STM32MP15 Flash mapping
1 Supported Flash memory technologies
The STM32MP15 boards support different kind of Flash memories:
- SD card on SDMMC interface that is present on EVAL and DISCO boards.
- e•MMC on SDMMC interface that is present on EVAL board only.
- Serial NOR Flash on Dual QSPI interface, that is present on EVAL board only.
- NAND Flash on FMC interface, that is present on EVAL board only.
The next section lists all partitions used on STM32MP15 boards (size, name, content) and the following sections shows how they are mapped on the different types of Flash memories.
2 Flash partitions
The tables below list the partitions defined for STMP32MP15 boards.
|Remaining area||userfs||The user file system contains user data and examples|
|768 MB||rootfs||Linux root file system contains all user space binaries (executable, libraries, …) and kernel modules|
|16 MB||vendorfs||This partition is preferred to the rootfs to put third parties proprietary binaries and ensure that they are not contaminated by any open source licence, such as GPL v3|
|64 MB||bootfs||The boot file system contains:
|2 MB||ssbl||The second stage boot loader (SSBL) is U-Boot, with its device tree blob (dtb) appended at the end|
|256 KB to 512 KB (*)||fsbl||The first stage boot loader is Arm Trusted Firmware (TF-A) or U-Boot Secondary Program Loader (SPL), with its device tree blob (dtb) appended at the end. At least two copies are embedded.|
Note: due to ROM code RAM needs, FSBL payload is limited to 247 KB.
(*): the partition size depends on the flash technology, to be aligned on block erase size of the flash present on the board: NOR (256 KB) / NAND (512 KB)
|Some boards can be equiped with multiple flash devices, like the EVAL board, and all those flashes can be programmed with STM32CubeProgrammer. But caution must be taken for the serial NOR/NAND and SLC NAND because a static bootable MTD partitionning is defined in U-Boot include/configs/stm32mp1.h (look for STM32MP_MTDPARTS), with the consequence that up to 6 MB of space is lost at the beginning of such devices, even if they are not bootable.|
|256 KB (*)||env||This partition is used to store U-Boot environment while booting on NOR flash. For all other flashes, U-Boot environment is stored whether in an EXT4 bootfs partition (e•MMC, SD card) or UBI volumes (NAND).|
|256 KB to 512 KB (*)||teeh||OP-TEE header|
|256 KB to 512 KB (*)||teed||OP-TEE pageable code and data|
|256 KB to 512 KB (*)||teex||OP-TEE pager|
(*): the partition size depends on the Flash technology as it should be aligned on the block erase size of the flash present on the board (256 KB for NOR and 512 KB for NAND).
3 SD card memory mapping
The SD card has to be partitioned with GPT format to be recognized by STM32MP15. The easiest way to achieve this is to use STM32CubeProgrammer.
The ROM code looks for the GPT entries whose the name begins with "fsbl": fsbl1 and fsbl2 for example.
Note: the SD card can be unplugged from the board and inserted into a Linux host computer for direct partitionning with Linux utilities and access to the bootfs, rootfs and userfs partitions. The file system is Linux EXT4.
4 e•MMC memory mapping
The e•MMC embeds four physical partitions:
- Boot area partition 1: one copy of the FSBL.
- Boot area partition 2: one copy of the FSBL.
- User data area: formatted with GPT partitioning and used to store all remaining partitions.
- Replay Protected Memory Block (RPMB): not shown in the figure below, since not involved in the current boot chain.
STM32CubeProgrammer has to be used to prepare the e•MMC with the layout shown below and to populate each partition.
|The boot area partition used by the e•MMC boot sequence is selected via the EXT_CSD register that is inside the e•MMC. The STM32CubeProgrammer execution is concluded with the selection of the last written partition from the flashlayout file, so the partition 2, typically. The other copy is never used as long as the user does not explicitely change the e•MMC EXT_CSD register to select it.|
5 NOR memory mapping
NOR Flash being expensive, their size is usually limited to the minimum, allowing to store only the bootloaders. The system files (bootfs, rootfs and userfs) are usually stored in another Flash memory: like the SD card in OpenSTLinux distribution.
STM32CubeProgrammer has to be used to prepare the NOR Flash and the SD card with the layout shown below and to populate each partition.
It is possible to use an e•MMC card or NAND rather than a SD card as second level Flash memory. It requires to change:
- the Flash memory layout, using STM32CubeProgrammer in order to write the rootfs and userfs to the targeted Flash memory
- the Linux kernel parameters, using U-Boot, in order to indicate where the rootfs and userfs have to be mounted
6 NAND memory mapping
STM32CubeProgrammer has to be used to prepare the NAND Flash with the layout shown below, and to populate each partition.
Flash memories combine high density and cost effectiveness of EPROMs with the electrical erasability of EEPROMs.
Random Access Memory
Second Stage Boot Loader
Trusted Firmware for Arm Cortex-A
Secondary Program Loader, Also known as U-Boot SPL
Read Only Memory
First Stage Boot Loader
Single-Level Cell is a kind of NAND flash
Memory Technology Device
Open Portable Trusted Execution Environment
GUID Partition Table