Configuration File

esptool.py relies on serial communication when connecting to, reading from, or writing to an ESP chip. To ensure this two-way serial connection works properly, esptool.py is tuned with several pre-defined variables describing the timings and other nuances when sending or receiving data. These variables have been finely tuned to work in absolute majority of environments. However, it is impossible to cover all of the existing combinations of hardware, OS, and drivers. Sometimes little tweaking is necessary to cover even the most extreme edge cases.

These options can be specified in a configuration file. This makes it easy to run esptool.py with custom settings, and also allows for specification of options that are otherwise not available to a user without having to tamper with the source code.

File Location

The default name for a configuration file is esptool.cfg. First, the same directory esptool.py is being run in is inspected.

If a configuration file is not found here, the current user’s OS configuration directory is inspected next:

  • Linux: /home/<user>/.config/esptool/

  • MacOS /Users/<user>/.config/esptool/

  • Windows: c:\Users\<user>\AppData\Local\esptool\

If a configuration file is still not found, the last inspected location is the home directory:

  • Linux: /home/<user>/

  • MacOS /Users/<user>/

  • Windows: c:\Users\<user>\

On Windows, the home directory can be set with the HOME or USERPROFILE environment variables. Therefore, the Windows configuration directory location also depends on these.

A different location for the configuration file can be specified with the ESPTOOL_CFGFILE environment variable, e.g. ESPTOOL_CFGFILE = ~/custom_config.cfg. This overrides the search priorities described above.

esptool.py will read settings from other usual configuration files if no other configuration file is used. It will automatically read from setup.cfg or tox.ini if they exist.

As a result, the order of priority of inspected configuration files is:

  1. a file specified with the ESPTOOL_CFGFILE environment variable

  2. esptool.cfg

  3. setup.cfg

  4. tox.ini

Syntax

An esptool.py configuration file is in .ini file format: it must be introduced by an [esptool] header to be recognized as valid. This section then contains name = value entries. Lines beginning with # or ; are ignored as comments.

Delay and timeout options accept float values, other numeric options are integers. Strings don’t need quotes.

Sample configuration file:

# esptool.cfg file to configure internal settings of esptool
[esptool]
chip_erase_timeout = 140
serial_write_timeout = 8.5
connect_attempts = 7
write_block_attempts = 2
reset_delay = 0.75
# Overriding the default reset sequence to work in an abnormal environment
custom_reset_sequence = D0|R1|W0.1|D1|R0|W0.5|D0

Options

Complete list of configurable options:

Option

Description

Default

timeout

Timeout for most flash operations

3 s

chip_erase_timeout

Timeout for a full chip erase

120 s

max_timeout

The longest any command can run

240 s

sync_timeout

Timeout for syncing with the bootloader

0.1 s

md5_timeout_per_mb

Timeout (per megabyte) for calculating md5sum

8 s

erase_region_timeout_per_mb

Timeout (per megabyte) for erasing a region

30 s

erase_write_timeout_per_mb

Timeout (per megabyte) for erasing and writing data

40 s

mem_end_rom_timeout

Short timeout for ESP_MEM_END

0.2 s

serial_write_timeout

Timeout for serial port write

10 s

connect_attempts

Default number of times to try connection

7

write_block_attempts

Number of times to try writing a data block

3

reset_delay

Time to wait before the boot pin is released after reset

0.05 s

open_port_attempts

Number of attempts to open the port (0 - infinite)

1

custom_reset_sequence

Custom reset sequence for resetting into the bootloader

Custom Reset Sequence

The custom_reset_sequence configuration option allows you to define a reset sequence which will get used when an automatic reset into the serial bootloader is performed.

The sequence is defined with a string in the following format:

  • Consists of individual commands divided by | (e.g. R0|D1|W0.5).

  • Commands (e.g. R0) are defined by a code (R) and an argument (0).

Code

Action

Argument

D

Set DTR control line

1/0

R

Set RTS control line

1/0

U

Set DTR and RTS control lines at the same time (Unix-like systems only)

0,0/0,1 1,0/1,1

W

Wait for N seconds (where N is a float)

N

For example: D0|R1|W0.1|D1|R0|W0.5|D0 represents the following classic reset sequence:

_setDTR(False)  # IO0=HIGH
_setRTS(True)   # EN=LOW, chip in reset
time.sleep(0.1)
_setDTR(True)   # IO0=LOW
_setRTS(False)  # EN=HIGH, chip out of reset
time.sleep(0.05)
_setDTR(False)  # IO0=HIGH, done