STM32MP257F-DK¶

1. Board Identification¶

Identifier: STM32MP257F-DK

Yocto MACHINE:

stm32mp25-disco-welma

Documentation:

https://www.st.com/en/microcontrollers-microprocessors/stm32mp257f.html

Features:

MPU: STM32MP257f dual ARM Cortex‑A35 64-bit + ARM Cortex‑M33 32-bit
3D GPU up to 900 MHz
NPU up to 900 MHz
RAM: up to 4 GB DDR
Two Octo-SPI memory interfaces
1-Gbit/s Ethernet (RGMII)
x2 USB 2.0 high speed
Wi-Fi 802.11b/g/n
BLE v4.1
Dual-lane MIPI CSI-2 camera module expansion connector
HDMI
LVDS

2. Boot Sequence¶

The boot sequence from an SD card, as follows:

The ROM Code loads TF-A (BL2, FSBL) from the first GPT partition (raw) into SRAM (System RAM inside MPU), and starts it.
TF-A:
Initializes DRAM (used in the following steps)
Loads the FIP container (SSBL) from the partition named "fip"
Launches OP-TEE (BL32)
OP-TEE launches U-Boot (BL33) (in DRAM)
U-Boot starts the kernel
The kernel mounts the initial ram file system (initramfs) and starts Init

Reference: Trusted Firmware-A

Glossary:¶

FSBL: First Stage Boot Loader
SSBL: Second Stage Boot Loader
DRAM: Dynamic RAM, external to the MPU
TF-A: Trusted Firmware-A

3. First installation¶

There are two options for installing software on the board:

Flashing the SD card on a PC, as explained in the quick start.
Using DFU mode and TFTP, as explained in this section.

First Step: Get U-Boot running in RAM¶

Set the boot mode pins, to make the ROM Code start in mode DFU over USB:
- BOOT0 OFF
- BOOT1 OFF
- BOOT2 OFF
- BOOT3 OFF

'OFF' is considered when switch is pushed OPEN position and is 'ON' otherwise (see picture below)

Connect your cables between the board and the PC:
- Power and Serial port (USB PWR STLINK)
- USB OTG (USB DRD)

Have the board load and execute TF-A / OP-TEE / U-Boot in RAM through the dfu-util tools:

  $ DEPLOY_DIR_IMAGE=tmp/deploy/images/stm32mp25-disco-welma
  # Download phase 0x1 by ROM code is the FSBL (TF-A BL2)
  $ dfu-util -a 0 -D $DEPLOY_DIR_IMAGE/arm-trusted-firmware/tf-a-stm32mp257f-dk-optee-programmer-usb_signed.stm32
  # DFU detach to request an FSBL start
  $ dfu-util -a 0 -e
  # Download phase 0x2 by FSBL is the FIP file including the DDR settings
  $ dfu-util -a 0 -D $DEPLOY_DIR_IMAGE/fip/fip-stm32mp257f-dk-ddr-optee-programmer-usb_signed.bin
  # DFU detach to request handle DDR initalization - not required for STM32MP1 series
  $ dfu-util -a 0 -e
  # Download phase 0x3 by FSBL is the FIP file including the SSBL image (U-Boot)
  $ dfu-util -a 1 -D $DEPLOY_DIR_IMAGE/fip/fip-stm32mp257f-dk-optee-programmer-usb_signed.bin
  # DFU detach to request an SSBL start
  $ dfu-util -a 0 -e

Note

The artifact file names may change depending on the version of Yocto you have chosen. Please check your DEPLOYDIR to use the correct file names.

Second Step: Install Welma on the eMMC using TFTP¶

Connect your cables between the board and the PC:
Serial port ST-LINK
Ethernet

Take control of U-Boot, download the eMMC image via TFTP and write it to its destination:

STM32MP> setenv ipaddr 169.254.142.1; setenv serverip 169.254.142.224;
STM32MP> tftp welma/welma-image-minimal-stm32mp25-disco-welma.wic.gz
STM32MP> gzwrite mmc 1 $loadaddr $filesize

Since the ROM code in the STM32MP25 only supports booting from eMMC hardware partitions, TF-A binary must be installed in eMMC boot partitions 1 and 2:

