Documentation/stm32f4: document the Ethernet PTP support. - #20206
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The STM32F4 page did not say anything about the Ethernet MAC. - Describe the time counter of the MAC and the options that enable the timestamping of received packets, the pulse-per-second output and the use of the counter as a high-resolution RTC. - Describe the /dev/ptp0 clock that the driver registers: the operations it offers, the numbering, and that the timestamps of the received packets are values of the MAC counter and not of CLOCK_REALTIME, so they have to be compared with /dev/ptp0. - Show how to start ptpd with them and a configuration that enables everything above. - Say that the driver does not timestamp transmitted packets. Signed-off-by: Daniel P. Carvalho <danieloak@gmail.com> Assisted-by: Claude:claude-sonnet-5
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Summary
The STM32F4 platform page has no section about the Ethernet MAC, so nothing tells a user how to use the PTP support that the legacy STM32 Ethernet driver has, and the driver got a
/dev/ptp0PTP hardware clock in #20180. This PR adds an "Ethernet" section toDocumentation/platforms/arm/stm32f4/index.rst. It changes documentation only.The section describes, checked against
arch/arm/src/common/stm32/stm32_eth_m3m4_v1.c,Kconfig.ethand the pin maps:SYSCLK, rate adjustable by up to +/- 50 %) and why a PTP daemon needs it.CONFIG_STM32_ETH_PTP,CONFIG_STM32_ETH_ENHANCEDDESC,CONFIG_STM32_ETH_TIMESTAMP_RX,CONFIG_STM32_ETH_PTP_GPIO(with the two possible pins on the STM32F40xxx and STM32F42xxx parts and theGPIO_ETH_PPS_OUTthat the board defines in itsboard.h) andCONFIG_STM32_ETH_PTP_RTC_HIRES./dev/ptp0clock: the numbering (the number of the Ethernet interface), the operations it offers (time, resolution, frequency, phase) and the one it does not (cross timestamp), with a link to the PTP clock driver page.CLOCK_REALTIME, so a program has to compare them with/dev/ptp0. It shows how to startptpdthat way (ptpd -H -p /dev/ptp0 -i eth0) and a configuration that enables everything.Transmit timestamps are not described here because they are not in
masteryet; the section will get them when they are.Impact
Documentation only, no code change. Only the page
platforms/arm/stm32f4changes.Testing
Built the documentation with Sphinx 6.2.1 and the packages of
Documentation/Pipfile, without-W: the build succeeds, the new section renders and the link to the PTP clock driver page resolves. None of the 19 warnings (duplicate C declarations in other pages) is from this file../tools/checkpatch.shpasses.The statements were checked by reading the driver and the pin maps. The configuration example and the
ptpdcommand line were not built or run as written here; the driver andptpdwere run on an STM32F4 board with a similar configuration.