IDF Monitor

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IDF Monitor uses the esp-idf-monitor package as a serial terminal program which relays serial data to and from the target device's serial port. It also provides some ESP-IDF-specific features.

IDF Monitor can be launched from an ESP-IDF project by running idf.py monitor.

Keyboard Shortcuts

For easy interaction with IDF Monitor, use the keyboard shortcuts given in the table. These keyboard shortcuts can be customized, for more details see Configuration File section.

Keyboard Shortcut

Action

Description

Ctrl + ]

Exit the program

Ctrl + T

Menu escape key

Press and follow it by one of the keys given below.

  • Ctrl + T

Send the menu character itself to remote

  • Ctrl + ]

Send the exit character itself to remote

  • Ctrl + P

Reset target into bootloader to pause app via RTS and DTR lines

Resets the target into the bootloader using the RTS and DTR lines (if connected). This stops the board from executing the application, making it useful when waiting for another device to start. For additional details, refer to Target Reset into Bootloader.

  • Ctrl + R

Reset target board via RTS

Resets the target board and re-starts the application via the RTS line (if connected).

  • Ctrl + F

Build and flash the project

Pauses idf_monitor to run the project flash target, then resumes idf_monitor. Any changed source files are recompiled and then re-flashed. Target encrypted-flash is run if idf_monitor was started with argument -E.

  • Ctrl + A (or A)

Build and flash the app only

Pauses idf_monitor to run the app-flash target, then resumes idf_monitor. Similar to the flash target, but only the main app is built and re-flashed. Target encrypted-app-flash is run if idf_monitor was started with argument -E.

  • Ctrl + Y

Stop/resume log output printing on screen

Discards all incoming serial data while activated. Allows to quickly pause and examine log output without quitting the monitor.

  • Ctrl + L

Stop/resume log output saved to file

Creates a file in the project directory and the output is written to that file until this is disabled with the same keyboard shortcut (or IDF Monitor exits).

  • Ctrl + I (or I)

Stop/resume printing timestamps

IDF Monitor can print a timestamp in the beginning of each line. The timestamp format can be changed by the --timestamp-format command line argument.

  • Ctrl + H (or H)

Display all keyboard shortcuts

  • Ctrl + X (or X)

Exit the program

Ctrl + C

Interrupt running application

Pauses IDF Monitor and runs GDB project debugger to debug the application at runtime. This requires CONFIG_ESP_SYSTEM_GDBSTUB_RUNTIME option to be enabled.

Any keys pressed, other than Ctrl-] and Ctrl-T, will be sent through the serial port.

ESP-IDF-specific Features

Automatic Address Decoding

Whenever the chip outputs a hexadecimal address that points to executable code, IDF monitor looks up the location in the source code (file name and line number) and prints the location on the next line in yellow.

If an ESP-IDF app crashes and panics, a register dump and backtrace are produced, such as the following:

abort() was called at PC 0x42067cd5 on core 0

Stack dump detected
Core  0 register dump:
MEPC    : 0x40386488  RA      : 0x40386b02  SP      : 0x3fc9a350  GP      : 0x3fc923c0
TP      : 0xa5a5a5a5  T0      : 0x37363534  T1      : 0x7271706f  T2      : 0x33323130
S0/FP   : 0x00000004  S1      : 0x3fc9a3b4  A0      : 0x3fc9a37c  A1      : 0x3fc9a3b2
A2      : 0x00000000  A3      : 0x3fc9a3a9  A4      : 0x00000001  A5      : 0x3fc99000
A6      : 0x7a797877  A7      : 0x76757473  S2      : 0xa5a5a5a5  S3      : 0xa5a5a5a5
S4      : 0xa5a5a5a5  S5      : 0xa5a5a5a5  S6      : 0xa5a5a5a5  S7      : 0xa5a5a5a5
S8      : 0xa5a5a5a5  S9      : 0xa5a5a5a5  S10     : 0xa5a5a5a5  S11     : 0xa5a5a5a5
T3      : 0x6e6d6c6b  T4      : 0x6a696867  T5      : 0x66656463  T6      : 0x62613938
MSTATUS : 0x00001881  MTVEC   : 0x40380001  MCAUSE  : 0x00000007  MTVAL   : 0x00000000

