osmo-gsm-tester: support gpio controlled step attenuators of the LTHW main unit
Patch  implements initial support for RF channel emulator for ENB objects. We should add support for the step attenuator connected to the sysmocom's osmo-gsm-tester setup.
- File pinouts.jpg pinouts.jpg added
- Status changed from Feedback to New
- Assignee changed from dexter to pespin
The step attenuator is controlled via the GPIO interface of the APU directly. As far as I know there are 4 attenuators. The synchronous serial interface is wired in parallel while the latch enable lines are wired individually. The attenuation value is shifted into the internal shift-register of all attenuator at once. The latch enable line latches the value to the outputs of the shift register to the register that controls the attenuation.
There is a git repository with a driver and a utility
The attenuator is an ZX76-31R5-SP+ from Mini-Circuits.
As far as I remember the GPIO chip in the APU is an NCT5104, some Info about the driver can be found here: https://github.com/tasanakorn/linux-gpio-nct5104d/pull/3/files