A single ESP32-S2’s flash can contain multiple apps, as well as many different kinds of data (calibration data, filesystems, parameter storage, etc). For this reason a partition table is flashed to (default offset) 0x8000 in the flash.
The partition table length is 0xC00 bytes, as we allow a maximum of 95 entries. An MD5 checksum, used for checking the integrity of the partition table at runtime, is appended after the table data. Thus, the partition table occupies an entire flash sector, which size is 0x1000 (4 KB). As a result, any partition following it must be at least located at (default offset) + 0x1000.
Each entry in the partition table has a name (label), type (app, data, or something else), subtype and the offset in flash where the partition is loaded.
The simplest way to use the partition table is to open the project configuration menu (
idf.py menuconfig) and choose one of the simple predefined partition tables under CONFIG_PARTITION_TABLE_TYPE:
“Single factory app, no OTA”
“Factory app, two OTA definitions”
In both cases the factory app is flashed at offset 0x10000. If you execute idf.py partition-table then it will print a summary of the partition table.
Built-in Partition Tables
Here is the summary printed for the “Single factory app, no OTA” configuration:
# ESP-IDF Partition Table # Name, Type, SubType, Offset, Size, Flags nvs, data, nvs, 0x9000, 0x6000, phy_init, data, phy, 0xf000, 0x1000, factory, app, factory, 0x10000, 1M,
At a 0x10000 (64 KB) offset in the flash is the app labelled “factory”. The bootloader will run this app by default.
There are also two data regions defined in the partition table for storing NVS library partition and PHY init data.
Here is the summary printed for the “Factory app, two OTA definitions” configuration:
# ESP-IDF Partition Table # Name, Type, SubType, Offset, Size, Flags nvs, data, nvs, 0x9000, 0x4000, otadata, data, ota, 0xd000, 0x2000, phy_init, data, phy, 0xf000, 0x1000, factory, app, factory, 0x10000, 1M, ota_0, app, ota_0, 0x110000, 1M, ota_1, app, ota_1, 0x210000, 1M,
There are now three app partition definitions. The type of the factory app (at 0x10000) and the next two “OTA” apps are all set to “app”, but their subtypes are different.
There is also a new “otadata” slot, which holds the data for OTA updates. The bootloader consults this data in order to know which app to execute. If “ota data” is empty, it will execute the factory app.
Creating Custom Tables
If you choose “Custom partition table CSV” in menuconfig then you can also enter the name of a CSV file (in the project directory) to use for your partition table. The CSV file can describe any number of definitions for the table you need.
The CSV format is the same format as printed in the summaries shown above. However, not all fields are required in the CSV. For example, here is the “input” CSV for the OTA partition table:
# Name, Type, SubType, Offset, Size, Flags nvs, data, nvs, 0x9000, 0x4000 otadata, data, ota, 0xd000, 0x2000 phy_init, data, phy, 0xf000, 0x1000 factory, app, factory, 0x10000, 1M ota_0, app, ota_0, , 1M ota_1, app, ota_1, , 1M nvs_key, data, nvs_keys, , 0x1000
Whitespace between fields is ignored, and so is any line starting with # (comments).
Each non-comment line in the CSV file is a partition definition.
The “Offset” field for each partition is empty. The gen_esp32part.py tool fills in each blank offset, starting after the partition table and making sure each partition is aligned correctly.
Name field can be any meaningful name. It is not significant to the ESP32-S2. The maximum length of names is 16 bytes, including one null terminator. Names longer than the maximum length will be truncated.
Partition type field can be specified as
app (0x00) or
data (0x01). Or it can be a number 0-254 (or as hex 0x00-0xFE). Types 0x00-0x3F are reserved for ESP-IDF core functions.
If your app needs to store data in a format not already supported by ESP-IDF, then please add a custom partition type value in the range 0x40-0xFE.
esp_partition_type_t for the enum definitions for
static const esp_partition_type_t APP_PARTITION_TYPE_A = (esp_partition_type_t)0x40;
The ESP-IDF bootloader ignores any partition types other than
app (0x00) and
The 8-bit SubType field is specific to a given partition type. ESP-IDF currently only specifies the meaning of the subtype field for
data partition types.
esp_partition_subtype_t for the full list of subtypes defined by ESP-IDF, including the following:
When type is
app, the SubType field can be specified as
factory(0x00) is the default app partition. The bootloader will execute the factory app unless there it sees a partition of type data/ota, in which case it reads this partition to determine which OTA image to boot.
OTA never updates the factory partition.
