On Thu, May 21, 2015 at 9:46 AM, Stefan Roese <s...@denx.de> wrote: > Hi Stefano, > > On 21.05.2015 18:17, Stefano Babic wrote: >> >> On 19/05/2015 15:26, Tim Harvey wrote: >> >>> Note that Falcon mode also requires you have a function in the SPL >>> that decides to boot U-Boot or to skip it and boot the OS directly. In >>> the Gateworks Ventana case I didn't want to make this completely >>> dependent on a GPIO/Button because this bootloader supports about 8 >>> different PCB designs in the Ventana family - some of which do not >>> have buttons or may not have buttons loaded on the board. Instead, I >>> pulled env support into the SPL and use 'boot_os' env var to decide as >>> other boards do (see spl_start_uboot()). >> >> >> Anyway, this can be dangerous. The reason having a GPIO (or any trigger >> from external, for example a received char from the console) is to >> switch to U-Boot if the kernel does not work (but the kernel image is >> not corrupted), mainly go to panic, and the board can be restored into >> U-Boot. >> >> If you use an environment variable and the environment is put into the >> NAND (with MMC you can change the card), there is nothing you can do >> anymore. Board tries to boot until next panic, and then again and again. > > > Some boards just don't have such a means as a push button or jumper to > select the Falcon mode. That's why I introduced this environment variable > dependent way to select Falcon mode quite some time ago for a PPC based > board. > > You are correct. If something goes completely wrong, and the board tries to > boot into the OS with a non-working OS installed, then you are doomed. JTAG > comes in handy then as I have experienced myself. ;) > > But this is usually only while developing this feature and kernel. Once its > tested and mature, this really works. > > Again, its a trade-off since another, better method to switch between > U-Boot- and OS- booting is not available. > > Thanks, > Stefan >
Agreed - this is exactly why I decided (at cost) to use an env variable - not all of our boards have a gpio that makes sense and I am am focusing on flexibility. Tim _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot
