jsln/pps-gen-gpio

Linux kernel PPS generator using GPIO pins

pps-gen-gpio's Issues

Doesn't work if system time is changed

If system time is changed forwards, the PPS generator stars sending We are late this time... continuously. This can be fixed by replacing ts_expire_req by ts_expire_real in this line.

Question: When does PPS signal get generated

Is the PPS signal generated when system time starts a new second, or is it generated at some arbitrary time?

Testing gpio output with linuxptp

Hi Juan,

This is more a question than an issue. Ive downloaded your code into kernel 4.4 and Ive compiled it and put it on the beaglebone black. Ive modprobed your driver and i see it coming up, which is good.
[ 134.924519] random: nonblocking pool is initialized
[ 204.818461] pps_gen_gpio: GPIO PPS signal generator
[ 204.824485] pps_gen_gpio: found 1 GPIOS defined in DT
[ 204.829789] pps_gen_gpio pps-generator: GPIO lookup for consumer pps-gen
[ 204.829802] pps_gen_gpio pps-generator: using device tree for GPIO lookup
[ 204.829834] of_get_named_gpiod_flags: parsed 'pps-gen-gpios' property of node '/pps-generator[0]' - status (0)
[ 204.829950] no flags found for pps-gen
[ 204.830096] pps_gen_gpio: port write takes 2381ns
[ 256.003929] pps_gen_gpio: we are late this time 255.999972447
[ 779.003925] pps_gen_gpio: we are late this time 778.999970551
[ 792.003931] pps_gen_gpio: we are late this time 791.999972719
[ 1614.003930] pps_gen_gpio: we are late this time 1613.999972984

Now, ive connected an oscilloscope between GND and pin 16 (im using the same dts config as you) but im not seeing anything on the output.

I would like to have this signal synced to linuxptp as well.

Am i missing something? Should I be seeing anything on the output on this case?

Thanks

David

This driver not working with kernel 4.4

Hi Jsolano,

I am trying to use your driver with the Linux Kernel version 4.4, but it gives the following error:

drivers/pps/generators/pps_gen_gpio.c: In function ‘pps_gen_gpio_probe’:
drivers/pps/generators/pps_gen_gpio.c:201:22: error: too few arguments to function ‘devm_gpiod_get’
devdata->pps_gpio = devm_gpiod_get(dev, "pps-gen");
^
In file included from include/asm-generic/gpio.h:13:0,
from ./arch/arm/include/asm/gpio.h:9,
from include/linux/gpio.h:48,
from drivers/pps/generators/pps_gen_gpio.c:32:
include/linux/gpio/consumer.h:73:32: note: declared here
struct gpio_desc *__must_check devm_gpiod_get(struct device *dev,

I am expecting that the new kernel calls devm_gpiod_get differently. Is it possible that that is the case?

Thanks in advance.

pps impulse jitter

Hi) I've tested that module and I want to use it... But I would like to improve accuracy. The impulse jitter is about 2 - 7 us. The main reason I think is the jitter of gpiod_set_value() function... Also sometimes the pulse is not generated because of delay for entering interrupt... Can you give me some clue about how to get rid of these drawbacks? Maybe it is reasonable to use some Timer in pwm mode instead of gpio... I'm using AM335x SoC (Beagle Bone Black board).

How do I use this from scratch?

I have previously setup NTP/PTP/etc on a Beagle bone black before; but I am struggling incorporating this at the moment.
Could you provide some more verbose steps for configuring a PPS from a blank BBB? Thank you kindly.