Hi experts,
The TRM says that based on the boot mode pins we can boot in raw mode from a sd card without a filesystem. However, it doesn't specify where that image should be written. should it be written at address 0 of the sd card? or is it after things like MBR table, etc. I was under the impression that all storage devices should have a generic thing like MBR or something at the beginning so that different filesystems could be found but I may be wrong. please let me know the address that ROM code looks to load an image in raw mode and how does it work with things like MBR. (should be before or after the image)
this is what the term says :
5.4.3.1 SD Card Bootloader Operation SD Card boot is only available on Port 1 of the MMCSD controller (MMCSD1). The IOs on this port support both 1.8V and 3.3V operation, as well as dynamic voltage change. Thus, this port can support initial operation at 3.3V and remain at this voltage for legacy SD Cards, or support initial operation at 3.3V and change to 1.8V after ROM boot for UHS-I SD Cards. The ROM will boot from SD cards using one of these methods: • User Data Area (UDA) in raw mode • User Data Area (UDA) in filesystem mode The ROM is capable of booting from any size SD card because the MMCSD controller is responsible for addressing. Only single data rate with backward compatible interface timing is supported. The MMCSD module depends on proper voltage level on the SD card detect signal (SDCD). If SDCD=1, the ROM will assume the card is not present and will fail the boot mode.The SDCD must be 0 for the ROM to continue to attempt to boot. Card detect using DAT3 is not supported. If the card is detected, the initial discovery phase is performed: www.ti.com Initialization SPRUIV7A – MAY 2022 – REVISED NOVEMBER 2022 Submit Document Feedback AM62x Processors Silicon Revision 1.0 Texas Instruments Families of Products 2475 Copyright © 2022 Texas Instruments Incorporated 1. Send CMD 0. (GO IDLE, both for MMC and SD) 2. Send CMD 55. If the card responds then the card type is assumed to be SD. On timeout the code sends CMD 1. If there is a response then the card type is MMC. The ROM Code will start reading from the MMCSD memory boot sector, or filesystem, as specified by the BOOTMODE pins. Only FAT32 and FAT16 formats are supported in filesystem mode. It will continue reading data from the memory and storing it in internal RAM until a complete image has been read. In RAW mode only, the ROM supports a redundant image at offset 0x400000 in case the initial image fails to be recognized. When the complete image has been read and found in good integrity, the ROM Code will branch to the address defined in the Boot Info field of the boot header.
