Jetson Nano 2GB dev kit GPIO toggle speed from Python?

I’m working on interfacing an HX711 with a Jetson Nano 2GB dev kit (the eventual application will interface with a Xavier NX, but just proof-of-concepting things here). This is my first time working with the Nano and for a start, I’m just trying to do the same thing I did on a Raspberry Pi (and an old RPi at that - I think it’s a model 2?).

I’m using a Python library ( GitHub - gandalf15/HX711: Read HX711 ADC for Weigh Scales on Rasperry PIs. ) which interfaces using the RPi.GPIO interface - which I was pleased to see is emulated by the Jetson GPIO interface. I was able to successfully toggle some of the pins on the Nano (including the pins which I’m using) with Python.

When I use the HX711 library, however, it’s unable to communicate with the HX711 device, because it’s not able to toggle the GPIO fast enough (an operation which works fine on the Pi). In specific, the clock pin can’t stay high for more than 60us (ie, 0.00006s) or else the HX711 shuts down - and according to the debug timing in the lib I’m using, it takes on the order of 2ms(!) to toggle the clock pin on this Jetson Nano 2GB dev kit.

Is this expected? If I rewrite the pin toggling in C and use the sysfs interface for GPIO, can I expect better performance, or do I have to write a kernel driver for this?


hello riz-nvidia,

may I know what’s your expectation,
you need to program the GPIO via kernel level to have better performance,

My expectation was that it would yield similar performance to a six-year-old Raspberry Pi. (Where, as I said, this does toggle in under 60us)

What you seem to be saying, though, is a userspace driver (even written in C) is not going to work on the Nano?

hello riz-nvidia,

please refer to GPIO Bit-Bang Speed Increase - #23 by Bibek,
please have a try to increase clock rate to get better results.

I looked there, but the suggestion

root@tegra-ubuntu:/sys/kernel/debug/bpmp/debug/clk/axi_cbb# cat rate

…doesn’t work on this Nano because there’s no “bpmp” node in /sys/kernel/debug:

riz@jetson-nano:~$ sudo ls /sys/kernel/debug/
57000000.gpu	      iio	  pwm			 tegra_gpio
57000000.gpu_scaling  isp	  ras			 tegra_hdmi
70006040.serial       isp.1	  regmap		 tegra_host
70006200.serial       ixgbe	  regulator		 tegra_la_ptsa
7000d400.spi	      mc	  sdhci-tegra.0		 tegra_latency
7000d600.spi	      memblock	  sleep_time		 tegra_mipi_cal
70019000.iommu	      mlxsw_core  soctherm		 tegra_pinctrl_reg
asoc		      mmc0	  split_huge_pages	 tegra_sor1
bdi		      msenc	  suspend_stats		 tegra_throttle
bluetooth	      nvdec	  sync			 tegra_vi
clk		      nvjpg	  system_states		 tegra_xhci
cpuidle_t210	      nvlink	  tegra-pmc-io-pads	 tegradc.0
debug_enabled	      nvmap	  tegra-rtc		 tracing
dma_buf		      opp	  tegra_bwmgr		 tsec
dri		      pcie	  tegra_camera_platform  tsecb
dynamic_debug	      pg_domains  tegra_central_actmon	 usb
extfrag		      pinctrl	  tegra_denver		 vi
fault_around_bytes    pm_genpd	  tegra_dfll_fcpu	 vic
gpio		      pm_qos	  tegra_dvfs		 virtio-ports
gpu.0		      pmc-reset   tegra_ec		 wakeup_sources
hid		      powergate   tegra_emc

I’d be happy to try bumping some clock rate as long as I know which one.

hello riz-nvidia,

oh, that axi_cbb is only available for TX2 series.

please refer to this example,
you may have a try for using mmap to have faster speed.