Basic Commands
Write Binary Data to Flash: write_flash
Binary data can be written to the ESP’s flash chip via the serial write_flash
command:
esptool.py --port COM4 write_flash 0x1000 my_app-0x01000.bin
Multiple flash addresses and file names can be given on the same command line:
esptool.py --port COM4 write_flash 0x00000 my_app.elf-0x00000.bin 0x40000 my_app.elf-0x40000.bin
The --chip
argument is optional when writing to flash, esptool will detect the type of chip when it connects to the serial port.
The --port
argument is documented under Serial Port.
The next arguments to write_flash
are one or more pairs of offset (address) and file name. Consult your SDK documentation to determine the files to flash at which offsets.
Numeric values passed to write_flash (and other commands) can be specified either in hex (ie 0x1000), or in decimal (ie 4096).
See the Troubleshooting section if the write_flash
command is failing, or the flashed module fails to boot.
Setting Flash Mode and Size
You may also need to specify arguments for flash mode and flash size, if you wish to override the defaults. For example:
esptool.py --port /dev/ttyUSB0 write_flash --flash_mode qio --flash_size 32m 0x0 bootloader.bin 0x1000 my_app.bin
Since esptool v2.0, these options are not often needed as the default is to keep the flash mode and size from the .bin
image file. See the Flash Modes section for more details.
Compression
By default, the serial transfer data is compressed for better performance. The -u/--no-compress
option disables this behaviour.
Erasing Flash Before Write
To successfully write data into flash, all 4096-byte memory sectors (the smallest erasable unit) affected by the operation have to be erased first. As a result, when the flashing offset address or the data are not 4096-byte aligned, more memory is erased than actually needed. Esptool will display information about which flash memory sectors will be erased.
Use the -e/--erase-all
option to erase all flash sectors (not just the write areas) before programming.
Bootloader Protection
Flashing into the bootloader region (0x0
-> 0x8000
) is disabled by default if active Secure Boot is detected.
This is a safety measure to prevent accidentally overwriting the secure bootloader, which can ultimately lead to bricking the device.
This behavior can be overridden with the --force
option. Use this only at your own risk and only if you know what you are doing!
Encrypted Flash Protection
Overwriting the encrypted firmware (bootloader, application, etc.) without the --encrypt
option is disabled, if:
Flash Encryption and Secure Download Mode are enabled or
Flash Encryption is enabled but Encrypted Download is disabled (efuse bit
EFUSE_DIS_DOWNLOAD_MANUAL_ENCRYPT
is set).
This is a safety measure to prevent accidentally overwriting the encrypted firmware with a plaintext binary, which can ultimately lead to bricking the device.
This behavior can be overridden with the --force
option. Use this option provided that the flash encryption key is generated external to the device and you could perform the encryption on the host machine.
Flashing an Incompatible Image
esptool.py
checks every binary before flashing. If a valid firmware image is detected, the Chip ID
and Minimum chip revision
fields in its header are compared against the actually connected chip.
If the image turns out to be incompatible with the chip in use or requires a newer chip revision, flashing is stopped.
This behavior can be overridden with the --force
option.
Read Flash Contents: read_flash
The read_flash command allows reading back the contents of flash. The arguments to the command are an address, a size, and a filename to dump the output to. For example, to read a full 2MB of attached flash:
esptool.py -p PORT -b 460800 read_flash 0 0x200000 flash_contents.bin
It is also possible to autodetect flash size by using ALL
as size. The above example with autodetection would look like this:
esptool.py -p PORT -b 460800 read_flash 0 ALL flash_contents.bin
Note
If write_flash
updated the boot image’s flash mode and flash size during flashing then these bytes may be different when read back.
Erase Flash: erase_flash & erase_region
To erase the entire flash chip (all data replaced with 0xFF bytes):
esptool.py erase_flash
To erase a region of the flash, starting at address 0x20000 with length 0x4000 bytes (16KB):
esptool.py erase_region 0x20000 0x4000
The address and length must both be multiples of the SPI flash erase sector size. This is 0x1000 (4096) bytes for supported flash chips.
