3 ms·

> U-Boot, or rather Das U-Boot a.k.a the Universal Boot Loader, is a small program that is loaded into read-only memory (ROM) This is wrong. You cannot load a

by fmntf 6y ago

> U-Boot, or rather Das U-Boot a.k.a the Universal Boot Loader, is a small program that is loaded into read-only memory (ROM) This is wrong. You cannot load a binary into a ROM memory. On most SoCs, thr bootloader is loaded in some RAM (DDR, OCRAM, TCM, or similar).

dmitrygr 6y ago
> You cannot load a binary into a ROM Nonsense. The terms to google for are "boot ROM" or "XIP". Boot Roms execute from rom because all that is available at the time. XIP binaries run from NOR or ROM happily
- fmntf 6y ago
  UBoot is not generally stored in boot ROM. The boot ROM loads the UBoot binary from somewhere (eg. eMMC, SD, etc) to some RAM, and jumps there. In case of in place execution, that is not ROM anyway. You may XIP from a NOR memory, but that is still not ROM.
  - rjsw 6y ago
    There are several ARM dev boards on the desk next to me that have U-Boot in ROM.
- htebhtbwyer 6y ago
  you're talking about different things. u-boot is not a boot rom. the actual bootrom is a maskrom on the a64. the maskrom looks to spi/mmc for spl and u-boot. notably neither spl nor u-boot are xip in this case. spi/mmc are both easily overwritten from within u-boot (or any os loaded later) u-boot is not a boot rom. it is a bootloader.
embuxaway 6y ago
Eh, I dunno. I've been working with embedded Linux recently and this seems like a pretty good write-up. "ROM" might be a bit of a misnomer for re-writable non-volatile memory, but it makes sense in the context. "Loaded into ROM" means that an external device like a laptop burns the code into non-volatile memory, it doesn't describe what the SoC does every time that it boots. This article even explains how the A64 loads its initial boot logic into RAM, although there are a couple of extra steps thanks to the "ARM Trusted Firmware" security elements: >Bootstrapping is complicated by initial memory address space limitations. The SPL is limited to 32 KiB, most likely because the BootROM, or BROM, loads the SPL into SRAM A1, which is a 32 KiB subsection. If the SPL is larger than 32 KiB the BROM will refuse to load it. After the SPL loads U-Boot proper and passes execution to the ATF, U-Boot proper in turn runs the Pine Phone’s u-boot command script. So...I don't think I understand your complaint. It seems to me that the article does explain how "thr bootloader is loaded in some RAM".

by fmntf 6y ago

dmitrygr 6y ago

> You cannot load a binary into a ROM Nonsense. The terms to google for are "boot ROM" or "XIP". Boot Roms execute from rom because all that is available at the time. XIP binaries run from NOR or ROM happily

fmntf 6y ago
UBoot is not generally stored in boot ROM. The boot ROM loads the UBoot binary from somewhere (eg. eMMC, SD, etc) to some RAM, and jumps there. In case of in place execution, that is not ROM anyway. You may XIP from a NOR memory, but that is still not ROM.
- rjsw 6y ago
  There are several ARM dev boards on the desk next to me that have U-Boot in ROM.
htebhtbwyer 6y ago
you're talking about different things. u-boot is not a boot rom. the actual bootrom is a maskrom on the a64. the maskrom looks to spi/mmc for spl and u-boot. notably neither spl nor u-boot are xip in this case. spi/mmc are both easily overwritten from within u-boot (or any os loaded later) u-boot is not a boot rom. it is a bootloader.

embuxaway 6y ago

Eh, I dunno. I've been working with embedded Linux recently and this seems like a pretty good write-up. "ROM" might be a bit of a misnomer for re-writable non-volatile memory, but it makes sense in the context. "Loaded into ROM" means that an external device like a laptop burns the code into non-volatile memory, it doesn't describe what the SoC does every time that it boots. This article even explains how the A64 loads its initial boot logic into RAM, although there are a couple of extra steps thanks to the "ARM Trusted Firmware" security elements: >Bootstrapping is complicated by initial memory address space limitations. The SPL is limited to 32 KiB, most likely because the BootROM, or BROM, loads the SPL into SRAM A1, which is a 32 KiB subsection. If the SPL is larger than 32 KiB the BROM will refuse to load it. After the SPL loads U-Boot proper and passes execution to the ATF, U-Boot proper in turn runs the Pine Phone’s u-boot command script. So...I don't think I understand your complaint. It seems to me that the article does explain how "thr bootloader is loaded in some RAM".