In order to evaluate more than one SigmaDSP at a time without the need for creating special prototype hardware, the USBi can be modified to connect with more than one evaluation board. In this example, a single USBi connects to two evaluation boards: the ADAU1781 and ADAU1761.
First of all, the USBi needs to be modified to add an extra connector to its ribbon cable. The connector simply crimps onto the existing cable and requires no soldering at all - the only tool I used was a vice to make sure the connection was tight. The part number on Digikey is MKC10K-ND, and the description is SOCK CONN 10 CONT OPEN W/POL GLD. The connector should be added to the ribbon cable with the same orientation (and by extension, pinout) as the existing 10-pin connector.
The following picture shows the basic setup. An MP3 player is used as an audio source. It feeds analog audio into the ADAU1761. The audio passes through the ADAU1761's ADCs and SigmaDSP core and then is output on the serial port to the ADAU1781 board. The ADAU1781 takes the audio in through its serial port, through its SigmaDSP core, and then outputs it through the DAC to the headphones.
NOTE: Clicking on the pictures in this post will increase their size.
The ADAU1781 board is the clock master, running off of its on-bard oscillator. It sends a master clock, LRCLK, and BCLK over to the ADAU1761 board, and receives data back from the ADAU1761's serial port. The connections were made here with simple fly-wires. Because the signals are somewhat high frequency (12.288 MHz for MCLK), the wires should be kept as short as possible to maintain signal integrity.
This picture shows the corresponding connections for the flywires on the ADAU1761 side.
The ADAU1781 and ADAU1761 boards will have the same I2C address by default. This needs to be modified in order to let the USBi differentiate between the two devices. Simply moving a resitor on the bottom of the ADAU1781 board will accomplish this goal.
The jumper/switch settings of the ADAU1781 board are shown here.
The jumper/switch settings of the ADAU1761 board are shown here.
In SigmaStudio, the USBi should be set up to communicate with the ADAU1781 and ADAU1761 on separate addresses, corresponding with the addresses used on the evaluation boards.
My basic audio flow has audio in from the ADAU1761 ADCs and out as I2S, then in as I2S to the ADAU1781 and out to its DACs. Of course, processing can be added here in SigmaStudio as necessary.
A working example project file is attached.