Write Binary Data to Flash: write_flash
Binary data can be written to the ESP’s flash chip via the serial
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
--chip argument is optional when writing to flash, esptool will detect the type of chip when it connects to the serial port.
--port argument is documented under Serial Port.
The next arguments to
write_flash are one or more pairs of offset (address) and file name. When generating ESP8266 “version 1” images, the file names created by
elf2image include the flash offsets as part of the file name.
For other types of images, 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.
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.
-e/--erase-all option to erase all flash sectors (not just the write areas) before programming.
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
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):
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.
Read Built-in MAC Address: read_mac
Read SPI Flash ID: flash_id
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
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 ESP8266 elf2image my_app.elf
This command does not require a serial connection.
elf2image also accepts the Flash Modes arguments
--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.
elf2image uses the sections in the ELF file to generate each segment in the binary executable. To use segments (PHDRs) instead, pass the
The default command output for ESP8266 is two binary files:
my_app.elf-0x40000.bin. You can alter the firmware file name prefix using the
elf2image can also produce a “version 2” image file suitable for use with a software bootloader stub such as rboot or the Espressif bootloader program. You can’t flash a “version 2” image without also flashing a suitable bootloader.
esptool.py --chip ESP8266 elf2image --version=2 -o my_app-ota.bin my_app.elf
Output .bin Image Details: image_info
image_info command outputs some information (load addresses, sizes, etc) about a
.bin file created by
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
Merge Binaries for Flashing: merge_bin
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 based on selected output format.
esptool.py --chip ESP8266 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.
merge_bincommand supports the same
--flash_freqoptions as the
write_flashcommand 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
--chipparameter if using these options, as the supported values and the bootloader offset both depend on the chip.
--formatoption will change the format of the output file. For more information about formats see formats description below.
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 a
flash_argsfile in the build directory of a project:
cd build # The build directory of an ESP-IDF project esptool.py --chip ESP8266 merge_bin -o merged-flash.bin @flash_args
RAW Output Format
The output of the command will be in
raw format and gaps between individual files will be filled with 0xFF bytes (same as unwritten flash contents).
Because gaps between the input files are padded with 0xFF bytes, when the merged binary is written then any flash sectors between the individual files will be erased. To avoid this, write the files individually.
--fill-flash-size SIZEoption will pad the merged binary with 0xFF bytes to the full flash specified size, for example
--fill-flash-size 4MBwill create a 4MB binary file.
--target-offset 0xNNNoption will create a merged binary that should be flashed at the specified offset, instead of at offset 0x0.
UF2 Output Format
This command will generate a UF2 (USB Flashing Format) binary. This UF2 file can be copied to a USB mass storage device exposed by another ESP running the ESP USB Bridge project. The bridge MCU will use it to flash the target MCU. This is as simple copying (or “drag-and-dropping”) the file to the exposed disk accessed by a file explorer in your machine.
Gaps between the files will be filled with 0x00 bytes.
--chunk-sizeoption will set what portion of 512 byte block will be used for data. Common value is 256 bytes. By default the largest possible value will be used.
--md5-disableoption will disable MD5 checksums at the end of each block. This can be useful for integration with e.g. tinyuf2.
esptool.py --chip ESP8266 merge_bin --format uf2 -o merged-flash.uf2 --flash_mode dio --flash_size 4MB 0x1000 bootloader.bin 0x8000 partition-table.bin 0x10000 app.bin
The following commands are less commonly used, or only of interest to advanced users. They are documented in the Advanced Commands section: