On Monday 06 February 2012 19:20:21 jonsm...@gmail.com wrote: > On Mon, Feb 6, 2012 at 1:08 PM, Florian Fainelli <flor...@openwrt.org> wrote: > > On Monday 06 February 2012 18:00:17 Peter Naulls wrote: > >> On 02/06/2012 08:52 AM, jonsm...@gmail.com wrote: > >> > Most ARM CPUs have boot ROMs for getting the initial image out of > >> > flash. I'm referring to the boot loader that loads uboot, not uboot. > >> > The ARM CPUs I've worked with search for a signature in flash, if they > >> > can't find a valid signature they load from UART instead. Or you can > >> > use a jumper to force loading from UART. This allows you to recover > >> > from being bricked or initially load the flash without needing a > >> > special programmer. > >> > > >> > Do the MIPS based router CPUs have this ability? What does the on MIPS > >> > CPU ROM do if the image in flash is invalid? > >> > >> MIPS systems varies as much as ARM ones do. The short answer, is > >> it depends upon the hardware. For systems which lack serial/ROM > >> level recovery, you'll need to use JTAG. Some systems I work > >> with lack even that. > > > > Actually, I have never seen a single MIPS system out there having such a > > boot ROM capability. > > It is a very useful ability. You can solder the flash chips on empty > and then use the UART to program them during test. > > UART first loads a little program to tiny on-CPU-chip SRAM. This > program in turns knows how to program the flash chip and then reads > the full image from UART with error detection. You need the SRAM > because the DRAM controller is not set up yet. u-boot support this, > check out CONFIG_SPL. > > Takes about 30 seconds and no special equipment to initially program > our ARM boards. Same procedure can unbrick them.
Yeah, I have used that on a custom AT91 board, it definitively is useful, but MIPS integrators did not feel the need to get this standardized or even brought to customers, so, if you want a similar feature, you'd have to use a custom bootloader and protect the region of the flash where this rescue bootloader is. -- Florian _______________________________________________ openwrt-devel mailing list openwrt-devel@lists.openwrt.org https://lists.openwrt.org/mailman/listinfo/openwrt-devel
