Critical Current Limit Jetson TX2: How to make the change persistent across boots

We have observed through an oscilloscope that, a surge current of 3.4 Amps occurs at approximately 3ms after power on. We are trying to control the surge current by changing the content of crit_current_limit_0 according to the solution given in Critical Current Limit Jetson TX2 - #5 by WayneWWW

However, the change is not persistent across boots. Are there any ways to make the change persistent across boots?

Also, in the same discussion thread, another solution proposed was: Critical Current Limit Jetson TX2 - #7 by WayneWWW

However, it’s not clear what the action item is supposed to be. Any clarity over the same would be greatly appreciated.
We would prefer a solution that would not involve reflashing the device.

Are you talking about you don’t know how device tree works here?

The post you shared already mentioned to modify things in device tree.

Please correct us if our understanding of device tree modification is wrong. We would also aprreciate any documentation or references with regard to this problem. This is what our understanding is:

  1. We need to modify the .dtsi files, build the device tree, replace dtb files and flash device tree.
  2. We understand that there is a method to do this without flashing the device. How to update dtb of TX2 without flashing - #3 by JerryChang
  3. We need to change the inrush current for both tx2 and tx2i without flashing.

We would greatly appreciate if you could outline the sequence of steps we need to follow.

Update from last time,

We were working towards finding the correct configuration for limiting the inrush current. The kernel source for 32.5.1 as well as the current build environment seem to have multiple dts files with the configurations. The dt property “current-critical-limit-ma” is not available for TX2I. Rather it seems to be only available for TX2 (Board ID 3310). However, we were able to figure out that “Board ID” for TX2I is 3489 and narrow down the specific dtb files and configuration requiring the change to limit the inrush current. The “System EDP” value is not clear yet, however we doubled the resistance value on “VDD_IN” rail to limit the inrush current from 3.6A to 1.8A.

We were able to achieve this by building the following 4 files after changing the resistance values.

  • tegra186-quill-p3489-0888-a00-00-base.dtb
  • tegra186-quill-p3489-1000-a00-00-ucm1.dtb
  • tegra186-quill-p3489-1000-a00-00-ucm1.dtb.rec
  • tegra186-quill-p3489-1000-a00-00-ucm2.dtb
  1. How do we calculate or obtain system EDP limit for Jetson TX2I?
  2. What is the default value of system EDP for Jetson TX2I?

Hi, as you can see in tabel Absolute Maximum Ratings in TX2 series module data sheet, the IDDmax is 3A, software limited. 3A is for VDDMAX(19V). Actual IDDMAX is dependent on VDD_IN (VDD_INMIN).

  1. We could not find the value of VDD_IN anywhere from tegrastats, jtop and other sources. However, we know that the input voltage to the device would be very close to 12V. Is this supposed to be considered as VDD_IN? Is the value of VDD_INMIN - 9.6 (As per the operating voltage limits from datasheet) or is it the input voltage at the time of operation?
  2. How would the VDD_IN help in calculating the system EDP limit?

We are working with TX2 and TX2i, we have observed that the profile plots of the inrush current with an oscilloscope in both the devices was different. We would like to know the cause of this.

Sorry for the late response, have you managed to get issue resolved or still need the support? Thanks

The issue is not resolved. Can you kindly check the previous comment?

As said, above means EDP is 19V x 3A = 57W. You can change the limit current according to the input voltage level.

The difference between TX2 and TX2i is normal since some devices on module are different.