Hello Satz, A bit of history - until a few years ago, the u-boot project only produced a single binary output (u-boot.bin or u-boot.img) that you loaded for your board. The resulting binary usually comes to about 200 - 250kB (approx). Then Texas Instruments began manufacturing the OMAP line of SOC's that had some static-RAM built into the chip. The idea was that we could have some initialization code to setup the bare environment before doing other things. A limitation was that the SRAM had a capacity of just a few kB (think less than 50kB, I don't remember what the exact number is).
So, (I presume) someone from TI make a fork of the u-boot code base to produce a "minimal" boot-loader called X-loader. The resulting binary came to about 25kB or so. The boot sequence thus went like this; ROM code (we can't edit this) -> X-loader (in SRAM) -> u-boot (in DDR RAM) -> Linux system. (for details see here: http://omappedia.org/wiki/Bootloader_Project) Normal DDR ram doesn't "just work". You need something to initialize the clocks (and possibly power?), before the processor can make use of it. This is was X-loader did. Eventually, other manufacturers (Samsung? nVidia? not sure if Freescale uses it....) picked up on the idea of having SRAM in their SOC's for initialization purposes and instead of maintaining two separate code-bases, an idea cropped up to merge X-loader back into the u-boot source. This was eventually done and that's where we are today. Now, to "edit the bootloader", Satz, you'll want to understand the build process. The MLO file does not "magically" appear. It is actually built on your computer right after u-boot gets built. In a nutshell, when you run, > make omap3_beaglebone_config (I forgot what the actual config is) A few configuration files get created. This is in preparation for the next step, which is; > make The above is an instruction to the uboot build system to scan the configuration files and build whatever system was specified. In the case of beagleboneblack (and omap processors) this happens in 2 different stages. First, the entire source tree is scanned/compiled to create the "u-boot.bin" (or u-boot.img) file. Then the build system re-starts the scan to compile the MLO file. If you browse the source, you'll see code like "#if SPL_CONFIG" (or similar). These are the sections that instruct the build system to create the MLO file. Hope it answers your question? :) Drinking coffee, Abraham On Thu, Dec 5, 2013 at 2:04 AM, Satz Klauer <satzkla...@googlemail.com> wrote: > Hi Tom, > > point is, I want to change some functionality of bootloader - thus I > want to know where it is built from. It is nice when MLO file appears > automagically but in my special case I like to know where it comes > from exaclty. > > Thanks :-) > > > On Wed, Dec 4, 2013 at 3:58 PM, Tom Rini <tr...@ti.com> wrote: >> On Wed, Dec 04, 2013 at 03:08:43PM +0100, Satz Klauer wrote: >> >>> Hi, >>> >>> I'm looking for the sources of the MLO bootloader that is used on >>> BeagleBone Black by default. A posting within TIs webboard pointed me >>> to this location but ... where are the sources? While checking the GIT >>> repositiory I could not find anything that looked like "MLO" or >>> "BeagleBone Black". >> >> When you build for am335x_evm you get both u-boot.img and MLO files that >> work on a number of boards from TI that use the am335x chip, including >> Beaglebone Black. >> >> -- >> Tom > _______________________________________________ > U-Boot mailing list > U-Boot@lists.denx.de > http://lists.denx.de/mailman/listinfo/u-boot _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot
