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In MCP2515::ReadBuffer(), message.extended is set by a bit mask (byte2 & B00001000)

Because CAN_FRAME flags are uint8's, the value '8' is stored, and eventually printed into log files in M2RET, confusing savvyCAN which doesn't interpret the 8 as being true.

I'm sure there's a good reason for this, but why aren't the flags in CAN_FRAME defined as bool?
In any case, this can probably be fixed by casting the bit mask result to a bool before assigning it. We should probably do the same for RTR.

Copy pasted the code exactly to play with and i get these errors. I know it's an old library, but has something changed?

sketch_oct28a:44:1: error: 'Frame' does not name a type
 Frame testMessage;
 ^
C:\Projects\sketch_oct28a\sketch_oct28a.ino: In function 'void setup()':
sketch_oct28a:90:32: error: no matching function for call to 'MCP2515::SetRXMask(int, int, int)'
   CAN.SetRXMask(MASK0, 0x7F8, 0); //match all but bottom four bits
                                ^
In file included from C:\Projects\sketch_oct28a\sketch_oct28a.ino:26:0:
C:\Users\ec\Documents\Arduino\libraries\mcp2515-master\src/MCP2515.h:85:7: note: candidate: void MCP2515::SetRXMask(uint8_t, uint32_t)
  void SetRXMask(uint8_t mask, uint32_t MaskValue);
       ^
C:\Users\ec\Documents\Arduino\libraries\mcp2515-master\src/MCP2515.h:85:7: note:   candidate expects 2 arguments, 3 provided
sketch_oct28a:100:7: error: 'testMessage' was not declared in this scope
       testMessage.id = 0x07DF;
       ^
C:\Projects\sketch_oct28a\sketch_oct28a.ino: At global scope:
sketch_oct28a:114:1: error: 'Frame' does not name a type
 Frame message;
 ^
C:\Projects\sketch_oct28a\sketch_oct28a.ino: In function 'void loop()':
sketch_oct28a:117:22: error: 'message' was not declared in this scope
   if (CAN.GetRXFrame(message)) {
                      ^
sketch_oct28a:31:20: error: 'LED_BUILTIN' was not declared in this scope
 #define LED_CAN_TX LED_BUILTIN
                    ^
C:\Projects\sketch_oct28a\sketch_oct28a.ino:144:32: note: in expansion of macro 'LED_CAN_TX'
                   digitalWrite(LED_CAN_TX, txLEDState);
                                ^
exit status 1
'Frame' does not name a type

This is the only bit of code that I have come across that I know to be targeting the Macchina v1.1 and I know there was some discussion about moving this under the macchina GitHub organization. Asking to know whether it should be clarified this is for an older Macchina product.

If MCP2515::intHandler() is called from an actual interrupt handler while another SPI transfer is in progress, it will try to initiate another SPI transfer, causing one or both transfers to fail.

There are two ways to work around this in client code:

1. Surround every call to sendFrame(), Mode(), SetRXFilter(), etc. with noInterrupts()/interrupts()
2. Do nothing except set a flag in the actual interrupt handler, then call MCP2515::intHandler later.

The first method works for me because I am not using any other SPI devices on the bus. If I were, then I would have to also disable interrupts for those operations. The second method works best if the flag can be polled frequently, otherwise received frames might get lost.

I'm not sure what the best solution would be for fixing the library, though.

void MCP2515::SetRXMask(uint8_t mask, uint32_t MaskValue, bool ext)

and

void MCP2515::SetRXFilter(uint8_t filter, uint32_t FilterValue, bool ext)

I could not get filters to work without this change.