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NV Read not working after updating single NV item

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Thanks Meter: 2
By lahcim2000, Junior Member on 27th March 2019, 04:56 AM
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I had two Samsung S10+ phones: SM-G975U1 (US Unlocked version) and SM-G9750 (China HK version).
Both are running the same Qualcomm Snapdragon chipset.

I wanted to enable additional bands on SM-G9750 to make it fully in sync with SM-G975U1.

What I did was the following:
1) Installed QXDM tool
2) Read the following NVs: 00441, 00442, 00946, 01877, 02954, 06828.
3) Noticed that the only difference is on the 1877 (CDMA config) and 6828 (LTE config)
4) Updated the 1877 and 6828 to be exactly the same as the values from SM-G975U1.
5) Rebooted phone

Everything was working. After rebooting the phone I connected again and was able to read the values I wrote and they were showing correct (written values).
Then I decided to be "smarter". I noticed that even though my SM-G9750 has now values from SM-G975U1, when I compare the bits from what was on SM-G9750 before and what is now (config I took from SM-G975U1) there is still one bit that was set for SM-G9750 and now was reset by the new configuration from SM-G975U1.
So I decided to make "OR" and set this bit.

After saving the values, everything went well. I was able to save it and read it back.
Then I rebooted the phone.

Phone works after reboot, connects and everything but now there was an interesting issue...
When I connected it to the QXDM I cannot read *ANY* NV values. Even for other slots. I am getting invalid command all the time.
DFS Qualcomm tool that used to work also does not work.

Looks like the USB is listening but not accepting any commands.

What could have happened? And how do I revert it back?
Phone in general is working, just cannot read or modify any NV values via USB, as if the software working there on phone that was serving USB requests got disabled, crashed, or blocked.



For reference, those are the original values from both phones:




USA: 1877: CDMA:
0010 0000 0000 0000 0000 0000 0110 1110 1000 0100 0011 1000 0111

CHINA: 1877: CDMA:
0010 0000 0000 0000 0000 0000 0110 1110 1000 0000 0011 1000 0011

USA/CHINA: 2954:
4294967295 (or 0xFFFFFFFF)

USA: 6828: LTE:

0000 0100 0000 0010 0000 0001 1110 0000 0011 1011 0000 1110 0011 1000 1101 1111

CHINA: 6828: LTE:

0000 0000 0000 0010 0010 0001 1110 0000 0011 1000 0000 1110 0010 1000 1101 1111
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