So here's the deal. RS232 vs RS485 mode control is not exposed in a documentable way. However, it IS exposed through an EFI variable that can be written to — but in a giant blob of configuration shared by a bunch of other BIOS configuration variables. You can't edit the settings in isolation, but you CAN save different values of the entire configuration variable, and one of them will have the port in 232 mode, while another could have it in 485 mode. Any of this could be discovered by a customer by tweaking BIOS settings and looking at what changed in the EFI variable store, so that's why I'm pretty comfortable disclosing all of this.
Let me describe the downsides to this approach a little more clearly than "your hair will fall out". Obviously, this is very unsupported, but there's a little more to it than that. If this configuration variable (which includes the port setting) gets screwed up, your controller is probably hosed. This can happen if, for instance, you lose power while updating the configuration. But it could also happen if you restore a different controller's configuration by accident. Or if you restore a config from the SAME controller, but a DIFFERENT firmware version. If you're lucky, you might be able to recovery reset the firmware configuration settings. More likely, you're looking at an RMA. All that said: if this works for you, on your controller, under a controlled execution environment, it is likely to continue working.
With that out of the way: see attached for a script I cobbled together to automate most of this. I would describe the testing of this utility as "loose". I wish to repeat that this utility is completely unsupported. You must understand shell script programming in order to effectively deploy this utility. Usage is going to go something like this:
- At system development time:
- Install niefinvctl to /usr/local/bin with mode 755.
- Get the firmware config the way you want it.
- Run `niefinvctl -b cfg1` to save the current config to a file.
- Make sure niefinvctl and the config file storage location (currently /var/local/niefinvctl) are included in your system image.
- At deployed system boot time (you'll need to get this logic into your image too):
- An init script, of your devising, runs on startup, which in turn runs `niefinvctl -5 -r cfg1`. If the file setting differs from the firmware setting, the firmware is updated; otherwise, no change is made. If the exit code is 5, reboot to make sure the settings take effect.
(EDIT: Utility updated to require opt-in for restore to work, and to abort if config was saved with a different BIOS version or model.)