Flash Protection
Erasing the flash chip is disabled by default if either active Secure Boot or Flash Encryption is detected. This is a safety measure to prevent accidentally deleting the secure bootloader or encrypted data, which can ultimately lead to bricking the device.
This behavior can be overridden with the --force
option. Use this only at your own risk and only if you know what you are doing!
Read Built-in MAC Address: read_mac
esptool.py read_mac
Read SPI Flash ID: flash_id
esptool.py flash_id
Example output:
Manufacturer: e0
Device: 4016
Detected flash size: 4MB
Refer to flashrom source code for flash chip manufacturer name and part number.
Convert ELF to Binary: elf2image
The elf2image
command converts an ELF file (from compiler/linker output) into the binary executable images which can be flashed and then booted into:
esptool.py --chip ESP32-C3 elf2image my_app.elf
This command does not require a serial connection.
elf2image
also accepts the Flash Modes arguments --flash_freq
and --flash_mode
, which can be used to set the default values in the image header. This is important when generating any image which will be booted directly by the chip.
These values can also be overwritten via the write_flash
command, see the write_flash command for details. However, if you want to overwrite these values via the write_flash
command then use the --dont-append-digest
argument of the elf2image
command in order to skip appending a SHA256 digest after the image. The SHA256 digest would be invalidated by rewriting the image header, therefore, it is not allowed.
By default, elf2image
uses the sections in the ELF file to generate each segment in the binary executable. To use segments (PHDRs) instead, pass the --use_segments
option.
For ESP32-C3, elf2image produces a single output binary “image file”. By default this has the same name as the .elf file, with a .bin extension. For example:
esptool.py --chip ESP32-C3 elf2image my_esp_app.elf
In the above example, the output image file would be called my_esp_app.bin
.
Output .bin Image Details: image_info
The image_info
command outputs some information (load addresses, sizes, etc) about a .bin
file created by elf2image
.
To view more information about the image, such as set flash size, frequency and mode, or extended header information, use the --version 2
option. This extended output will become the default in a future major release.
This information corresponds to the headers described in Firmware Image Format.
esptool.py image_info --version 2 my_esp_app.bin
If the given binary file is an application and a valid ESP-IDF application header is detected in the image, specific fields describing the application are also displayed.
If the given binary file is a bootloader and a valid ESP-IDF bootloader header is detected in the image, specific fields describing the bootloader are also displayed.
Merge Binaries for Flashing: merge_bin
The merge_bin
command will merge multiple binary files (of any kind) into a single file that can be flashed to a device later. Any gaps between the input files are padded with 0xFF bytes (same as unwritten flash contents).
For example:
esptool.py --chip ESP32-C3 merge_bin -o merged-flash.bin --flash_mode dio --flash_size 4MB 0x1000 bootloader.bin 0x8000 partition-table.bin 0x10000 app.bin
Will create a file merged-flash.bin
with the contents of the other 3 files. This file can be later be written to flash with esptool.py write_flash 0x0 merged-flash.bin
.
Options:
The
merge_bin
command supports the same--flash_mode
,--flash_size
and--flash_freq
options as thewrite_flash
command to override the bootloader flash header (see above for details). These options are applied to the output file contents in the same way as when writing to flash. Make sure to pass the--chip
parameter if using these options, as the supported values and the bootloader offset both depend on the chip.The
--target-offset 0xNNN
option will create a merged binary that should be flashed at the specified offset, instead of at offset 0x0.The
--fill-flash-size SIZE
option will pad the merged binary with 0xFF bytes to the full flash specified size, for example--fill-flash-size 4MB
will create a 4MB binary file.It is possible to append options from a text file with
@filename
. As an example, this can be conveniently used with the ESP-IDF build system, which produces aflash_args
file in the build directory of a project:
cd build # The build directory of an ESP-IDF project
esptool.py --chip ESP32-C3 merge_bin -o merged-flash.bin @flash_args
Advanced Commands
The following commands are less commonly used, or only of interest to advanced users. They are documented in the Advanced Commands section: