Add notes from working on bootstrap support Signed-off-by: Sam Ravnborg <sam@xxxxxxxxxxxx> --- .../boards/at91/microchip-at91sam9263-ek.rst | 122 +++++++++++++++++++++ 1 file changed, 122 insertions(+) diff --git a/Documentation/boards/at91/microchip-at91sam9263-ek.rst b/Documentation/boards/at91/microchip-at91sam9263-ek.rst index 74ddb3cdb..8022cdd67 100644 --- a/Documentation/boards/at91/microchip-at91sam9263-ek.rst +++ b/Documentation/boards/at91/microchip-at91sam9263-ek.rst @@ -8,3 +8,125 @@ Building barebox: .. code-block:: sh make ARCH=arm at91sam9263ek_defconfig + +Notes while working on at91sam9263ek bootstrap support + +The at91sam9263 have support for a boot program, +like the other members in the Atmel at91 series. + +The boot program (ROMBOOT) will try to load the +boot program from DataFlash, SD Card, NAND Flash and USB + +SD Card is the first to try. +It looks for a file named BOOT.BIN in the first +partition in a FAT16/32 filesystem. + +To generate the SD Card image I used genimage: +(https://github.com/pengutronix/genimage) +Onle 2 GB SD card works, 4 GB did not work. ROMBOOT do not +support high capacity SD cards. + +Configuration file: + +.. code-block:: none + + image boot.vfat { + name = "boot" + vfat { + /* + * RomBOOT in the at91sam9263 does not recognize + * the default FAT partition created by mkdosfs. + * -n BOOT - Set volume label to "BOOT" + * -F 16 - Force the partition to FAT 16 + * -D 0 - Set drive number to 0 + * -R 1 -a - Reserve only one sector + * The combination of "-D 0" AND "-R 1 -a" + * is required with mkdosfs version 4.1 + */ + extraargs = "-n BOOT -F 16 -D 0 -R 1 -a" + file BOOT.BIN { image = "barebox.bin" } // barebox.bin from root of barebox dir + file barebox.bin { image = "barebox-at91sam9263ek.img" } + file zImage { image = "zImage" } + } + + size = 16M + } + + image rootfs.ext4 { + ext4 { + label = "root" + } + mountpoint = "/" + size = 1500M + } + + image SD { + hdimage {} + + partition boot { + partition-type = 0xc + bootable = "true" + image = "boot.vfat" + } + + partition root { + image = "rootfs.ext4" + partition-type = 0x83 + } + + } + +ROMBOOT will load the BOOT.BIN file to internal SRAM that +starts at 0x300000. Maximum size 0x12000 (72 KiB). +When loaded ROMBOOT will remap like this: + +.. code-block:: none + + 0x00000000 0x00000000 + Internal ROM => Internal SRAM + + 0x00300000 0x00400000 + Internal SRAM => Internal ROM + +It is not documented but assumed that ROMBOOT uses the +MMU to remap the addresses. +There seems not to be a dedicated remapping feature that is used. + +Note: For DataFlash and NAND Flash the image is validated. +The first 28 bytes must be valid load PC or PC relative addressing. +Vector 0x6 must include the size of the image (in bytes). +This validation is (according to datasheet) not done for SD Card boots. + +barebox related notes when trying to make it work with PBL enabled + +To let barebox detect the SD card early use: CONFIG_MCI_STARTUP=y + +When PBL (and MULTI_IMAGE) are enabled then barebox creates +a binary with the following structure: + +.. code-block:: none + + +----------------------+ + | PBL (PreBootLoader) | + +----------------------+ + | piggy.o | + |+--------------------+| + ||barebox second stage|| + |+--------------------+| + +----------------------+ + +The PBL contains code from the sections .text_head_entry*, .text_bare_init* and .text* + +``.text_head_entry*:`` +This is the reset vector and exception vectors. Must be the very first in the file + +``.text_bare_init*:`` +Everything in this section, and , is checked at link time. +Size most be less than BAREBOX_MAX_BARE_INIT_SIZE / ARCH_BAREBOX_MAX_BARE_INIT_SIZE + +at91 specify the size of the two sections in exception vector 6 (see above), +if CONFIG_AT91_LOAD_BAREBOX_SRAM is defined. +I think this is because some at91 variants have only very limited SRAM size, +and we copy only a minimal part to the SRAM. The remaining part is then +executed in-place. +For at91sam9263 we have a large SRAM so there is room for the full bootstrap binary. -- 2.12.0 _______________________________________________ barebox mailing list barebox@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/barebox