MHARTID : 0x00000000

Stack memory:
3fc9a350: 0xa5a5a5a5 0xa5a5a5a5 0x3fc9a3b0 0x403906cc 0xa5a5a5a5 0xa5a5a5a5 0xa5a5a5a50
3fc9a370: 0x3fc9a3b4 0x3fc9423c 0x3fc9a3b0 0x726f6261 0x20292874 0x20736177 0x6c6c61635
3fc9a390: 0x43502074 0x34783020 0x37363032 0x20356463 0x63206e6f 0x2065726f 0x000000300
3fc9a3b0: 0x00000030 0x36303234 0x35646337 0x3c093700 0x0000002a 0xa5a5a5a5 0x3c0937f48
3fc9a3d0: 0x00000001 0x3c0917f8 0x3c0937d4 0x0000002a 0xa5a5a5a5 0xa5a5a5a5 0xa5a5a5a5e
3fc9a3f0: 0x0001f24c 0x000006c8 0x00000000 0x0001c200 0xffffffff 0xffffffff 0x000000200
3fc9a410: 0x00001000 0x00000002 0x3c093818 0x3fccb470 0xa5a5a5a5 0xa5a5a5a5 0xa5a5a5a56
.....

IDF Monitor adds more details to the dump by analyzing the stack dump:

abort() was called at PC 0x42067cd5 on core 0
0x42067cd5: __assert_func at /builds/idf/crosstool-NG/.build/riscv32-esp-elf/src/newlib/newlib/libc/stdlib/assert.c:62 (discriminator 8)

Stack dump detected
Core  0 register dump:
MEPC    : 0x40386488  RA      : 0x40386b02  SP      : 0x3fc9a350  GP      : 0x3fc923c0
0x40386488: panic_abort at /home/marius/esp-idf_2/components/esp_system/panic.c:367

0x40386b02: rtos_int_enter at /home/marius/esp-idf_2/components/freertos/port/riscv/portasm.S:35

TP      : 0xa5a5a5a5  T0      : 0x37363534  T1      : 0x7271706f  T2      : 0x33323130
S0/FP   : 0x00000004  S1      : 0x3fc9a3b4  A0      : 0x3fc9a37c  A1      : 0x3fc9a3b2
A2      : 0x00000000  A3      : 0x3fc9a3a9  A4      : 0x00000001  A5      : 0x3fc99000
A6      : 0x7a797877  A7      : 0x76757473  S2      : 0xa5a5a5a5  S3      : 0xa5a5a5a5
S4      : 0xa5a5a5a5  S5      : 0xa5a5a5a5  S6      : 0xa5a5a5a5  S7      : 0xa5a5a5a5
S8      : 0xa5a5a5a5  S9      : 0xa5a5a5a5  S10     : 0xa5a5a5a5  S11     : 0xa5a5a5a5
T3      : 0x6e6d6c6b  T4      : 0x6a696867  T5      : 0x66656463  T6      : 0x62613938
MSTATUS : 0x00001881  MTVEC   : 0x40380001  MCAUSE  : 0x00000007  MTVAL   : 0x00000000

MHARTID : 0x00000000

Backtrace:
panic_abort (details=details@entry=0x3fc9a37c "abort() was called at PC 0x42067cd5 on core 0") at /home/marius/esp-idf_2/components/esp_system/panic.c:367
367     *((int *) 0) = 0; // NOLINT(clang-analyzer-core.NullDereference) should be an invalid operation on targets
#0  panic_abort (details=details@entry=0x3fc9a37c "abort() was called at PC 0x42067cd5 on core 0") at /home/marius/esp-idf_2/components/esp_system/panic.c:367
#1  0x40386b02 in esp_system_abort (details=details@entry=0x3fc9a37c "abort() was called at PC 0x42067cd5 on core 0") at /home/marius/esp-idf_2/components/esp_system/system_api.c:108
#2  0x403906cc in abort () at /home/marius/esp-idf_2/components/newlib/abort.c:46
#3  0x42067cd8 in __assert_func (file=file@entry=0x3c0937f4 "", line=line@entry=42, func=func@entry=0x3c0937d4 <__func__.8540> "", failedexpr=failedexpr@entry=0x3c0917f8 "") at /builds/idf/crosstool-NG/.build/riscv32-esp-elf/src/newlib/newlib/libc/stdlib/assert.c:62
#4  0x4200729e in app_main () at ../main/iperf_example_main.c:42
#5  0x42086cd6 in main_task (args=<optimized out>) at /home/marius/esp-idf_2/components/freertos/port/port_common.c:133
#6  0x40389f3a in vPortEnterCritical () at /home/marius/esp-idf_2/components/freertos/port/riscv/port.c:129

