On 18.03.2022 06:55:56, Srinivas Neeli wrote:
> > I've updated the algorithm to prefer lower brp values. Can you check
> > if these values make sense to you?
>
> Thanks for update.
> Few more changes need to update in algorithm.
> 1) Choose SJW as large as possible (we can assign " tseg2")
ACK - changes to SJW needs still to be done.
> For CANFD CIA recommendations :
> Recommendation 1:
> Choose the highest available CAN clock frequency (20 MHz, 40 MHz, 80 MHz)
> Recommendation 2:
> Set the BRPA bit-rate pre-scaler equal BRPD
> Recommendation 3:
> Choose BRPA and BRPD as low as possible.
> Recommendation 4:
> Configure all CAN FD nodes to have the same arbitration phase Sample point (SP) and the same data phase SP
> Recommendation 5:
> Choose SJWD and SJWA as large as possible (best is the max possible value)
> Recommendation 6:
> Enable TDC when needed
> If we enable TDC feature ,please try to configure brp value 1 in algorithm(TDC feature support brp 1/2 but observed good results with 1).
> >
> > | $ ./can-calc-bit-timing --alg=can-next xilinx_dwnstrm -c 79999999 Bit
> > | timing parameters for xilinx_dwnstrm with 79.999999 MHz ref clock (cmd-
> > line) using algo 'can-next'
> > | nominal real Bitrt nom real SampP
> > | Bitrate TQ[ns] PrS PhS1 PhS2 SJW BRP Bitrate Error SampP SampP Error
> > | 1000000 12 29 30 20 1 1 999999 0.0% 75.0% 75.0% 0.0%
>
> Observed different BRP values for 1Mbps in here and below list for
> same sampling point.
Yes. Seems I should update the table to clarify what they output.
The 1st table uses the CAN-2.0 bit timing constants, the 2nd table is
using the CAN-FD data bit timing constants.
> > | 800000 12 39 40 20 1 1 799999 0.0% 80.0% 80.0% 0.0%
> > | 666666 12 47 48 24 1 1 666666 0.0% 80.0% 80.0% 0.0%
> > | 500000 12 69 70 20 1 1 499999 0.0% 87.5% 87.5% 0.0%
> > | 250000 25 69 70 20 1 2 249999 0.0% 87.5% 87.5% 0.0%
> > | 125000 50 69 70 20 1 4 124999 0.0% 87.5% 87.5% 0.0%
> > | 100000 50 87 87 25 1 4 99999 0.0% 87.5% 87.5% 0.0%
> > | 83333 50 104 105 30 1 4 83333 0.0% 87.5% 87.5% 0.0%
> > | 50000 100 87 87 25 1 8 49999 0.0% 87.5% 87.5% 0.0%
> > | 33333 125 104 105 30 1 10 33333 0.0% 87.5% 87.5% 0.0%
> > | 20000 250 87 87 25 1 20 19999 0.0% 87.5% 87.5% 0.0%
> > | 10000 500 87 87 25 1 40 9999 0.0% 87.5% 87.5% 0.0%
> > |
> > | Bit timing parameters for xilinx_dwnstrm with 79.999999 MHz ref clock
> > (cmd-line) using algo 'can-next'
> > | nominal real Bitrt nom real SampP
> > | Bitrate TQ[ns] PrS PhS1 PhS2 SJW BRP Bitrate Error SampP SampP Error
> > | 12000000 12 2 2 2 1 1 11428571 4.8% 75.0% 71.4% 4.8%
> > | 10000000 12 2 3 2 1 1 9999999 0.0% 75.0% 75.0% 0.0%
> > | 8000000 12 3 3 3 1 1 7999999 0.0% 75.0% 70.0% 6.7%
> > | 5000000 12 5 6 4 1 1 4999999 0.0% 75.0% 75.0% 0.0%
> > | 4000000 12 7 7 5 1 1 3999999 0.0% 75.0% 75.0% 0.0%
> > | 2000000 12 14 15 10 1 1 1999999 0.0% 75.0% 75.0% 0.0%
> > | 1000000 25 14 15 10 1 2 999999 0.0% 75.0% 75.0% 0.0%
>
> Here brp =2 and in above list brp =1.
According to the "ip" command's output, these are you timing parameters:
| .bittiming_const = {
| .name = "xilinx_dwnstrm",
| .tseg1_min = 1,
| .tseg1_max = 256,
| .tseg2_min = 1,
| .tseg2_max = 128,
| .sjw_max = 128,
| .brp_min = 1,
| .brp_max = 256,
| .brp_inc = 1,
| },
| .data_bittiming_const = {
| .name = "xilinx_dwnstrm",
| .tseg1_min = 1,
| .tseg1_max = 32,
| .tseg2_min = 1,
| .tseg2_max = 16,
| .sjw_max = 16,
| .brp_min = 1,
| .brp_max = 256,
| .brp_inc = 1,
| },
Note that for the data bit timing the tseg1_max is 32.
> > | nominal real Bitrt nom real SampP
> > | Bitrate TQ[ns] PrS PhS1 PhS2 SJW BRP Bitrate Error SampP SampP Error
> > | 1000000 12 29 30 20 1 1 999999 0.0% 75.0% 75.0% 0.0% <-- CAN-2.0
> > | 1000000 25 14 15 10 1 2 999999 0.0% 75.0% 75.0% 0.0% <-- CAN-FD (data)
\_____/
tseg1
tseg1 = 14 + 15 = 29
With brp == 1 the tseg1 would be 29 + 30 = 59, which means it's too
large.
regards,
Marc
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