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 14:25:19, Marc Kleine-Budde wrote:

quoted

quoted

I'm not sure, if we talked about the mcp251xfd's tcdo, valid values are
-64...63.

Yes! Stefan shed some light on this. The mcp251xfd uses a tdco
value which is relative to the sample point.

I don't read the documentation this way....

quoted

| SSP = TDCV + absolute TDCO
|     = TDCV + SP + relative TDCO

Consequently:
| relative TDCO = absolute TDCO - SP

In the mcp15xxfd family manual
(http://ww1.microchip.com/downloads/en/DeviceDoc/MCP251XXFD-CAN-FD-Controller-Module-Family-Reference-Manual-20005678B.pdf)
in the 2mbit/s data bit rate example in table 3-5 (page 21) it says:

| DTSEG1  15 DTQ
| DTSEG2   4 DTQ
| TDCO    15 DTQ

The mcp251xfd driver uses 15, the framework calculates 16 (== Sync Seg+
tseg1, which is correct), and relative tdco would be 0:

| mcp251xfd_set_bittiming: tdco=15, priv->tdc.tdc=16, relative_tdco=0

Here the output with the patched ip tool:

Sorry, the previous output was not using the sample points of the
example in the data sheet, this is the fixed output:

| 6: mcp251xfd0: <NOARP,UP,LOWER_UP,ECHO> mtu 72 qdisc pfifo_fast state UP mode DEFAULT group default qlen 10
|     link/can  promiscuity 0 minmtu 0 maxmtu 0 
|     can <FD,TDC_AUTO> state ERROR-ACTIVE (berr-counter tx 0 rx 0) restart-ms 100 
|           bitrate 500000 sample-point 0.800
|           tq 25 prop-seg 31 phase-seg1 32 phase-seg2 16 sjw 1 brp 1
|           mcp251xfd: tseg1 2..256 tseg2 1..128 sjw 1..128 brp 1..256 brp_inc 1
|           dbitrate 2000000 dsample-point 0.800
|           dtq 25 dprop-seg 7 dphase-seg1 8 dphase-seg2 4 dsjw 1 dbrp 1
|           tdco 16
|           mcp251xfd: dtseg1 1..32 dtseg2 1..16 dsjw 1..16 dbrp 1..256 dbrp_inc 1
|           tdco 0..127
|           clock 40000000 numtxqueues 1 numrxqueues 1 gso_max_size 65536 gso_max_segs 65535 parentbus spi parentdev spi0.0 

Marc

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