SPRUI30H November 2015 – May 2024 DRA745 , DRA746 , DRA750 , DRA756
If the selected booting device is eMMC, then a first attempt to trigger alternative boot operation mode is tried. If the eMMC device replies within a fixed timeout, then the booting image is directly retrieved from one of the possible partitions specified in the local EXT_CSD.BOOT_PARTITION_ENABLE bit field for the eMMC device (this is referred to as the Raw(Boot) mode). Raw(Boot) mode improves the boot time by avoiding the regular eMMC/SD identification phase (usually done at low speed). When the booting image is retrieved, the ROM code continues the boot process.
If the time-out elapses, then the ROM code proceeds with normal identification. SD cards do not support Alternative Boot Operation mode, and therefore are always going through normal identification.
If normal identification succeeds, then it next determines whether the SD card or eMMC device contains a known file system. If the file system is known, then the booting image is extracted from the file system hierarchy. If a file system is not detected, then the Raw(UDA) mode is assumed.
Figure 32-23 is the high level flow chart of the eMMC and SD booting procedure.