u-blox : layers are confusing me

[Hans Mayer]

Dear All,

my environment:

U-blox ZED-F9P with version 27.12

gpsd: 3.25.1~dev (revision release-3.25-48-gfa2081388)

Debian GNU/Linux 11 (bullseye)

I am trying to understand the layers, especially with the baudrate configuration.

This is the situation after a RESET

UBX-CFG-VALGET:
 version 1 layer 0 position 0
  layers (ram)
    item CFG-UART1-BAUDRATE/0x40520001 val 38400

UBX-ACK-ACK:
  ACK to Class x06 (CFG) ID x8b (VALGET)

UBX-ACK-NAK:
  NAK to Class x06 (CFG) ID x8b (VALGET)

UBX-ACK-NAK:
  NAK to Class x06 (CFG) ID x8b (VALGET)

UBX-CFG-VALGET:
 version 1 layer 7 position 0
  layers (default)
    item CFG-UART1-BAUDRATE/0x40520001 val 38400

UBX-ACK-ACK:
  ACK to Class x06 (CFG) ID x8b (VALGET)

Now I am running

ubxtool -z CFG-UART1-BAUDRATE,115200,0 localhost:gpsd:/dev/serial0

and I am wondering why gpsd can still access the device with 38400 bd

When I look for the settings I get the same result as above. I try it with layer 1

ubxtool -z CFG-UART1-BAUDRATE,115200,1 localhost:gpsd:/dev/serial0

Now communications is broken to the ZED-F9P. I have to reconfigure the gpsd with 115200 bd

I have the following situation, layer 0 has 115200 bd 

UBX-CFG-VALGET:
 version 1 layer 0 position 0
  layers (ram)
    item CFG-UART1-BAUDRATE/0x40520001 val 115200

UBX-ACK-ACK:
  ACK to Class x06 (CFG) ID x8b (VALGET)

UBX-ACK-NAK:
  NAK to Class x06 (CFG) ID x8b (VALGET)

UBX-ACK-NAK:
  NAK to Class x06 (CFG) ID x8b (VALGET)

UBX-CFG-VALGET:
 version 1 layer 7 position 0
  layers (default)
    item CFG-UART1-BAUDRATE/0x40520001 val 38400

UBX-ACK-ACK:
  ACK to Class x06 (CFG) ID x8b (VALGET)

Now I do the same with 2

ubxtool -z CFG-UART1-BAUDRATE,115200,2 localhost:gpsd:/dev/serial0

and layer 1 (bbr) is changed

UBX-CFG-VALGET:
 version 1 layer 0 position 0
  layers (ram)
    item CFG-UART1-BAUDRATE/0x40520001 val 115200

UBX-ACK-ACK:
  ACK to Class x06 (CFG) ID x8b (VALGET)

UBX-CFG-VALGET:
 version 1 layer 1 position 0
  layers (bbr)
    item CFG-UART1-BAUDRATE/0x40520001 val 115200

UBX-ACK-ACK:
  ACK to Class x06 (CFG) ID x8b (VALGET)

UBX-ACK-NAK:
  NAK to Class x06 (CFG) ID x8b (VALGET)

UBX-CFG-VALGET:
 version 1 layer 7 position 0
  layers (default)
    item CFG-UART1-BAUDRATE/0x40520001 val 38400

UBX-ACK-ACK:
  ACK to Class x06 (CFG) ID x8b (VALGET)

What happens with 3 ?

ubxtool -z CFG-UART1-BAUDRATE,115200,3 localhost:gpsd:/dev/serial0

nothing, same config as before

and with 4

ubxtool -z CFG-UART1-BAUDRATE,115200,4 localhost:gpsd:/dev/serial0

now layer 2 changed

UBX-CFG-VALGET:
 version 1 layer 0 position 0
  layers (ram)
    item CFG-UART1-BAUDRATE/0x40520001 val 115200

UBX-ACK-ACK:
  ACK to Class x06 (CFG) ID x8b (VALGET)

UBX-CFG-VALGET:
 version 1 layer 1 position 0
  layers (bbr)
    item CFG-UART1-BAUDRATE/0x40520001 val 115200

UBX-ACK-ACK:
  ACK to Class x06 (CFG) ID x8b (VALGET)

UBX-CFG-VALGET:
 version 1 layer 2 position 0
  layers (flash)
    item CFG-UART1-BAUDRATE/0x40520001 val 115200

UBX-ACK-ACK:
  ACK to Class x06 (CFG) ID x8b (VALGET)

UBX-CFG-VALGET:
 version 1 layer 7 position 0
  layers (default)
    item CFG-UART1-BAUDRATE/0x40520001 val 38400

UBX-ACK-ACK:
  ACK to Class x06 (CFG) ID x8b (VALGET)

I am quite sure there is an explanation. The ZED-F9P interface description PDF is in general very useful but didn't give me a solution for my question.

It seems there is sometimes an offset of 1 but not always

Kind regards

Hans

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