Re: [PATCH 2/2] can: add Transmitter Delay Compensation (TDC) documentation
From: Simon Horman <horms@kernel.org>
Date: 2025-10-13 09:42:04
Also in:
linux-can, linux-doc, lkml
On Sun, Oct 12, 2025 at 08:23:43PM +0900, Vincent Mailhol wrote: ...
quoted hunk ↗ jump to hunk
@@ -1464,6 +1464,66 @@ Example when 'fd-non-iso on' is added on this switchable CAN FD adapter:: can <FD,FD-NON-ISO> state ERROR-ACTIVE (berr-counter tx 0 rx 0) restart-ms 0 +Transmitter Delay Compensation +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +At high bit rates, the propagation delay from the TX pin to the RX pin of +the transceiver might become greater than the actual bit time causing +measurement errors: the RX pin would still be measuring the previous bit. + +The Transmitter Delay Compensation (thereafter, TDC) resolves this problem +by introducing a Secondary Sample Point (SSP) equal to the distance, in +minimum time quantum, from the start of the bit time on the TX pin to the +actual measurement on the RX pin. The SSP is calculated as the sum of two +configurable values: the TDC Value (TDCV) and the TDC offset (TDCO). + +TDC, if supported by the device, can be configured together with CAN-FD +using the ip tool's "tdc-mode" argument as follow:: + +- **omitted**: when no "tdc-mode" option is provided, the kernel will
Hi Vincent, I'm unsure why, but make htmldocs reports: .../can.rst:1484: ERROR: Unexpected indentation. [docutils]
+ automatically decide whether TDC should be turned on, in which case it + will calculate a default TDCO and use the TDCV as measured by the + device. This is the recommended method to use TDC.
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