U-Boot for the Gateworks Ventana Product Family boards This file contains information for the port of U-Boot to the Gateworks Ventana Product family boards. The entire Ventana product family (http://www.gateworks.com/product#ventana) is supported by a single bootloader build by using a common SPL and U-Boot that dynamically determines the characterstics of the board at runtime via information from an EEPROM on the board programmed at the factory and supports all of the various boot mediums available. 1. Secondary Program Loader (SPL) --------------------------------- The i.MX6 has a BOOT ROM PPL (Primary Program Loader) which supports loading an executable image from various boot devices. The Gateworks Ventana board config uses an SPL build configuration. This will build the following artifacts from u-boot source: - SPL - Secondary Program Loader that the i.MX6 BOOT ROM (Primary Program Loader) boots. This detects CPU/DRAM configuration, configures The DRAM controller, loads u-boot.img from the detected boot device, and jumps to it. As this is booted from the PPL, it has an IVT/DCD table. - u-boot.img - The main u-boot core which is u-boot.bin with a image header. 2. Build -------- To build U-Boot for the Gateworks Ventana product family: make gwventana_config make 3. Boot source: --------------- The Gateworks Ventana boards support booting from NAND or micro-SD depending on the board model. The IMX6 BOOT ROM will choose a boot media based on eFUSE settings programmed at the factory. Boards with NAND flash will always boot from NAND, and NAND-less boards will always boot from micro-SD. However, it is possible to use the U-Boot bmode command (or the technique it uses) to essentially bootstrap to another boot media at runtime. 3.1. boot from NAND ------------------- The i.MX6 BOOT ROM expects some structures that provide details of NAND layout and bad block information (referred to as 'bootstreams') which are replicated multiple times in NAND. The number of replications and their spacing (referred to as search stride) is configurable through board strapping options and/or eFUSE settings (BOOT_SEARCH_COUNT / Pages in block from BOOT_CFG2). In addition, the i.MX6 BOOT ROM Flash Configuration Block (FCB) supports two copies of a bootloader in flash in the case that a bad block has corrupted one. The Freescale 'kobs-ng' application from the Freescale LTIB BSP, which runs under Linux and operates on an MTD partition, must be used to program the bootstream in order to setup this flash structure correctly. The Gateworks Ventana boards with NAND flash have been factory programmed such that their eFUSE settings expect 2 copies of the boostream (this is specified by providing kobs-ng with the --search_exponent=1 argument). Once in Linux with MTD support for the NAND on /dev/mtd0 you can program the SPL with: kobs-ng init -v -x --search_exponent=1 SPL The kobs-ng application uses an imximage which contains the Image Vector Table (IVT) and Device Configuration Data (DCD) structures that the i.MX6 BOOT ROM requires to boot. The kobs-ng adds the Firmware Configuration Block (FCB) and Discovered Bad Block Table (DBBT). The SPL build artifact from u-boot is an imximage. The u-boot.img, which is the non SPL u-boot binary appended to a u-boot image header must be programmed in the NAND flash boot device at an offset hard coded in the SPL. For the Ventana boards, this has been chosen to be 14MB. The image can be programmed from either u-boot or Linux: u-boot: Ventana > setenv mtdparts mtdparts=nand:14m(spl),2m(uboot),1m(env),-(rootfs) Ventana > tftp ${loadaddr} u-boot.img && nand erase.part uboot && \ nand write ${loadaddr} uboot ${filesize} Linux: nandwrite /dev/mtd1 u-boot.img The above assumes the default Ventana partitioning scheme which is configured via the mtdparts env var: - spl: 14MB - uboot: 2M - env: 1M - rootfs: the rest This information is taken from: http://trac.gateworks.com/wiki/ventana/bootloader#nand More details about the i.MX6 BOOT ROM can be found in the IMX6 reference manual. 3.1. boot from micro-SD ----------------------- When the IMX6 eFUSE settings have been factory programmed to boot from micro-SD the SPL will be loaded from offset 0x400 (1KB). Once the SPL is booted, it will load and execute U-boot (u-boot.img) from offset 69KB on the micro-SD (defined by CONFIG_SYS_MMCSD_RAW_MODE_U_BOOT_SECTOR). While it is technically possible to enable the SPL to be able to load U-Boot from a file on a FAT/EXT filesystem on the micro-SD, we chose to use raw micro-SD access to keep the code-size and boot time of the SPL down. For these reasons a micro-SD that will be used as an IMX6 primary boot device must be carefully partitioned and prepared. The following shell commands are executed on a Linux host (adjust DEV to the block storage device of your micro-SD): DEV=/dev/sdc # zero out 1MB of device sudo dd if=/dev/zero of=$DEV count=1 bs=1M oflag=sync status=none && sync # copy SPL to 1KB offset sudo dd if=SPL of=$DEV bs=1K seek=1 oflag=sync status=none && sync # copy U-Boot to 69KB offset sudo dd if=u-boot.img of=$DEV bs=1K seek=69 oflag=sync status=none && sync # create a partition table with a single rootfs partition starting at 1MB printf "1,,L\n" | sudo sfdisk --in-order --no-reread -L -uM $DEV && sync # format partition sudo mkfs.ext4 -L root ${DEV}1 # mount the partition sudo udisks --mount ${DEV}1 # extract filesystem sudo tar xvf rootfs.tar.gz -C /media/root # flush and unmount sync && sudo umount /media/root The above assumes the default Ventana micro-SD partitioning scheme - spl : 1KB-69KB (68KB) required by IMX6 BOOT ROM - uboot : 69KB-709KB (640KB) defined by CONFIG_SYS_MMCSD_RAW_MODE_U_BOOT_SECTOR - env : 709KB-965KB (256KB) defined by CONFIG_ENV_MMC_SIZE CONFIG_ENV_MMC_OFFSET_REDUND - rootfs : 1MB- This information is taken from: http://trac.gateworks.com/wiki/ventana/bootloader#microsd More details about the i.MX6 BOOT ROM can be found in the IMX6 reference manual.