STM32MP15 Flash mapping

Revision as of 14:55, 22 October 2019 by Registered User (→‎eMMC memory mapping)

1. Supported Flash memory technologies[edit source]

The STM32MP15 boards support different kind of Flash memories:

  • SD card on SDMMC interface that is present on EVAL and DISCO boards.
  • eMMC 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[edit source]

The table below lists the partitions defined for STMP32MP15 boards.

(*): the partition size depends on the Flash technology as it should be aligned on the block erase size (256kB for NOR and 512kB for NAND).

Info white.png Information
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.

3. SD card memory mapping[edit source]

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 search the GPT entries which 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.

SD card mapping.png

4. eMMC memory mapping[edit source]

The eMMC 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 eMMC with the layout shown below and to populate each partition.

Info white.png Information
The boot area partition used by the eMMC boot sequence is selected via the EXT_CSD[179] register that is inside the eMMC. 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 eMMC EXT_CSD[179] register to select it.
EMMC mapping.png


5. NOR memory mapping[edit source]

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 eMMC 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
NOR mapping.png


6. NAND memory mapping[edit source]

STM32CubeProgrammer has to be used to prepare the NAND Flash with the layout shown below, and to populate each partition.

NAND mapping.png