I need to select a System on Module that will be used to stream a HD video stream over WIFI. Ideally it should support two camera input.
When researching the various modules on the market, I find some SOCs exposing either Camera Serial Interface (CSI) or Camera Parallel Interface (CPI), or both.
I understand CSI is newer (and I assume 'better', but in which terms ?). Thus, from a system architecture standpoint, when should someone choose CSI over CPI ? Or the opposite ?
You should go with CSI-capable SoMs when possible. As jippie said, parallel interface adds a variety of issues that can result in reduced performance. In addition, some SoMs (iMX6 Quad) have CSI inputs that have the bandwidth to support more than one camera, provided they are multiplexed properly.
Make sure to take a close look at any SoM datasheets before committing to ensure they have the interface you want, as parallel interfaces sometimes get the CSI label and can cause confusion.
Parallel is older, but perhaps a little easier to understand and interface to. Serial is an attempt to go faster, ie more data higher resolution, use less pins, and less power. Some sensors come with both modes, also most of the serial interfaces I've seen are under NDA.
So your application will determine the right choice, as will what you want to use as a controller.