If you want to conserve flash usage in an OTA project, you can remove the factory partition and use
ota_15(0x1F) are the OTA app slots. When OTA is in use, the OTA data partition configures which app slot the bootloader should boot. When using OTA, an application should have at least two OTA application slots (
ota_1). Refer to the OTA documentation for more details.
test(0x20) is a reserved subtype for factory test procedures. It will be used as the fallback boot partition if no other valid app partition is found. It is also possible to configure the bootloader to read a GPIO input during each boot, and boot this partition if the GPIO is held low, see Boot from Test Firmware.
When type is
data, the subtype field can be specified as
nvs(0x02), nvs_keys (0x04), or a range of other component-specific subtypes (see
phy(1) is for storing PHY initialisation data. This allows PHY to be configured per-device, instead of in firmware.
In the default configuration, the phy partition is not used and PHY initialisation data is compiled into the app itself. As such, this partition can be removed from the partition table to save space.
To load PHY data from this partition, open the project configuration menu (
idf.py menuconfig) and enable CONFIG_ESP_PHY_INIT_DATA_IN_PARTITION option. You will also need to flash your devices with phy init data as the esp-idf build system does not do this automatically.
nvs(2) is for the Non-Volatile Storage (NVS) API.
NVS is used to store per-device PHY calibration data (different to initialisation data).
NVS is used to store Wi-Fi data if the esp_wifi_set_storage(WIFI_STORAGE_FLASH) initialization function is used.
The NVS API can also be used for other application data.
It is strongly recommended that you include an NVS partition of at least 0x3000 bytes in your project.
If using NVS API to store a lot of data, increase the NVS partition size from the default 0x6000 bytes.
nvs_keys(4) is for the NVS key partition. See Non-Volatile Storage (NVS) API for more details.
It is used to store NVS encryption keys when NVS Encryption feature is enabled.
The size of this partition should be 4096 bytes (minimum partition size).
There are other predefined data subtypes for data storage supported by ESP-IDF. These include:
coredump(0x03) is for storing core dumps while using a custom partition table CSV file. See Core Dump for more details.
efuse(0x05) is for emulating eFuse bits using Virtual eFuses.
undefined(0x06) is implicitly used for data partitions with unspecified (empty) subtype, but it is possible to explicitly mark them as undefined as well.
fat(0x81) is for FAT Filesystem Support.
spiffs(0x82) is for SPIFFS Filesystem.
If the partition type is any application-defined value (range 0x40-0xFE), then
subtypefield can be any value chosen by the application (range 0x00-0xFE).
Extra Partition SubTypes
A component can define a new partition subtype by setting the
EXTRA_PARTITION_SUBTYPES property. This property is a CMake list, each entry of which is a comma separated string with
<type>, <subtype>, <value> format. The build system uses this property to add extra subtypes and creates fields named
esp_partition_subtype_t. The project can use this subtype to define partitions in the partitions table CSV file and use the new fields in
Offset & Size
The offset represents the partition address in the SPI flash, which sector size is 0x1000 (4 KB). Thus, the offset must be a multiple of 4 KB.
Partitions with blank offsets in the CSV file will start after the previous partition, or after the partition table in the case of the first partition.
Partitions of type
app have to be placed at offsets aligned to 0x10000 (64 K). If you leave the offset field blank,
gen_esp32part.py will automatically align the partition. If you specify an unaligned offset for an app partition, the tool will return an error.
Sizes and offsets can be specified as decimal numbers, hex numbers with the prefix 0x, or size multipliers K or M (1024 and 1024*1024 bytes).
If you want the partitions in the partition table to work relative to any placement (CONFIG_PARTITION_TABLE_OFFSET) of the table itself, leave the offset field (in CSV file) for all partitions blank. Similarly, if changing the partition table offset then be aware that all blank partition offsets may change to match, and that any fixed offsets may now collide with the partition table (causing an error).
Only one flag is currently supported,
encrypted. If this field is set to
encrypted, this partition will be encrypted if Flash Encryption is enabled.
app type partitions will always be encrypted, regardless of whether this flag is set or not.
Generating Binary Partition Table
The partition table which is flashed to the ESP32-S2 is in a binary format, not CSV. The tool partition_table/gen_esp32part.py is used to convert between CSV and binary formats.
If you configure the partition table CSV name in the project configuration (
idf.py menuconfig) and then build the project or run
idf.py partition-table, this conversion is done as part of the build process.
