt. Leaving IRQ on level instead of falling might trigger a sample read when the IRQ is enabled, as the SDO line is already low. Not sure if SDO line will always imediately go high in ad_sd_buffer_postenable before the IRQ is enabled. Also the datasheets seem to explicitly say the falling edge of the SDO should be used as an interrupt. -Alexandru
