Check the xCORE-200 Devices Portmap document - http://www.xmos.com/published/xcore-200-devices-portmap
You can see the XU208 leaves 9 x 1b ports after USB is turned on (columns S to V).
For USB audio to I2S you need the following 1b ports:
1 data line per 2 channels per direction
For USB to TDM you need:
1 data line per 8 channels per direction
You also need:
4 x 1b ports for SPI flash
2 x 1b ports for QSPI flash (data is handled on 4b port)
Luckily I2C can be handled on a 4b port so any config can be done without consuming 1b ports.
Let's assume using QSPI (or device with integrated flash which internally is QSPI). So you have:
9 - 3 - 2 = 4 data lines available for audio. So that will easily support 6 channels output with a spare 1b port for I2S or 3 data lines if you choose TDM. You could also re-use the QSPI QSCLK after boot time as an output (eg. BCLK) if you are careful with board layout, which claws back another 1b port.
Note this is a straight n channel USB to I2S bridge which transports bit perfect samples across. There is no 'decode' of multichannel - it is assumed that is done on the host.
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