On 5/5/19 7:18 AM, Joakim Zhang wrote:
> Flexcan driver shows:
>
> static const struct can_bittiming_const flexcan_bittiming_const = {
> .name = DRV_NAME,
> .tseg1_min = 4,
> .tseg1_max = 16,
> .tseg2_min = 2,
> .tseg2_max = 8,
> .sjw_max = 4,
> .brp_min = 1,
> .brp_max = 256,
> .brp_inc = 1,
> };
>
> Could you explain briefly why the minimum of TSEG1(Prop_Seg +
> Phase_Seg1) in flexcan driver is 4 ?
>
> From IMX6DQ RM:
It's set to 4 due to the same or similar picture in the datasheets of:
- mx25
- mx28
- mx35
- mx53
- mx6 (Document Number: IMX6DQRM, Rev. 5, 06/2018,
Document Number: IMX6SDLRM, Rev. 4, 07/2018)
- vf610
> I have checked with IC guys that the explanation and figure**in IMX6DQ
> RM is *incorrect*. It has been updated like this:
ok - is this datasheet available somewhere?
Is the fix also true for all above mentioned SoCs?
> •Time Segment 1: This segment includes the propagation segment and the
> phase segment 1 of the CAN standard. It
>
> can be programmed by setting CTRL1[PROPSEG] and CTRL1[PSEG1] so that
> their sum (plus 2) is in the range of 2 to
>
> 16 time quanta.
>
> Time Segment 2: This segment represents the phase segment 2 of the CAN
> standard. It can be programmed by setting
>
> CTRL1[PSEG2] (plus 1) to be 2 to 8 time quanta long.
>
> And the minimum value can be written into PROPSEG and PSEG1 field in
> CTRL1 register is 0.
>
> To my understanding, the minimum value of TSEG1 should be 2. Right?
Seems so. Feel free to send a patch mentioning the documentation flaw in
the datasheet.
> Another question is that CAN driver doesn’t ensure the total number of
> time quanta in a bit time programabled at least from 8 to 25 via CAN
> bittiming calculation(CAN_CALC_BITTIMING).
Where does this 8 to 25 limitation come from?
> This should check by user, right?
No, if there is a limitation, we should update the bit rate timing
calculation algorithm to take care of this.
Marc
--
Pengutronix e.K. | Marc Kleine-Budde |
Industrial Linux Solutions | Phone: +49-231-2826-924 |
Vertretung West/Dortmund | Fax: +49-5121-206917-5555 |
Amtsgericht Hildesheim, HRA 2686 | http://www.pengutronix.de |
Attachment:
signature.asc
Description: OpenPGP digital signature
