Incorrect rtrBit checking in MCP_CAN::mcp2515_read_canMsg() method implementation

[sfyang]

Under current implementation, the RTR bit checking code for the MCP_CAN::mcp2515_read_canMsg() method implementation is done as following:

spi_readwrite(buffer_load_addr);
// mcp2515 has auto-increment of address-pointer
for (i = 0; i < 4; i++) tbufdata[i] = spi_read();

*rtrBit=(tbufdata[3]&0x08 ? 1 : 0 );

According to the datasheet of MCP2515 (please also refer to #62 for the details), the RTR bit is the 5th bit (bit 4) in the RXBnSIDL register. However, since buffer_load_addr is either MCP_READ_RX0 or MCP_READ_RX1. which points to RXBnSIDH register, tbufdata[3], the 4th byte of 4-byte consecutive read, is RXBnEID0 rather than RXBnSIDL, and the bit mask 0x08 is also incorrect either. This makes this RTR bit checking code returns completely incorrect result.

If #62 has been fixed, the proper implementation would be something as the following:

*rtrBit=(tbufdata[MCP_SIDL]&MCP_RTR_MASK ? 1 : 0 );

[Pillar1989]

If you feel you need to continue the discussion, you can reopen the issues.