> On 01/30/2012 09:07 PM, Bud Miljkovic wrote: > > Hi there, > > > > > > > > While getting acquainted with possible u-Boot development issues, I read > > FAQ "14.2.1. Can U-Boot be configured such that it can be started in > > RAM?" and was puzzled to learn that u-Boot cannot run from RAM. > > > > > > > > Considering a custom platform, using i.MX536, I understand that the > > i.MX53x processor has its own ROM-based code that performs boot time > > essential devices initialisation, etc. In the case when NAND flash is > > the program-image medium at the boot stage, first, the ROM-based code > > checks for Discovered Bad Blocks Table (DBBT) presence and searches for > > valid Firmware Configuration Block (FCB) on external NAND Flash. > > > > > > > > If FCB is found that points to the NAND Flash page(s) that contain the > > first 4K of initial firmware to be loaded from NAND Flash. Then, it > > loads the 4K of data, pointed by FCB, into the NFC RAM buffer. These > > data contain a valid Image Vector Table (IVT). Then, the ROM-based code > > processes IVT, executes the Device Configuration Data (DCD) sequences to > > initialize boot-related integrated peripherals (typically, these are > > IOMUX, SDRAM controller and boot memory controller), then copies the > > application code, also contained in IVT, to target memory (typically, > > SDRAM) and jumps to it. Typically, this application code is the custom > > primary bootloader that completes loading the application code (e.g. > > main OS bootloader) and passes the control to it. > > > > > > > > If FCB is not found the ROM-based code starts executing a download > > protocol over UART or USB port in an attempt to get a valid IVT from a > > host. If the IVT is eventually obtained it is processed as before. > > > > > > > > So the question is can this "custom primary bootloader" role, in fact, > > be played by u-Boot. Reading your text of FAQ 14.2.1., it seems to me > > that it cannot. On the other hand I know of some Freescale i.MX53x demo > > boards (e.g. ARD, LOCO) that use u-Boot. > > > > > > > > I wonder what I'm missing here. > > I think that FAQ is a bit misleading and really refers to using another > boot loader to load U-Boot.
The FAQ really means "is it possible to load u-boot from u-boot" ... which is possible in some cases, but officially unsupported. > > On all i.MX processors I've had the pleasure of using, U-Boot runs only > from RAM. I think you probably knew this because very few i.MX designs > even have other memory (i.e. NOR flash) that allows XIP. > > For instance, the LOCO certainly isn't running __from__ SD card. > > Take a look at the link maps for builds of these platforms to clarify. Yep, MX53 is well supported by mainline u-boot. M > > _______________________________________________ > 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