To decode each address, IDF Monitor runs the following command in the background:

riscv32-esp-elf-addr2line -pfiaC -e build/PROJECT.elf ADDRESS

If an address is not matched in the app source code, IDF monitor also checks the ROM code. Instead of printing the source file name and line number, only the function name followed by in ROM is displayed:

abort() was called at PC 0x400481c1 on core 0
0x400481c1: ets_rsa_pss_verify in ROM

Stack dump detected
Core  0 register dump:
MEPC    : 0x4038051c  RA      : 0x40383840  SP      : 0x3fc8f6b0  GP      : 0x3fc8b000
0x4038051c: panic_abort at /Users/espressif/esp-idf/components/esp_system/panic.c:452
0x40383840: __ubsan_include at /Users/espressif/esp-idf/components/esp_system/ubsan.c:313

TP      : 0x3fc8721c  T0      : 0x37363534  T1      : 0x7271706f  T2      : 0x33323130
S0/FP   : 0x00000004  S1      : 0x3fc8f714  A0      : 0x3fc8f6dc  A1      : 0x3fc8f712
A2      : 0x00000000  A3      : 0x3fc8f709  A4      : 0x00000001  A5      : 0x3fc8c000
A6      : 0x7a797877  A7      : 0x76757473  S2      : 0x00000000  S3      : 0x3fc8f750
S4      : 0x3fc8f7e4  S5      : 0x00000000  S6      : 0x400481b0  S7      : 0x3c025841
0x400481b0: ets_rsa_pss_verify in ROM
.....

The ROM ELF file is automatically loaded from a location based on the IDF_PATH and ESP_ROM_ELF_DIR environment variables. This can be overridden by calling esp_idf_monitor and providing a path to a specific ROM ELF file: python -m esp_idf_monitor --rom-elf-file [path to ROM ELF file].

Note

Set environment variable ESP_MONITOR_DECODE to 0 or call esp_idf_monitor with specific command line option: python -m esp_idf_monitor --disable-address-decoding to disable address decoding.

Target Reset on Connection

By default, IDF Monitor will reset the target when connecting to it. The reset of the target chip is performed using the DTR and RTS serial lines. To prevent IDF Monitor from automatically resetting the target on connection, call IDF Monitor with the --no-reset option (e.g., idf.py monitor --no-reset). You can also set the environment variable ESP_IDF_MONITOR_NO_RESET to 1 to achieve the same behavior.

Note

The --no-reset option applies the same behavior even when connecting IDF Monitor to a particular port (e.g., idf.py monitor --no-reset -p [PORT]).

Target Reset into Bootloader

IDF Monitor provides the capability to reset a chip into the bootloader using a pre-defined reset sequence that has been tuned to work in most environments. Additionally, users have the flexibility to set a custom reset sequence, allowing for fine-tuning and adaptability to diverse scenarios.

Using Pre-defined Reset Sequence

IDF Monitor's default reset sequence is designed to work seamlessly across a wide range of environments. To trigger a reset into the bootloader using the default sequence, no additional configuration is required.

Custom Reset Sequence

For more advanced users or specific use cases, IDF Monitor supports the configuration of a custom reset sequence using Configuration File. This is particularly useful in extreme edge cases where the default sequence may not suffice.

If you would like to use a custom reset sequence, take a look at the IDF Monitor documentation for more details.

Launching GDB with GDBStub

GDBStub is a useful runtime debugging feature that runs on the target and connects to the host over the serial port to receive debugging commands. GDBStub supports commands such as reading memory and variables, examining call stack frames etc. Although GDBStub is less versatile than JTAG debugging, it does not require any special hardware (such as a JTAG to USB bridge) as communication is done entirely over the serial port.

A target can be configured to run GDBStub in the background by setting the CONFIG_ESP_SYSTEM_GDBSTUB_RUNTIME. GDBStub will run in the background until a Ctrl+C message is sent over the serial port and causes the GDBStub to break (i.e., stop the execution of) the program, thus allowing GDBStub to handle debugging commands.

Furthermore, the panic handler can be configured to run GDBStub on a crash by setting the CONFIG_ESP_SYSTEM_PANIC to GDBStub on panic. When a crash occurs, GDBStub will output a special string pattern over the serial port to indicate that it is running.

