ROS doesn't have drivers for regular USB controllers, so it will see the pci-e device but will not be able to use it. I have used "mining" adapter from mini-PCIe to regular PCIe slot and tried various PCI-E cards I had on hand (usb controllers, wlans, serial port adapters, network cards, soundcard,...) and pretty much nothing worked. No kernel drivers for anything in ROS. In system/resources/PCI I could always see pci IDs of the card, but that was it. Only card that somewhat worked was 4 port serial that appeared as usable ports.
This is just limitation of ROS, in openwrt it's possible to either find package with required drivers or compile the module yourself... but ROS is closed and there's nothing we can do, which is a shame. Also thanks to Mikrotik still shipping devices with 16MBs of flash, there's little chance of having build with more kernel drivers included - as they are counting every kilobyte to fit into that small flash now... (but hey... it's totally not a limitation and everything is fine and 16MBs is enough for everybody...)
r00t, I really despise hijacking threads, especially a years old one, but the PM functionality of this board is not enabled, leaving me little choice. Please excuse me for doing so.
I am looking to purchase/test some 2 and 4 port RS232 miniPCIe cards and see that you have had at least some success with this in the past, though I cannot tell from this thread what RB model or serial card model you were successful with, nor is there any such cards listed on the MT compatible peripherals page. My dilemma is that the Manufacturer of the ones I am eyeballing (IOCrest) is not responding to requests as to whether their card uses the USB2 pins or the PCIe pins. The RBM33G slots support either, but other RBs like the KNOT LR8/9 only support USB mode (or so the block diagrams would have me believe). In the end, I am hoping to add 4x RS232 ports to the KNOT LR9 by replacing the LoRa miniPCIe card, as it only comes with RS485 but otherwise has everything I want (no need for the LoRa, but you don't get the extra slot unless you spend the extra $100 over the base KNOT model).
Any insight into specific models and successes/failures you had would help me to not spend time and money on paperweights.