CAN Send and Receive with Hardware Timestamping

Transcription

1 CAN Send and Receive with Hardware Timestamping esd electronic system design gmbh 1

2 Outline Motivation Timestamps Timestamped TX Use Cases Summary 2 Oxfordian Kissuth - Eigenes Werk, CC BY-SA 3.0,

3 Motivation Hardware based timestamps in CAN controllers Best properties of timestamps Use cases in higher level protocols 3

4 Timestamp Capturing Software E.g. Interrupt service routine High resolution counter of the host CPU Depending on the reaction time of the host system Hardware FPGA/ASIC based High accuracy 4

5 Timestamp Frequency Shortest distance of CAN Frames 47 µs Minimum timestamp frequency of 21.3 khz Map every CAN event in correct order Minimum timestamp frequency of 1 MHz Time quantum is the smallest unit in CAN Minimum timestamp frequency: CAN controller frequency 5

6 Timestamp Width 16 bit timestamp wraps every 0.82 ms 32 bit timestamp wraps every 53.7 s 64 bit timestamp wraps every 7312 years Recalculation in absolute time 64 bit timestamps require more logic and memory 6

7 Timestamp Sources External source e.g. IRIG-B CAN-Bus Node 1 Node 2 Node n IRIG-B IRIG-B Generator 7

8 Timestamp Properties Timestamp frequency equal CAN controller frequency 64 bit timestamp width Possibility of external timestamp sources Optional capture at Start of Frame 8

9 Timestamped TX TX-FIFO with sending time Approximate real-time behaviour on nonreal-time operating systems Accuracy of one bit time 9

10 Arbiter CAN Controller CAN-Bus Timestamped TX Structure of the Timestamped TX concept User Application CAN Driver CAN Hardware cansend TX Queue CAN Core in FPGA TX FIFO cansendt TX-TS Queue CM Sn CM S3 CM S2 CM S1 CM Tx... CM TF... CM t3 CM tm CM t2 CM t1 TX-TS FIFO t m t 3 t 2 t 1 TX-TS Window CM tm CM t3 CM t2 CM t1 1. Stage 2. Stage 3. Stage 10

11 Timestamped TX: Example Frames from TX-TS FIFO will be send as soon as possible to the next bit time Frames will be aborted after a configured timeout Fully compliant with ISO CM S1 t D CM t1 t 11 t 1 t A CM S2 CM S3 t A t 2 t 3 t A CM t2 CM t3 t A CM CM tm CM S4 Sn... aborted t m

12 Use Cases Highly accurate CAN logging Replay exact CAN log again Residual bus simulation Precise sync generation Higher level protocols (e.g. ARINC 825) Timestamp synchronisation via CAN 12

13 Summary High precision hardware based timestamps improve the accuracy in areas where CAN is used Hardware timestamps result in higher accuracy compared to software timestamps Hardware based timestamps in CAN controller frequency guarantee high precision timestamp resolution 13

14 Summary Absolute time in hardware offers a variety of advantages, like: TX-FIFO with a 64 Bit timestamp which contains the sending time Approximate real-time behaviour in non-realtime operating systems Hardware support for higher level protocols 14