MCUXpresso SDK Documentation
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blhost

blhost#

blhost is NXP’s command-line host tool for communicating with the RT2660 Boot ROM in serial download mode (SDP).

Prerequisites#

  1. Install Python 3.8 or later.

  2. Obtain the blhost tool. blhost is distributed as part of NXP’s Secure Provisioning SDK (SPSDK) / MCUXpresso Secure Provisioning Tool, available from the NXP website. Install SPSDK (pip install spsdk) or download the standalone tool package from NXP, then use the following supporting files (helper scripts and test image ship with the SDK example resources for eMMC boot):

    • blhost / blhost.exe – the blhost executable (from SPSDK / the NXP tool package).

    • write_emmc.py, read_emmc.py, erase_emmc.py – Python helper scripts for eMMC read/write/erase.

    • write_fuse_boot_cfg0.py – programs BOOT_CFG0 to configure eMMC boot mode.

    • read_fuse_boot_cfg0.py – reads the current BOOT_CFG0 value.

    • ahab_serial_flashloader_plain_secp521r1.bin – serial flashloader required by Python helper scripts.

    • eMMC-bootable-hello_world.bin – pre-built test image for quick eMMC boot verification.

  3. Ensure blhost (blhost.exe) is on your system PATH, or run commands from its install directory.

  4. Set the MIMXRT2660-EVK boot switch to serial download mode (0b10, SDP MODE).

  5. Reset the board – the Boot ROM enters SDP and waits for a host connection.

  6. Identify the COM port (USB-CDC or UART) that blhost should connect to.

Verify connectivity:

blhost -p COM35 -- get-property 1

Expected output:

Ping responded in 1 attempt(s)
Inject command 'get-property'
Response status = 0 (0x0) Success.
Response word 1 = 1258487809 (0x4b030001)
Current Version = K3.0.1

Note: on Linux, use blhost instead of blhost.exe and adapt the COM port to a device path such as /dev/ttyUSB0.

Configuring BOOT_CFG0 for eMMC boot#

Warning: fuse programming is irreversible. Do not execute if BOOT_CFG0 is already programmed to the correct value.

Two scripts are provided for BOOT_CFG0 operations:

  • read_fuse_boot_cfg0.py – reads BOOT_CFG0 (fuse index 0x18). The current value is shown in Response word 2 of the output.

  • write_fuse_boot_cfg0.py – programs BOOT_CFG0 to a specified value. Requires a flashloader; loads it automatically.

Step 1. Set boot switch to 0b10 (SDP mode) and reset the board.

Step 2. Read BOOT_CFG0 to check the current state before programming:

py read_fuse_boot_cfg0.py -p COM35

Options:

  • -p <COM_PORT> – COM port (default: COM35)

The script runs several blhost commands in sequence. The last step is efuse-read-once and its output shows the current BOOT_CFG0 value (example output with fuse not yet programmed):

>> blhost.exe -p COM35,115200 -- efuse-read-once 0x18
Ping responded in 1 attempt(s)
Inject command 'efuse-read-once'
Response status = 0 (0x0) Success.
Response word 1 = 4 (0x4)
Response word 2 = 0 (0x0)

Response word 2 is the BOOT_CFG0 value. If it already reads 0x00000082, BOOT_CFG0 is already configured for eMMC boot – stop here, no further action is needed.

Note: reset the board to re-enter SDP before the next step.

Step 3. Program BOOT_CFG0 to eMMC boot mode:

py write_fuse_boot_cfg0.py -p COM35 -v 0x00000082

Options:

  • -p <COM_PORT> – COM port (default: COM35)

  • -v <value> – BOOT_CFG0 value to program (0x82 or 0x00000082 = eMMC boot mode for MIMXRT2660-EVK)

Note: reset the board to re-enter SDP before the next step.

Step 4. Read back BOOT_CFG0 to verify:

py read_fuse_boot_cfg0.py -p COM35

Response word 2 should now read 0x00000082.

eMMC operations#

Note: after each operation below, the Boot ROM exits SDP. Reset the board before starting the next operation to re-enter SDP.

Writing an image to eMMC#

Use write_emmc.py to write a bootable image to eMMC. The script handles the full sequence: loading the serial flashloader, configuring eMMC, erasing, and writing the image.

Note: before writing, the script erases a region sized to the image file size rounded up to the next 256 KB boundary.

To enable eMMC POR boot, the image written to eMMC must be a bootable image containing a valid USDHC boot header.

The supporting resources include a pre-built test image eMMC-bootable-hello_world.bin that already contains a valid USDHC boot header and can be used to verify the full flow without building from source.

py write_emmc.py -p COM35 -i eMMC-bootable-hello_world.bin

Options:

  • -p <COM_PORT> – COM port (default: COM35)

  • -i <image.bin> – image file to write (default: eMMC-bootable-hello_world.bin)

After a successful boot, the UART will print:

Boot from eMMC,  Sep 20 2026 18:58:19
Shadow Fuse (BOOT CFG0) = 0x00000082
Reset Type = 0x00000200, Reset Cnt = 2
  Reset Type BIT0 = POR_VBAT    reset
  Reset Type BIT2 = POR_b pin   reset
  Reset Type BIT8 = RESET_b pin reset
  Reset Type BIT9 = Software    reset
main = 0x8800745D, SystemCoreClock = 0x88800000, 999MHz
MCUX SDK version: 2026.09.00
hello world.

Reading from eMMC#

py read_emmc.py -p COM35 -a 0 -n 0x20000 -o emmc.bin

Options:

  • -p <COM_PORT> – COM port (default: COM35)

  • -a <address> – start address

  • -n <size> – number of bytes to read

  • -o <output.bin> – output file

Erasing eMMC#

Note: the script automatically rounds up the erase size to the next 256 KB boundary.

py erase_emmc.py -p COM35 -a 0 -n 0x20000

Options:

  • -p <COM_PORT> – COM port (default: COM35)

  • -a <address> – start address

  • -n <size> – number of bytes to erase

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