xspi-bus

Aims:
1. To define a standard Serial Peripheral Interface expansion-bus to XMOS technology. To enable common operation among boards adopting the XSPI-bus design.
2. To support plug-and-play applications. By setting the XC-1 to boot-from-SPI and plugging an XSPI-board with bootable code resident in XSPI-device0 (i.e. a FLASH) into the XSPI-header on the XC-1, the embedded application executes after power-up.