Re: [PATCH v5 2/7] can: bittiming: allow TDC{V,O} to be zero and add can_tdc_const::tdc{v,o,f}_min

On 16.08.2021 16:30:52, Marc Kleine-Budde wrote:

quoted

Finally, I did a bit of research and found that:
http://ww1.microchip.com/downloads/en/DeviceDoc/Section_56_Controller_Area_Network_with_Flexible_Data_rate_DS60001549A.pdf

quoted

This is *not* the mcp25xxfd datasheet but it is still from
Microship and as you will see, it is mostly similar to the
mcp25xxfd except for, you guessed it, the TDCO.

It reads:
| TDCMOD<1:0>: Transmitter Delay Compensation Mode bits
| Secondary Sample Point (SSP).
| 10 = Auto; measure delay and add CFDxDBTCFG.TSEG1; add TDCO
| 11 = Auto; measure delay and add CFDxDBTCFG.TSEG1; add TDCO
| 01 = Manual; Do not measure, use TDCV plus TDCO from the register
| 00 = Disable

| TDCO<6:0>: Transmitter Delay Compensation Offset bits
| Secondary Sample Point (SSP). Two's complement; offset can be
positive, zero, or negative.
| 1111111 = -64 x SYSCLK
| .
| .
| .
| 0111111 = 63 x SYSCLK
| .
| .
| .
| 0000000 = 0 x SYSCLK

Here, you can clearly see that the TDCO has the exact same range
as the one of the mcp25xxfd but the description of TDCMOD
changes, telling us that:

| SSP = TDCV (measured delay) + CFDxDBTCFG.TSEG1 (sample point) + TDCO

Which means this is a relative TDCO.

Good catch! Microchip is investigating this.

regards,
Marc

-- 
Pengutronix e.K.                 | Marc Kleine-Budde           |
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