Turning on the SPI Engine communication with the CAN controller

With the firmware organization figured out we start to cobble together the first pieces of code which others have developed for us to test and learn from. In this case I'm starting with the SPI Engine 1.0. If you remember from the first post where I show which lines are probed you know that I've probed the SPI bus and a few extra lines to/from the CAN Controller. The logic analyzer capture (double click to enlarge) shows many bytes being sent to the MCP 2515 which include commands for toggling the /Rx0Bf, Rx1Bf, and /Int lines so we can see that the lines assert when the MCP 2515 wants to signal the Propeller that it needs servicing.

From top down the diagram shows the following signals:

• /Rx0BF
• /Rx1BF
• /INT
• SPI CLK
• SPI data to CAN
• SPI data from CAN
• /CS
• /Reset
• (the remainder can be ignored.)

A quick key to reading this is when the violet line is low (/CS asserted) we are commanding or reading data from the MCP 2515. The dark-red line is data from the propeller to the CAN device, while the dark-green line is data coming from the CAN device. At the top in bright red/yellow/green are the handshake lines coming from the CAN controller which when controlled by the MCP 2515 means something specific. In this test however I've set them up as general purpose I/O so I can toggle them and prove them to be working.

I'm seeing expected wiggles on all the right lines so for now (many software iterations to get to this point) we are having a great day!