I’m writing a MCP2518fd driver (for an ESP32) and am using my Logic Analyzer to measure timing. I have a simple „echo“ program where the MCP repeats every CAN frame it receives. The sender is a pretty fast Linux machine using cangen can0 -I 777 -L 8 -D r -v -v -g 1000 I’m also monitoring this (on the same machine) via candump -D -catd can0 Here’s an excerpt from a few seconds: (000.000000) can0 777 [8] 94 F8 BF 7E F1 6E 68 6B '...~.nhk' (000.000770) can0 777 [8] 94 F8 BF 7E F1 6E 68 6B '...~.nhk' (000.999518) can0 777 [8] 0E 99 51 48 E6 FF CE 64 '..QH...d' (000.000733) can0 777 [8] 0E 99 51 48 E6 FF CE 64 '..QH...d' (000.999406) can0 777 [8] AC 1C A4 01 B7 10 FC 7C '.......|' (000.000854) can0 777 [8] AC 1C A4 01 B7 10 FC 7C '.......|' (000.999348) can0 777 [8] 53 DA B4 5B 58 EA B4 5C 'S..[X..\' (000.000769) can0 777 [8] 53 DA B4 5B 58 EA B4 5C 'S..[X..\' (000.999483) can0 777 [8] BF 2E 36 77 49 52 A0 1D '..6wIR..' (000.000796) can0 777 [8] BF 2E 36 77 49 52 A0 1D '..6wIR..' (000.999389) can0 777 [8] 16 EF B7 22 85 F0 83 12 '..."....' (000.000735) can0 777 [8] 16 EF B7 22 85 F0 83 12 '..."....' (000.999357) can0 777 [8] BA C4 BF 45 E3 7C CD 73 '...E.|.s' (000.000845) can0 777 [8] BA C4 BF 45 E3 7C CD 73 '...E.|.s' (000.999404) can0 777 [8] 95 1B 65 1C 81 15 DB 64 '..e....d' (000.000731) can0 777 [8] 95 1B 65 1C 81 15 DB 64 '..e....d‘ Now I really wonder about these values, in particular the time between the „question“ and the „answer“. This is a CAN 2.0B bus @ 500000bps with only two nodes. Looking at my Logic Analyzer, it takes me about 160µs to send the received frame back into the MCP, where then the arbitration starts on the CAN bus. It takes an additional 200µs for the frame to be sent on the bus, so I’d expect to see a maximum of 360µs, if this is using hardware timestamps. I could only see 750µs, if I were to measure from the beginning of the „question“ and the end of the „answer“ frame, but that’s make sense. Is my understanding of these timestamps wrong? Cheers, :M:
