How do you build er9x from source?

[Petroid]

Hello!
I'm trying to build er9x from source for my DIY 9x clone based on atmega128 with telemetry.
I was not able to find any documentation on building from source apart from README on https://github.com/MikeBland/mbtx which is terribly outdated. Currently I've got a problem. I'm building er9x with options:
make CPU=128 EXT=FRSKY
Supposedly this way the firmware will expect THR_CUT and AIL_DR switches to be on 41 and 42 pins of MCU with telemetry enabled on pins 2 and 3. But that does not happen. The THR_CUT and AIL_DR are still expected on pins 2 and 3.
Could I be missing some steps or build options?
Any building manual or at least explanation on build options would be greatly appreciated too.

EDIT: Apparently the telemetry isn't working too.

[MikeB]

The '128 version has an option in the hardware menu to indicate you have the "FrSky Mod Done", it doesn't need a special build.
To enable the hardware menu, hold the left horizontal trim to the left as you power on.

Mike.

[Petroid]

Thank you so much!
I was also wondering where is hardware menu That solved the problem.