A cute Python utility to communicate with the ROM bootloader in Espressif ESP8266. It is intended to be a simple, platform independent, open source replacement for XTCOM.
esptool.py depends on pySerial for serial communication with the target device.
If you choose to install esptool.py system-wide by running python setup.py install, then this will be taken care of automatically.
If not using setup.py, then you'll have to install pySerial manually by running something like pip install pyserial, easy_install pyserial or apt-get install python-serial, depending on your platform. (The official pySerial installation instructions are here).
Use esptool.py -h to see a summary of all available commands and command line options.
To see all options for a particular command, append -h to the command name. ie esptool.py write_flash -h.
The serial port is selected using the -p option, like -p /dev/ttyUSB0 (on unixen like Linux and OSX) or -p COM1
(on Windows).
If using Cygwin on Windows, you have to convert the Windows-style name into an Unix-style path (COM1 -> /dev/ttyS0, and so on).
The default esptool.py baud rate is 115200bps. Different rates may be set using -b 921600 (or another baudrate of your choice). Baudrate can also be specified using ESPTOOL_BAUD environment variable. This can speed up data transfers.
The ESP8266 bootloader auto-bauds, so it will automatically match the baud rate used by esptool.py.
Most hardware configurations will work with -b 230400, some with -b 460800 and/or -b 921600.
You can also choose 74880, which is the usual baud rate used by the ESP8266 to output boot log information.
The elf2image command converts an ELF file (from compiler/linker output) into the binary blobs to be flashed:
esptool.py elf2image my_app.elf
This command does not require a serial connection.
The default command output is two binary files: my_app.elf-0x00000.bin and my_app.elf-0x40000.bin. You can alter the firmware file name prefix using the --output/-o option.
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 elf2image --version=2 -o my_app-ota.bin my_app.elf
The binaries from elf2image or make_image can be sent to the ESP8266 via the serial write_flash command:
esptool.py write_flash 0x00000 my_app.elf-0x00000.bin 0x40000 my_app.elf-0x40000.bin
Or, for a "version 2" image, a single argument:
esptool.py write_flash 0x2000 my_app-ota.bin
The arguments are one or more pairs of offset (address) and file name. The file names created by elf2image include the flash offsets for version 1. For version 2, the bootloader and linker script you are using determines the flash offset.
See the Flash Modes and Troubleshooting sections for more useful information about this command.
You can verify an image in the flash by passing the --verify option to the write_flash command, or by using the standalone verify_flash command:
./esptool.py verify_flash 0x40000 my_app.elf-0x40000.bin
Verification is not always necessary, the bootloader serial protocol includes a checksum and this is usually enough to guarantee accurate flashing.
NOTE: esptool.py may update the first 16 bytes (offset 0) of the ESP8266 flash when writing (see Flash modes), to set the provided flash mode and flash size parameters. If this happens then the standalone verify_flash command may fail on these bytes (write_flash --verify accounts for this).
You can also manually assemble a firmware image from binary segments (such as those extracted from objcopy), like this:
esptool.py make_image -f app.text.bin -a 0x40100000 -f app.data.bin -a 0x3ffe8000 -f app.rodata.bin -a 0x3ffe8c00 app.flash.bin
This command does not require a serial connection.
The dump_mem command will dump a region from the ESP8266 memory space. For example, to dump the ROM (64 KiB) from the chip:
esptool.py dump_mem 0x40000000 65536 iram0.bin
esptool.py read_mac
esptool.py flash_id
Refer to flashrom source code for flash chip manufacturer name and part number.
esptool.py chip_id
This is the same as the output of the system_get_chip_id() SDK function. The chip ID is four bytes long, the lower three bytes are the final bytes of the MAC address. The upper byte is zero on most (all?) ESP8266s.
The ESP8266 ROM serial bootloader uses a 3.3V UART serial connection. Many ESP8266 development boards make the serial connections for you onboard.
However, if you are wiring the ESP8266 yourself to a USB/Serial adapter or similar then the following connections must be made:
| ESP8266 Pin | Serial Port Pin |
|---|---|
| TX (aka GPIO1) | RX (receive) |
| RX (aka GPIO3) | TX (transmit) |
| Ground | Ground |
Note that TX (transmit) on the ESP8266 is connected to RX (receive) on the serial port connection, and vice versa.
