linux-kernel - Re: [PATCH v5 4/4] iplink_can: add new CAN FD bittiming parameters: Transmitter Delay Compensation (TDC)

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Message-ID: <20210816081205.7rjdskaui35f3jml@pengutronix.de>
Date:   Mon, 16 Aug 2021 10:12:05 +0200
From:   Marc Kleine-Budde <mkl@...gutronix.de>
To:     Vincent Mailhol <mailhol.vincent@...adoo.fr>
Cc:     Stephen Hemminger <stephen@...workplumber.org>,
        linux-can@...r.kernel.org,
        Stefan Mätje <stefan.maetje@....eu>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 4/4] iplink_can: add new CAN FD bittiming parameters:
 Transmitter Delay Compensation (TDC)

On 14.08.2021 19:17:28, Vincent Mailhol wrote:
> At high bit rates, the propagation delay from the TX pin to the RX pin
> of the transceiver causes measurement errors: the sample point on the
> RX pin might occur on the previous bit.
> 
> This issue is addressed in ISO 11898-1 section 11.3.3 "Transmitter
> delay compensation" (TDC).
> 
> This patch brings command line support to nine TDC parameters which
> were recently added to the kernel's CAN netlink interface in order to
> implement TDC:
>   - IFLA_CAN_TDC_TDCV_MIN: Transmitter Delay Compensation Value
>     minimum value
>   - IFLA_CAN_TDC_TDCV_MAX: Transmitter Delay Compensation Value
>     maximum value
>   - IFLA_CAN_TDC_TDCO_MIN: Transmitter Delay Compensation Offset
>     minimum value
>   - IFLA_CAN_TDC_TDCO_MAX: Transmitter Delay Compensation Offset
>     maximum value
>   - IFLA_CAN_TDC_TDCF_MIN: Transmitter Delay Compensation Filter
>     window minimum value
>   - IFLA_CAN_TDC_TDCF_MAX: Transmitter Delay Compensation Filter
>     window maximum value
>   - IFLA_CAN_TDC_TDCV: Transmitter Delay Compensation Value
>   - IFLA_CAN_TDC_TDCO: Transmitter Delay Compensation Offset
>   - IFLA_CAN_TDC_TDCF: Transmitter Delay Compensation Filter window
> 
> All those new parameters are nested together into the attribute
> IFLA_CAN_TDC.
> 
> A tdc-mode parameter allow to specify how to operate. Valid options
> are:
> 
>   * auto: the transmitter automatically measures TDCV. As such, TDCV
>     values can not be manually provided. In this mode, the user must
>     specify TDCO and may also specify TDCF if supported.
> 
>   * manual: Use the TDCV value provided by the user are used. In this
                           ^^^^^                      ^^^
                           singular                   plural
>     mode, the user must specify both TDCV and TDCO and may also
>     specify TDCF if supported.
> 

Marc

-- 
Pengutronix e.K.                 | Marc Kleine-Budde           |
Embedded Linux                   | https://www.pengutronix.de  |
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