Very Odd CAN Behaviour on LPC1549

[anmolthind]

Hi,

I'm currently working on a library for use on LPC15xx microcontrollers, part of the library is a CAN module and I'm seeing some really strange behaviour.

To better explain what I have, I have two stages to the library. The CAN module of the higher level library is built on a lower level CAN library I wrote to the Canpie spec, but the higher level library has a lot of other stuff like generic interfaces to GPIO, timers, UART etc.

Now when I test just the low level Canpie library functions, everything works fine. But when I use my higher level library the data segments in my CAN packets are not what they should be. The higher level library calls the exact same functions as my Canpie test does as well. Right now I'm trying to pass a CAN packet full of 0's in the data segment (DLC of 8) but my output has occasional bits changed or simply doesn't give out a valid CAN packet, though the ID is always fine. I really have no idea what could be causing this and would appreciate any help. I'm worried it could be some sort of memory or stack issue, but the DA registers on the C_CAN0 peripheral never go non-zero as far as I can see in debugging so I still have no idea what it could be.

I've attached a sample of the output I get from my Salae logic analyser, hooked up to the TX pin on the LPC1549 dev board, reminder that the data should be all zeroes. In case it helps anyone.

Time [s]	Analyzer Name	Decoded Protocol Result
2.255614	CAN	Extended CAN Identifier: 405898241
2.255686	CAN	Control Field: 8 bytes
2.255694	CAN	Data Field Byte: 0
2.255714	CAN	Data Field Byte: 0
2.255732	CAN	Data Field Byte: 0
2.255752	CAN	Data Field Byte: 0
2.255772	CAN	Data Field Byte: 8
2.255788	CAN	Data Field Byte: 0
2.255808	CAN	Data Field Byte: 0
2.255826	CAN	Data Field Byte: 0
2.255846	CAN	CRC value: 20654
2.255878	CAN	NAK
3.149655	CAN	Extended CAN Identifier: 405898241
3.149727	CAN	Control Field: 8 bytes
3.149735	CAN	Data Field Byte: 0
3.149755	CAN	Data Field Byte: 0
3.149773	CAN	Data Field Byte: 0
3.149793	CAN	Data Field Byte: 0
3.149813	CAN	Data Field Byte: 8
3.149829	CAN	Data Field Byte: 0
3.149849	CAN	Data Field Byte: 0
3.149867	CAN	Data Field Byte: 0
3.149887	CAN	CRC value: 20654
3.149919	CAN	NAK
4.220714	CAN	Extended CAN Identifier: 405898241
4.220786	CAN	Control Field: 8 bytes
4.220794	CAN	Data Field Byte: 0
4.220814	CAN	Data Field Byte: 0
4.220832	CAN	Data Field Byte: 0
4.220852	CAN	Data Field Byte: 0
4.220872	CAN	Data Field Byte: 8
4.220888	CAN	Data Field Byte: 0
4.220908	CAN	Data Field Byte: 0
4.220926	CAN	Data Field Byte: 0
4.220946	CAN	CRC value: 20654
4.220978	CAN	NAK
5.03876	CAN	Extended CAN Identifier: 405898241
5.038832	CAN	Control Field: 8 bytes
5.03884	CAN	Data Field Byte: 0
5.03886	CAN	Data Field Byte: 0
5.038878	CAN	Data Field Byte: 0
5.038898	CAN	Data Field Byte: 1
5.038916	CAN	Data Field Byte: 0
5.038934	CAN	Data Field Byte: 0
5.038954	CAN	Data Field Byte: 0
5.038972	CAN	Data Field Byte: 0
5.038992	CAN	CRC value: 20654
5.039024	CAN	NAK
5.869806	CAN	Extended CAN Identifier: 405898241
5.869878	CAN	Control Field: 8 bytes
5.869886	CAN	Data Field Byte: 0
5.869906	CAN	Data Field Byte: 0
5.869924	CAN	Data Field Byte: 0
5.869944	CAN	Data Field Byte: 0
5.869964	CAN	Data Field Byte: 8
5.86998	CAN	Data Field Byte: 0
5.87	CAN	Data Field Byte: 0
5.870018	CAN	Data Field Byte: 0
5.870038	CAN	CRC value: 20654
5.87007	CAN	NAK
6.634848	CAN	Extended CAN Identifier: 405898241
6.63492	CAN	Control Field: 8 bytes
6.634928	CAN	Data Field Byte: 0
6.634948	CAN	Data Field Byte: 0
6.634966	CAN	Data Field Byte: 0
6.634986	CAN	Data Field Byte: 0
6.635006	CAN	Data Field Byte: 8
6.635022	CAN	Data Field Byte: 0
6.635042	CAN	Data Field Byte: 0
6.63506	CAN	Data Field Byte: 0
6.63508	CAN	CRC value: 20654
6.635112	CAN	NAK