Retronetworking

h1. StarTech PEX16S952LP

The "StarTech PEX16S952LP":https://web.archive.org/web/20240219124205/https://cdn.cnetcontent.com/syndication/mediaserver/inlinecontent/stech/683/473/683473204caf40629ddc342ca128d7c5/original.pdf is a PCI-Express card with 16 RS-232 connectors using DB-9 cables. A CD is distributed, but it contains only some code for ancient Linux kernel. The card has support in the upstream kernel.

h2. Enabling UARTs

The "8250 Kconfig":https://elixir.bootlin.com/linux/v6.7.5/source/drivers/tty/serial/8250/Kconfig#L199 in the Linux kernel sets the default number of UARTs to 4, with the following note:

> Set this to the maximum number of serial ports you want the kernel to register at boot time.  This can be overridden with the module parameter "nr_uarts", or boot-time parameter 8250.nr_uarts

Unknown why the kernel has a hard coded default, but it's how it is.

create @/etc/default/grub/uarts.cfg@ with:

<pre>

GRUB_CMDLINE_LINUX_DEFAULT="${GRUB_CMDLINE_LINUX_DEFAULT} nr.uarts=16"

</pre>

Make sure to choose the right amount of UARTs for the *total* number in the entire computer. So you need to calculate the number of the 8520's in the PCIe card + any internal 8250's in the PC. In the case Eloy's Fujitsu E900, this is 17 because there is one internal UART.

Then run:

<pre>

su -

grub-update

</pre>

The @su -@ is important (at least in Debian), when using @sudo -s@ or something similar the @grub-update@ command does not work.

The numbers on the connectors are NOT the number in the Linux @/dev/ttySx@ device file. It is recommended to label them. It is unknown on basis Linux assigns the device file number, but it seems to be consistent with reboots.

To run @mgetty@ on all the serial interfaces, run the following command. It assumes that ttyS1 until ttyS15 is used, might be different for other hardware.

<pre>

for i in {1..15}; do sudo systemctl enable --now mgetty@ttyS"$i"; done

</pre>