This article is written on an open-source operating system, but not an open-source machine — the BIOS isn’t open-source, and even if it were supported by the coreboot project (formerly LinuxBIOS), there would still be a whole host of binary blobs required to get it to boot. On one vintage architecture, there’s one less blob, as coreboot can now initialize DRAM on Intel Bay Trail SOCs, as [Mate Kukri] presented in a talk at the recent Open Source Firmware Conference.
Bay Trail isn’t exactly cutting-edge hardware, to be sure — the SoCs are over a decade old at this point, and were only used in low-performance mobile applications like Chromebooks. On the other hand, coreboot has been on Chromebooks for at least as long. Getting DRAM set up is difficult because, well, you don’t have any memory to work with until you do. Traditionally, the way you did that was to call on one of the many proprietary ‘binary blobs’ provided with next to no documentation by the manufacturer. Reverse engineering that requires some serious bus-sluthing, which was done in software with the SerialICE debugger and the Unicorn Engine CPU emulator. The talk focused on that technique and how it might be applied more widely, rather than getting into the weeds of how to do DRAM init on one obsolete SOC. At some point the whole thing should be archived on the OFSC website so those of us not lucky enough to attend in person can hear what [Mate] — and all the other speakers — had to say.
Continue reading “Coreboot Hikes The Bay Trail To DRAM Initialization”
