this Xenomai RTDM driver is intended to synchronize Xenomai RT threads to an external clock via interrupts on a GPIO pin. it enables an RT thread to wait for an edge (rising or falling) on an arbitrary pin. Tested on beaglebone. Should not be much different for other ARM platforms. Doubles as a GPIO RTDM driver to read/write/toggle GPIO pins from an RT thread, see the GPIO_IRQ_PIN_* ioctls and the usage example in gpio-irq-test.c . Assumes config-pin has been used already for proper pinmuxing, see load.sh for an example. To exercise the demo: --------------------- - connect P8.9 to some timing source (I used the 1kHz reference clock of my scope with a 100 ohm resistor in series) - scope pins P8.9, P8.10 and P8.11 - run sudo ./load.sh P8.10 will change as the RTDM driver IRQ routine starts, roughly 5uS post the trigger. P8.11 will change as the userspace RT thread becomes unblocked, roughly 10-15uS post trigger. see http://static.mah.priv.at/public/rtdm-chain.png P8.9 = green = clock P8.10 = red = RTDM irq handler started P8.11 = yellow = userspace RT thread becomes unblocked To change the pins, note currently "kernel GPIO numbers" are used. To map a certain P8/P9 pin to a kernel GPIO number, see https://github.com/cdsteinkuehler/beaglebone-black-pinmux/blob/hal_pru_generic/pinmux.ods for a given P8/P9 pin, take the values from the 'GPIO bank' and 'GPIO pin' columns (N and O). The pin number is GPIO_Bank_Number * 32 + GPIO_Pin_number. Alternatively, look at the config-pin script, for example P8.9: P8_09_PRU="101" P8_09_GPIO="69" <---- kernel GPIO number P8_09_PIN="gpio" P8_09_PINMUX="default gpio gpio_pu gpio_pd timer" P8_09_INFO="gpio2_5 default gpio2_5 gpio2_5 gpio2_5 timer5" P8_09_CAPE="cape-universal cape-universaln" inspecting while load.sh is running: ------------------------------------ mah@epig:~/gpio-irq-rtdm$ cat /proc/xenomai/stat CPU PID MSW CSW PF STAT %CPU NAME 0 0 0 6913006 0 00500080 99.3 ROOT 0 14341 0 21460 0 00300182 0.0 trivial <--- userland RT thread 0 0 0 902569 0 00000000 0.0 IRQ67: [timer] 0 0 0 21459 0 00000000 0.0 IRQ197: gpio69 <--- RTDM IRQ thread mah@epig:~/gpio-irq-rtdm$ cat /proc/xenomai/irq IRQ CPU0 67: 765486 [timer] 197: 3550220 gpio69 <---- RTDM IRQ handler 1027: 2615635 [virtual] The second field (count) should increase continuously. Driver information: mah@epig:~/gpio-irq-rtdm$ cat /proc/xenomai/rtdm/gpio_irq/information driver: gpio_irq_rtdm version: 0.0.0 peripheral: GPIO_IRQ RTDM provider: machinekit class: 224 sub-class: 4711 flags: NAMED_DEVICE lock count: 1 Module parameters, doubling as statistics counters: mah@epig:~/gpio-irq-rtdm$ cat /sys/module/gpio_irq_rtdm/parameters/ completions interrupts timing_pin mah@epig:~/gpio-irq-rtdm$ cat /sys/module/gpio_irq_rtdm/parameters/completions 58032 mah@epig:~/gpio-irq-rtdm$ cat /sys/module/gpio_irq_rtdm/parameters/interrupts 64073 Some inspirations were taken from code by Pierre Ficheux: see https://github.com/pficheux/raspberry_pi/tree/master/Xenomai/RT_irq Michael Haberler 6/2015