Enabling option ROM and flashing gPXE on an SMC 1211

If you're going to play with PCI option ROMs, you're likely to salvage a PCI Network Interface Card (NIC) with a flash ROM, or at least one that has a socket for it. And given their popularity in the late 90s/early 2ks, you have a fair chance getting your hands on with a RealTek RT8139 based one. One such NIC is is the SMC 1211 (or "Accton Technology Corporation SMC2-1211TX" as reported by lscpi -nn on Linux), which, in its basic configuration, comes with a DIP socket for 5V flash chips up to 128 KB in size. This is actually quite a desirable card to have as it is beautifully supported by flashrom, which has great support for the RT8139 chip, and no extra tweaking is needed to support the maximum flash size of 128 KB, as can be the case with other NICs. Add a W29C011A-15 or compatible, which can be easily obtained or salvaged from an old motherboard and you'll have more than enough space to play with an option ROM.

Only problem of course is that most SMC 1211s don't come with a flash chip by default so the option ROM is disabled and needs to be re-enabled. Luckily, Realtek does provide a tool called rset8139.exe to do just that. Of course, rather than blindly trusting the tool before we go and play with a custom option ROM, we may as well attempt to check that everything is in order so we are first going to flash a proper one, such as gPXE before running the rset8139 tool. Off we go then to etherboot/gPXE's awesome rom-o-matic, fill our options, including the 1113:1211 VID:PID of our SMC card and get our gPXE ROM back then.

First order of the day, since we're using a 128 KB flash chip and the gPXE ROM we got was smaller, is pad our ROM to our target size with:

cat gpxe-1.0.1-11131211.rom /dev/zero | dd bs=1k count=128 > gpxe_128k.rom

Then we flash with:

flashrom -p nicrealtek -w gpxe_128k.rom

So that takes care of having a proper option ROM. Of course, since we haven't enabled it on the card, you will find that no matter the options you select in your BIOS, the SMC option ROM is not executed and this is precisely why we need to run that rset8139 utility. Now, it is possible that Linux or Windows version of this utility exist, but it looks like the most common version is the DOS one, which, thanks to the oh-so-convenient Rufus (see this post), running from a DOS bootable USB stick is no problem at all.

One important thing to note is there exists multiple versions of the utility, ranging from 5.00 to 5.09, and that not all of these appear to detect the SMC 1211 card. Some regression has been introduced by Realtek, which leaves the most recent versions of rset8139 unable to change settings for the 1211. Therefore, the version I recommend using if you have an SMC card is v5.01, which can be picked here. If you don't have an SMC card, then you can try your luck with v5.0.9, which appears to be the most recent, and which is available here.

Once you have created your DOS bootable USB stick and copied rset8193.exe over, you should end up with something similar to the screenshot below (courtesy of desconexão.net), where you will be able to enable and set your ROM size:

After these settings are saved and you reboot, you should find that the gPXE option ROM payload is now executed by your BIOS, and with that you can get cracking on building a custom option ROM using your RT8139 based card.