Do not connect the ESP8266 to 5V TTL serial adapters, and especially not to high voltage RS-232 adapters! 3.3v serial only!
The ESP8266 has to be reset in a certain way in order to launch the serial bootloader.
On some development boards (including NodeMCU, WeMOS, HUZZAH Feather), esptool.py can automatically trigger a reset into the serial bootloader - in which case you don't need to read this section.
For everyone else, three things must happen to enter the serial bootloader - a reset, required pins set correctly, and GPIO0 pulled low:
The ESP8266 chooses the boot mode each time it resets. A reset event can happen in one of several ways:
- Power applied to ESP8266.
- The nRESET pin was low and is pulled high.
- The CH_PD pin ("enable") was low and is pulled high.
The nRESET and ENABLE pins must both be pulled high.
The following ESP8266 pins must be pulled high/low for either normal or serial bootloader operation. Most development boards or modules make these connections already, internally:
| GPIO | Must Be Pulled |
|---|---|
| 15 | Low/GND (directly, or with a resistor) |
| 2 | High/VCC (always use a resistor) |
If these pins are set differently to shown, nothing on the ESP8266 will work as expected. See this wiki page to see what boot modes are enabled for different pin combinations.
GPIO2 should always use a pullup resistor to VCC, not a direct connection. This is because it is configured as an output by the boot ROM. If GPIO15 is unused then it can be connected directly to ground, but it's safest to use a pulldown resistor here as well.
The ESP8266 will enter the serial bootloader when GPIO0 is held low on reset. Otherwise it will run the program in flash.
| GPIO0 Input | Mode |
|---|---|
| Low/GND | ROM serial bootloader for esptool.py |
| High/VCC | Normal execution mode |
Many configurations use a "Flash" button that pulls GPIO0 low when pressed.
esptool.py can automatically enter the bootloader on many boards by using only the RTS and DTR modem status lines.
Make the following connections for esptool.py to automatically enter the bootloader:
| ESP8266 Pin | Serial Pin |
|---|---|
| CH_PD ("enable") or nRESET | RTS |
| GPIO0 | DTR |
Note that some serial terminal programs (not esptool.py) will assert both RTS and DTR when opening the serial port, pulling them low together and holding the ESP8266 in reset. If you've wired RTS to the ESP8266 then you should disable RTS/CTS "hardware flow control" in the program. Development boards like NodeMCU use additional circuitry to avoid this problem - if both RTS and DTR are asserted together, this doesn't reset the chip.
write_flash and some other comands accept command line arguments to set flash mode, flash size and flash clock frequency. The ESP8266 needs correct mode, frequency and size settings in order to run correctly - although there is some flexibility.
When flashing at offset 0x0, the first sector of the ESP8266 flash is updated automatically using the arguments passed in.
These set Quad Flash I/O or Dual Flash I/O modes. Valid values are qio, qout, dio, dout. The default is qio. This parameter can also be specified using the environment variable ESPTOOL_FM.
Some ESP8266 modules, including the ESP-12E modules on some (not all) NodeMCU boards, are dual I/O and will only work with --flash_mode dio.
In qio mode, GPIOs 9 and 10 are used for SPI flash communications. If flash mode is set to dio then these pins are available for other purposes.
Size of the SPI flash. Valid values are 4m, 2m, 8m, 16m, 32m, 16m-c1, 32m-c1, 32m-c2 (megabits). The default is 4m (4 megabits, 512 kilobytes.) This parameter can also be specified using the environment variable ESPTOOL_FS.
The ESP8266 SDK stores WiFi configuration at the "end" of flash, and it finds the end using this size. However there is no downside to specifying a smaller flash size than you really have, as long as you don't need to write an image larger than the configured size.
ESP-12, ESP-12E and ESP-12F modules (and boards that use them such as NodeMCU, HUZZAH, etc.) usually have at least 32 megabit (32m i.e. 4MB) flash. You can find the flash size by using the flash_id command and then looking up the ID from the output (see Read SPI flash id).