STM32MP> tftp welma/tf-a-stm32mp257f-dk-optee-emmc_signed.stm32
STM32MP> setexpr blkcnt $filesize + 0x1ff
STM32MP> setexpr blkcnt $filesize / 0x200 # blkcnt should me a multiple of 512 (0x200)
STM32MP> mmc dev 1 # select the eMMC
STM32MP> mmc partconf 1 1 1 1 # Select boot1 to be accessed for read/write 
STM32MP> mmc write $loadaddr 0 $blkcnt # write TF-A on boot1
STM32MP> mmc partconf 1 1 2 2 # Select boot2 to be accessed for read/write
STM32MP> mmc write $loadaddr 0 $blkcnt # write TF-A on boot2
STM32MP> mmc partconf 1 1 1 0 # Set boot1 as next boot partition (or 1 1 2 0 for boot2)

Switch the boot mode pins, to make the ROM Code boot from the eMMC:
- BOOT0 OFF
- BOOT1 ON
- BOOT2 OFF
- BOOT3 OFF
Reboot the board
```
STM32MP> reset
```

Regular Boot¶

The regular boot is done from eMMC, as follows:

Set the boot switch to boot from eMMC
Start the board.

Appendix¶

Install Welma using UMS¶

Connect the serial port and OTG
Execute the following command in U-Boot command line to export HW boot1 partition:
```
STM32MP> ums 0 mmc 1.1
```
At this level, the eMMC of the board appears as a connected device to the host machine, named /dev/sdX. It acts as a simple external hard drive plugged on the host USB port.

Copy TF-A to the eMMC card, say /dev/sdc

$ export MACHINE=stm32mp25-disco-welma
$ export DEPLOY_DIR=tmp/deploy/images/$MACHINE/arm-trusted-firmware
$ sudo dd if=$DEPLOY_DIR/tf-a-stm32mp257f-dk-optee-emmc_signed.stm32 of=/dev/sdc conv=fdatasync

Warning

Be sure to use the correct device path in order not to accidentally overwrite another disk

Export HW boot2 partition:
```
STM32MP> ums 0 mmc 1.2
```

Copy TF-A to the eMMC card

$ sudo dd if=$DEPLOY_DIR/tf-a-stm32mp257f-dk-optee-emmc_signed.stm32 of=/dev/sdc conv=fdatasync

Export user data partitions
```
STM32MP> ums 0 mmc 1
```

Copy the generated WIC image to the eMMC card

$ SDIMG=tmp/deploy/images/$MACHINE/welma-image-minimal-dev-$MACHINE.wic
$ gunzip --keep --force $SDIMG.gz
$ sudo dd if="$SDIMG" of=/dev/sdc bs=1M

Set HW boot1 as boot partition
```
STM32MP> mmc partconf 1 1 1 0
```
Switch the boot mode pins, to make the ROM Code boot from the eMMC:
- BOOT0 OFF
- BOOT1 ON
- BOOT2 OFF
- BOOT3 OFF
Reset the board
```
STM32MP> reset
```

Boot from SDCard¶

To boot from an SD card, TF-A and U-Boot must be configured as such. To do this:

Set the BOOTDEVICE_SELECT configuration variable in conf/local.conf to sdcard:
```
BOOTDEVICE_SELECT = "sdcard"
```
Rebuild the image

Plug the SDCard to the host machine and copy the generated WIC image into it, say /dev/sdc

$ SDIMG=tmp/deploy/images/$MACHINE/welma-image-minimal-dev-$MACHINE.wic
$ gunzip --keep --force $SDIMG.gz
$ sudo dd if="$SDIMG" of=/dev/sdc bs=1M

Warning

Be sure to use the correct device path in order not to accidentally overwrite another disk

Switch the boot mode pins, to make the ROM Code boot from the eMMC:
- BOOT0 ON
- BOOT1 OFF
- BOOT2 OFF
- BOOT3 OFF
Power on the board

Hardware Watchdog¶

STM32MP257F-DK uses the ARM SMC hardware Watchdog.

  &arm_wdt {
    timeout-sec = <32>;
    status = "okay";
  };

Started by U-Boot (timeout 32 s)
Serviced by the Linux kernel (as long as no userspace process opens /dev/watchdog0 and takes over)

The STM32MP257x-DK Evaluation boards can boot from different Flash devices (microSD, eMMC, S-NOR...):

Boot mode	Boot 1	Boot 0
USB	0	0
microSD	0	1
eMMC	1	0
Development boot	1	1

The values of the BOOT pins are sampled by boot ROM after a reset.