To convert CSV to Binary manually:
python gen_esp32part.py input_partitions.csv binary_partitions.bin
To convert binary format back to CSV manually:
python gen_esp32part.py binary_partitions.bin input_partitions.csv
To display the contents of a binary partition table on stdout (this is how the summaries displayed when running
idf.py partition-table are generated:
python gen_esp32part.py binary_partitions.bin
Partition Size Checks
The ESP-IDF build system will automatically check if generated binaries fit in the available partition space, and will fail with an error if a binary is too large.
Currently these checks are performed for the following binaries:
Bootloader binary must fit in space before partition table (see Bootloader Size).
App binary should fit in at least one partition of type “app”. If the app binary does not fit in any app partition, the build will fail. If it only fits in some of the app partitions, a warning is printed about this.
Although the build process will fail if the size check returns an error, the binary files are still generated and can be flashed (although they may not work if they are too large for the available space.)
The binary format of the partition table contains an MD5 checksum computed based on the partition table. This checksum is used for checking the integrity of the partition table during the boot.
The MD5 checksum generation can be disabled by the
--disable-md5sum option of
gen_esp32part.py or by the CONFIG_PARTITION_TABLE_MD5 option.
Flashing the Partition Table
idf.py partition-table-flash: will flash the partition table with esptool.py.
idf.py flash: Will flash everything including the partition table.
A manual flashing command is also printed as part of
idf.py partition-table output.
Note that updating the partition table does not erase data that may have been stored according to the old partition table. You can use
idf.py erase-flash (or
esptool.py erase_flash) to erase the entire flash contents.
Partition Tool (
The component partition_table provides a tool parttool.py for performing partition-related operations on a target device. The following operations can be performed using the tool:
reading a partition and saving the contents to a file (read_partition)
writing the contents of a file to a partition (write_partition)
erasing a partition (erase_partition)
retrieving info such as name, offset, size and flag (“encrypted”) of a given partition (get_partition_info)
The tool can either be imported and used from another Python script or invoked from shell script for users wanting to perform operation programmatically. This is facilitated by the tool’s Python API and command-line interface, respectively.
Before anything else, make sure that the parttool module is imported.
import sys import os idf_path = os.environ["IDF_PATH"] # get value of IDF_PATH from environment parttool_dir = os.path.join(idf_path, "components", "partition_table") # parttool.py lives in $IDF_PATH/components/partition_table sys.path.append(parttool_dir) # this enables Python to find parttool module from parttool import * # import all names inside parttool module
The starting point for using the tool’s Python API to do is create a ParttoolTarget object:
# Create a partool.py target device connected on serial port /dev/ttyUSB1 target = ParttoolTarget("/dev/ttyUSB1")
The created object can now be used to perform operations on the target device:
# Erase partition with name 'storage' target.erase_partition(PartitionName("storage")) # Read partition with type 'data' and subtype 'spiffs' and save to file 'spiffs.bin' target.read_partition(PartitionType("data", "spiffs"), "spiffs.bin") # Write to partition 'factory' the contents of a file named 'factory.bin' target.write_partition(PartitionName("factory"), "factory.bin") # Print the size of default boot partition storage = target.get_partition_info(PARTITION_BOOT_DEFAULT) print(storage.size)
The partition to operate on is specified using PartitionName or PartitionType or PARTITION_BOOT_DEFAULT. As the name implies, these can be used to refer to partitions of a particular name, type-subtype combination, or the default boot partition.
More information on the Python API is available in the docstrings for the tool.
The command-line interface of parttool.py has the following structure:
parttool.py [command-args] [subcommand] [subcommand-args] - command-args - These are arguments that are needed for executing the main command (parttool.py), mostly pertaining to the target device - subcommand - This is the operation to be performed - subcommand-args - These are arguments that are specific to the chosen operation
# Erase partition with name 'storage' parttool.py --port "/dev/ttyUSB1" erase_partition --partition-name=storage # Read partition with type 'data' and subtype 'spiffs' and save to file 'spiffs.bin' parttool.py --port "/dev/ttyUSB1" read_partition --partition-type=data --partition-subtype=spiffs --output "spiffs.bin" # Write to partition 'factory' the contents of a file named 'factory.bin' parttool.py --port "/dev/ttyUSB1" write_partition --partition-name=factory --input "factory.bin" # Print the size of default boot partition parttool.py --port "/dev/ttyUSB1" get_partition_info --partition-boot-default --info size
More information can be obtained by specifying –help as argument:
# Display possible subcommands and show main command argument descriptions parttool.py --help # Show descriptions for specific subcommand arguments parttool.py [subcommand] --help