Clock frequency for SPI flash interactions. Valid values are 40m, 26m, 20m, 80m (MHz). The default is 40m (40MHz). This parameter can also be specified using the environment variable ESPTOOL_FF.
The flash chip on most ESP8266 modules works with 40MHz clock speeds, but you can try lower values if the device won't boot.
ESP8266 problems can be fiddly to troubleshoot. Try the suggestions here if you're having problems:
If you see errors like "Failed to connect to ESP8266" then your ESP8266 is probably not entering the bootloader properly:
- Check you are passing the correct serial port on the command line.
- Check you have permissions to access the serial port, and other software (such as modem-manager on Linux) is not trying to interact with it.
- Check the ESP8266 is receiving 3.3V from a stable power source (see Insufficient Power for more details.)
- Check that all pins are connected as described in Entering the bootloader. Check the voltages at each pin with a multimeter, "high" pins should be close to 3.3V and "low" pins should be close to 0V.
- If you have connected other devices to GPIO0, GPIO2 or GPIO15 then try removing them and see if esptool.py starts working.
- Try using a slower baud rate (
-b 9600is a very slow value that you can use to verify it's not a baud rate problem.)
If flashing fails with random errors part way through, retry with a lower baud rate.
Power stability problems may also cause tihs (see Insufficient Power.)
If esptool.py can flash your module with write_flash but your program doesn't run, try the following:
Some ESP8266 modules only support the dio flash mode. Writing to flash with qio mode will succeed but the ESP8266 can't read it back to run - so nothing happens on boot. Try passing the -fm dio option to write_flash.
The 3.3V power supply for the ESP8266 has to supply large amounts of current (up to 70mA continuous, 200-300mA peak). You also need sufficient capacitance on the power circuit to meet large spikes of power demand.
If you're using a premade development board or module then the built-in power regulator is usually good enough, provided the input power supply is adequate.
It is possible to have a power supply that supplies enough current for the serial bootloader stage, but not enough for normal operation. You may see the 3.3V VCC voltage droop down if you measure it with a multimeter, but you can have problems even if this isn't happening.
Try swapping in a 3.3V supply with a higher current rating, add capacitors to the power line, and/or shorten any 3.3V power wires.
The 3.3V output from FTDI FT232R chips/adapters or Arduino boards do not supply sufficient current to power an ESP8266 (it may seem to work sometimes, but it won't work reliably).
Recent Espressif SDKs use a small software bootloader program. The bootloader in ROM loads this software bootloader from flash, and then it runs the program. This bootloader image has to be flashed at offset 0. If this bootloader is missing then the ESP8266 will not boot.
Refer to your SDK documentation for details regarding which binaries need to be flashed at which offsets.
Use a serial terminal program to view the boot log at 74880bps, see if the program is crashing during early startup or outputting an error message. See Boot log for an example.
There are many serial terminal programs suitable for normal ESP8266 debugging & serial interaction. The pyserial module (which is required for esptool.py) includes one such command line terminal program - miniterm.py. For more details see this page or run miniterm -h.
Note that not every serial program supports the unusual ESP8266 74880bps "boot log" baud rate. Support is especially sparse on Linux. miniterm.py supports this baud rate on all platforms.
The repository wiki contains some technical documentation regarding the serial protocol and file format used by the ROM bootloader. This may be useful if you're developing esptool.py or hacking system internals:
The boot rom writes a log to the UART when booting. The timing is a little bit unusual: 74880 baud
ets Jan 8 2014,rst cause 1, boot mode:(3,7)
load 0x40100000, len 24236, room 16
tail 12
chksum 0xb7
ho 0 tail 12 room 4
load 0x3ffe8000, len 3008, room 12
tail 4
chksum 0x2c
load 0x3ffe8bc0, len 4816, room 4
tail 12
chksum 0x46
csum 0x46
esptool.py was initially created by Fredrik Ahlberg (themadinventor, kongo), and is currently maintained by Fredrik and Angus Gratton (@projectgus). It has also received improvements from many members of the ESP8266 community - including pfalcon, tommie, 0ff and george-hopkins.
This document and the attached source code is released under GPLv2.