Hi Marc,
> -----Original Message-----
> From: Marc Kleine-Budde <mkl@xxxxxxxxxxxxxx>
> Sent: Friday, March 18, 2022 4:21 AM
> To: Srinivas Neeli <sneeli@xxxxxxxxxx>
> Cc: Srinivas Goud <sgoud@xxxxxxxxxx>; Naveen Kumar Gaddipati
> <naveenku@xxxxxxxxxx>; Prasad Beer Prasad <prasadbe@xxxxxxxxxx>; linux-
> can <linux-can@xxxxxxxxxxxxxxx>; Stefan Mätje <stefan.maetje@xxxxxx>;
> Vincent MAILHOL <mailhol.vincent@xxxxxxxxxx>
> Subject: Re: Queries on CAN frame work
>
> On 21.02.2022 14:43:57, Srinivas Neeli wrote:
> > > Can you also provide the hand calculated bit timing parameters for
> > > the above scenarios?
> >
> > Baud rate 1/5Mbps
> > ================
> >
> > Hand configuration:
> > ---------------------------
> > ip link set can0 type can tq 12 prop-seg 29 phase-seg1 30 phase-seg2
> > 20 sjw 1 dtq 12 dprop-seg 5 dphase-seg1 6 dphase-seg2 4 dsjw 1 fd on
> > (A/D: 1/5Mbps, Sample point=75%)
> >
> > Baud rate 1/4Mbps
> > ================
> >
> > Hand configuration:
> > --------------------------
> > ip link set can0 type can tq 12 prop-seg 29 phase-seg1 30 phase-seg2
> > 20 sjw 1 dtq 12 dprop-seg 7 dphase-seg1 7 dphase-seg2 5 dsjw 1 fd on
> > (A/D: 1/4Mbps, Sample point=75%)
>
> 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")
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.
> | 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.
>
> regards,
> Marc
>
> --
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