On 24.02.2021 09:20:04, 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 adds two new structures: can_tdc and can_tdc_const in order > to implement this TDC. > > The structures are then added to can_priv. > > A controller supports TDC if an only if can_priv::tdc_const is not > NULL. > > TDC is active if and only if: > - fd flag is on > - can_priv::tdc.tdco is not zero. > It is the driver responsibility to check those two conditions are met. > > No new controller modes are introduced (i.e. no CAN_CTRL_MODE_TDC) in > order not to be redundant with above logic. > > The names of the parameters are chosen to match existing CAN > controllers specification. References: > - Bosch C_CAN FD8: > https://www.bosch-semiconductors.com/media/ip_modules/pdf_2/c_can_fd8/users_manual_c_can_fd8_r210_1.pdf > - Microchip CAN FD Controller Module: > http://ww1.microchip.com/downloads/en/DeviceDoc/MCP251XXFD-CAN-FD-Controller-Module-Family-Reference-Manual-20005678B.pdf > - SAM E701/S70/V70/V71 Family: > https://www.mouser.com/datasheet/2/268/60001527A-1284321.pdf > > Signed-off-by: Vincent Mailhol <mailhol.vincent@xxxxxxxxxx> > --- > include/linux/can/bittiming.h | 65 +++++++++++++++++++++++++++++++++++ > include/linux/can/dev.h | 3 ++ > 2 files changed, 68 insertions(+) > > diff --git a/include/linux/can/bittiming.h b/include/linux/can/bittiming.h > index 707575c668f4..91bf9f8926a7 100644 > --- a/include/linux/can/bittiming.h > +++ b/include/linux/can/bittiming.h > @@ -1,5 +1,6 @@ > /* SPDX-License-Identifier: GPL-2.0-only */ > /* Copyright (c) 2020 Pengutronix, Marc Kleine-Budde <kernel@xxxxxxxxxxxxxx> > + * Copyright (c) 2021 Vincent Mailhol <mailhol.vincent@xxxxxxxxxx> > */ > > #ifndef _CAN_BITTIMING_H > @@ -10,6 +11,70 @@ > > #define CAN_SYNC_SEG 1 > > +/* > + * struct can_tdc - CAN FD Transmission Delay Compensation parameters > + * > + * 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. > + * > + * To solve this issue, ISO 11898-1 introduces in section 11.3.3 > + * "Transmitter delay compensation" a SSP (Secondary Sample Point) > + * equal to the distance, in time quanta, from the start of the bit > + * time on the TX pin to the actual measurement on the RX pin. > + * > + * This structure contains the parameters to calculate that SSP. > + * > + * @tdcv: Transmitter Delay Compensation Value. Distance, in time > + * quanta, from when the bit is sent on the TX pin to when it is > + * received on the RX pin of the transmitter. Possible options: > + * > + * O: automatic mode. The controller dynamically measure @tdcv ^ I think this is supposed to be a 0, not a O? I'll send a patch > + * for each transmited CAN FD frame. regards, Marc -- Pengutronix e.K. | Marc Kleine-Budde | Embedded Linux | https://www.pengutronix.de | Vertretung West/Dortmund | Phone: +49-231-2826-924 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |
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