The MPC5200 is a very powerful and versatile chip. It runs at better than 500MHz. It has an integrated FPU. It is well supported in Linux. It has a rich set of peripherals (UART, Ethernet, USB, I2C, I2S, ...etc). Unfortunately, as an audio processor, it has one serious flaw. The I2S interfaces can not be clocked at common audio frequencies using the internal clock. This means that any quality audio design using the MPC5200 requires an external clocking source.

The addition of an accurate external clock does not disqualify the MPC5200 as an audio processor. It is still very powerful and versatile. For instance, the FPU can be used to encode/decode audio files without really taxing the CPU. But, the MPC5200 is a little expensive compared with other chips that can be used for audio processing. The MPC5200 is about $18 in 1000 quantity. The addition of an external audio chip (with crystal and glue) will add another $2+ to the design. That adds up to $20 of cost just for the CPU.

By comparison, the Cirrus EP9302 is a $10 chip (in 1000 quantities) that has the ability to accurately produce all the common audio frequencies. That is half the price of the MPC5200 and translates into a $30 to $50 savings on the retail price. That is a significant percentage (10%) of the target price of a DigiSpeaker node (~$500 at this time).

For certain, the Cirrus EP9302 is far less powerful than the MPC5200. It is an ARM9 chip with an integrated FPU that runs at 200MHz. Decoding compressed audio files will take up a significant portion of the available CPU cycles. However, representatives of the company assure us that it can keep up with audio decodes and still have cycles left for other tasks (user interface, file read/write, network, ..etc). The EP9302 probably is not powerful enough to encode audio files, but that is not required of most DigiSpeaker nodes. The few nodes that do require audio I/O (we predict one to two per house) can be constructed with the MPC5200 driven by clocks sourced from the I/O module itself (the very accurate Wolfson WM8580).

At this time, the MPC5200 is our primary choice. However, we have purchased evaluation boards for the EP9302 to do some experimentation. The results of those experiments will tell us which CPU to use going forward.