Download APM:Copter V3.5.7 (B11c6af3) firmware for use with 3dr PX4

Hi

I’m new to the Pixhawk scene so please excuse me if I don’t get things quite right (Still reading to become more knowledgeable - Right now pretty confused)

Have 2 hardware identical 3dr PX4 FMUs which I are are running different autopilots versions (Believe Ardupilot). See at bottom for Unit #1 and #2 details (hopefully provide useful info)

Looking to make Unit #2 the same as unit #1 so I can test capturing serial data (GPS/MAvLink1) while on the ground (no live flight)

Questions:

  1. Can I downgrade the firmware on unit #2 to 3.5.7?
  2. If so, where can I download firmware 3.5.7 for my FMU (I’ve found release notes; but no firmware binaries)
  3. Can I use MissonPlanner and/or QGroundControl to export the settings from unit #1 into unit #2 to have similarly configured units?
  4. If I can export and import the settings, is there anything which could cause issues with doing this?
  5. Have been reading that there was some issues with the 3dr FMU with a limit of 1 meg of memory, and that there was a hardware revision + bootloader + firmware change to correct this. How would I tell if my hardware has the issue?
  6. Are there any console monitoring tools, where I could decode the MAvLink1 serial data (live and also play back captured data)

Any assistance, pointers, words of wisdom are greatly apricated

Sincerely

Paul

The hardware is https://ardupilot.org/copter/docs/common-pixhawk-overview.html

Unit #1
PX4: b535f974 NuttX: 1bcae90b
Frame: QUAD
PX4v2 00360034 30345111 37383933
APM:Copter V3.5.7 (b11c6af3)

Unit #2
PX4: 1e7ed30b NuttX: 1472b16c
Frame: QUAD
PX4v2 002B0035 3034510A 38323435
ArduCopter V3.6.12 (cb570c06)

Good day, personally i don’t advice downgrade the firmware also bcoz with the latest releases you can find bugs corrections.
As ive saw you still using firmware running ros NuttX. Now the ros in ardupilot is chios… that run more fast… low mcu and memory and the dimensions of the code permit to pack more features inside the code.
If your board support only 1mb flash you are limited in FMUv2