@mariog@hirose I understand this request comes from your side. Could you describe the use case?
It shouldn't be a huge issue to implement, but I'm sceptical you have the right use case for this. Typically we should always have a specific order to power up the different power domains. You can not really infer any concurrency from switching two channels at the same time (as their impedance might change differently over time)
Maybe that's a very particular use case, but this would be useful for us when building IV or VI curves from Rd53a. What we're currently doing is fixing one channel (e.g. vddd) and ramping e.g. the Voltage from the other one. So for this we need to power the ASIC from two different channels. Also, for each step, we power it off and on in order to reset it. That currently means four steps: vdda off, vddd off, vdda on, vddd on.
If we could just switch off the main output, we would reduce this to two steps (main output off and on), saving a bit more than half a second per step. That would also make the code a bit simpler. I believe someone would eventually face a more decisive use case when using LR for a purpose different than ours. In our case, this would just improve a bit something that already works fine.
What we have done in this particular case is just activate/deactivate the main output when channel "0" is "selected" (doing "INST:NSEL 0" + "OUTPUT:GENERAL ON"), and independently activate/deactivate the specified channel otherwise ("INST:NSEL 1" + "OUTPUT:SELECT ON"). That was just the easiest to implement, but I believe adding this functionality to LR in a proper way would mean a much more significant change in the repository.