Has anyone tried the following FTDI USB to USB Null Modem Cable for serial debugging?
The Serial Debugging page describes a usual serial null modem cable or USB to serial adapter, but I don’t have a computer with a serial port, and certainly don’t plan to buy one. The USB-to-USB NMC looks to be the right solution. If anyone has one, please let me know where you ordered it.
Just looks like a male to male USB cable…
Something like this, perhaps - USB 3.0 A Male to Male Plug Cable Lead High Speed 50cm 1m 2m 3m 5m | eBay UK
No, it only looks like that, but there are FTDI chips in the null modem cable to emulate serial port connection. A regular male to male USB is a great way to fry out the motherboard if two hosts are connected, it’s not compliant with the USB spec, nevertheless some manufacturers uses it to connect their devices. I have one exactly like the one you posted, it came with some Chinese SSD enclosure.
I think you can just get two FTDI cables with 9 pin connectors and connect the ends together with a NULL modem adapter (2->3, 3->2, 5->5, 4->6, 6->4, 7->8, 8->7, if memory serves).
However I do not think this is the thing you want. That page suggests using a USB serial adapter only to access the serial output from a machine under test, that itself has a built in serial port. It’s pretty clear that the system being tested (that you want debug output from) needs a built in serial port, not a USB one. It’s possible that has changed, but I haven’t heard about it and in that case the page info is out of date too.
No, that’s still correct. Serial debugging only works if the debugged machine has a serial port accessible as an IO device directly (with the IN and OUT instructions). This cannot be done with USB.
So your options are built-in to the mother board, PCI cards, ExpressCard, and maybe anything else that does PCI-Express if you can find a suitable serial adapter (in theory it’s possible on M2 sockets and possibly on thunderbolt, but as far as I know no one makes suitable hardware for that).
My idea was to use it for an early phase UEFI debugging like Jessica mentioned here:
There’s (a bit of experimental) FTDI driver in EDK II, after the call to ExitBootServices() I assume it should collapse, but Jessica mentions:
This will also extend to kernel debugging, which will be able to continue to use the USB serial port for debugging using traditional port i/o.
I think it’s worth trying, since I need it also for stuff unrelated to Haiku.
Thanks for reminding about Thunderbolt. It should work, yes. Thunderbolt → M.2 enclosure → PCI Express with COM port. The hardware is available, but for my older MacBook with Thunderbolt 2 I would also need to get an enclosure with dedicated power connector, as TB2<>TB3 adapter doesn’t deliver power in the direction to the TB3 device. I used to have the necessary enclosure, so I know which model should work. But to be honest, I don’t really want to build that Frankenstein on my table unless absolutely necessary.