Fix CAN.begin() for MCP2515 with 8 MHz quartz by increasing the delay

[timurrrr]

Hi!

I bought a few MCP2515 from Amazon and they all came with 8 MHz quartz crystal. Whenever I called CAN.begin(), it would return 0. I was sure I set all the configuration parameters correctly before calling it.

It took me some time to debug, but then I started reading the datasheet [1] and found section 8.1 that says

8.1 Oscillator Start-up Timer
The MCP2515 utilizes an Oscillator Start-up Timer
(OST) that holds the MCP2515 in Reset to ensure that
the oscillator has stabilized before the internal state
machine begins to operate. The OST keeps the device
in a Reset state for 128 OSC1 clock cycles after the
occurrence of a Power-on Reset, SPI Reset, after the
assertion of the RESET pin, and after a wake-up from
Sleep mode. It should be noted that no SPI protocol
operations should be attempted until after the OST has
expired.

There is a delayMicroseconds(10); inside MCP2515Class::reset(), but some quick math reveals that 128 clock cycles of a 8 MHz clock is 16 microseconds. Indeed, changing the value from 10 to 16 makes CAN.begin() work for me.

[1] http://ww1.microchip.com/downloads/en/DeviceDoc/MCP2515-Stand-Alone-CAN-Controller-with-SPI-20001801J.pdf

[utkarshsethi]

Is this not solved by #set-clock-frequency?