BCM2835_I2S_RXON
off |= rx ? BCM2835_I2S_RXON : 0;
i2s_active_state = csreg & (BCM2835_I2S_RXON | BCM2835_I2S_TXON);
BCM2835_I2S_RXON | BCM2835_I2S_TXON, i2s_active_state);
if (csreg & (BCM2835_I2S_TXON | BCM2835_I2S_RXON))
mask = BCM2835_I2S_RXON;
mask = BCM2835_I2S_RXON;