In both cases (i.e., sending the Ctrl+C message, or receiving the special string pattern), IDF Monitor will automatically launch GDB in order to allow the user to send debugging commands. After GDB exits, the target is reset via the RTS serial line. If this line is not connected, users can reset their target (by pressing the board's Reset button).

Note

In the background, IDF Monitor runs the following command to launch GDB:

riscv32-esp-elf-gdb -ex "set serial baud BAUD" -ex "target remote PORT" -ex interrupt build/PROJECT.elf :idf_target:`Hello NAME chip`

Output Filtering

IDF monitor can be invoked as idf.py monitor --print-filter="xyz", where --print-filter is the parameter for output filtering. The default value is an empty string, which means that everything is printed. Filtering can also be configured using the ESP_IDF_MONITOR_PRINT_FILTER environment variable.

Note

When using both the environment variable ESP_IDF_MONITOR_PRINT_FILTER and the argument --print-filter, the setting from the CLI argument will take precedence.

Restrictions on what to print can be specified as a series of <tag>:<log_level> items where <tag> is the tag string and <log_level> is a character from the set {N, E, W, I, D, V, *} referring to a level for logging.

For example, --print_filter="tag1:W" matches and prints only the outputs written with ESP_LOGW("tag1", ...) or at lower verbosity level, i.e., ESP_LOGE("tag1", ...). Not specifying a <log_level> or using * defaults to a Verbose level.

Note

Use primary logging to disable at compilation the outputs you do not need through the logging library. Output filtering with the IDF monitor is a secondary solution that can be useful for adjusting the filtering options without recompiling the application.

Your app tags must not contain spaces, asterisks *, or colons : to be compatible with the output filtering feature.

If the last line of the output in your app is not followed by a carriage return, the output filtering might get confused, i.e., the monitor starts to print the line and later finds out that the line should not have been written. This is a known issue and can be avoided by always adding a carriage return (especially when no output follows immediately afterwards).

Examples of Filtering Rules:

  • * can be used to match any tags. However, the string --print_filter="*:I tag1:E" with regards to tag1 prints errors only, because the rule for tag1 has a higher priority over the rule for *.

  • The default (empty) rule is equivalent to *:V because matching every tag at the Verbose level or lower means matching everything.

  • "*:N" suppresses not only the outputs from logging functions, but also the prints made by printf, etc. To avoid this, use *:E or a higher verbosity level.

  • Rules "tag1:V", "tag1:v", "tag1:", "tag1:*", and "tag1" are equivalent.

  • Rule "tag1:W tag1:E" is equivalent to "tag1:E" because any consequent occurrence of the same tag name overwrites the previous one.

  • Rule "tag1:I tag2:W" only prints tag1 at the Info verbosity level or lower and tag2 at the Warning verbosity level or lower.

  • Rule "tag1:I tag2:W tag3:N" is essentially equivalent to the previous one because tag3:N specifies that tag3 should not be printed.

  • tag3:N in the rule "tag1:I tag2:W tag3:N *:V" is more meaningful because without tag3:N the tag3 messages could have been printed; the errors for tag1 and tag2 will be printed at the specified (or lower) verbosity level and everything else will be printed by default.

A More Complex Filtering Example

The following log snippet was acquired without any filtering options:

load:0x40078000,len:13564
entry 0x40078d4c
E (31) esp_image: image at 0x30000 has invalid magic byte
W (31) esp_image: image at 0x30000 has invalid SPI mode 255
E (39) boot: Factory app partition is not bootable
I (568) cpu_start: Pro cpu up.
I (569) heap_init: Initializing. RAM available for dynamic allocation:
I (603) cpu_start: Pro cpu start user code
D (309) light_driver: [light_init, 74]:status: 1, mode: 2
D (318) vfs: esp_vfs_register_fd_range is successful for range <54; 64) and VFS ID 1
I (328) wifi: wifi driver task: 3ffdbf84, prio:23, stack:4096, core=0

The captured output for the filtering options --print_filter="wifi esp_image:E light_driver:I" is given below:

E (31) esp_image: image at 0x30000 has invalid magic byte
I (328) wifi: wifi driver task: 3ffdbf84, prio:23, stack:4096, core=0

The options --print_filter="light_driver:D esp_image:N boot:N cpu_start:N vfs:N wifi:N *:V" show the following output:

load:0x40078000,len:13564
entry 0x40078d4c
I (569) heap_init: Initializing. RAM available for dynamic allocation:
D (309) light_driver: [light_init, 74]:status: 1, mode: 2

Configuration File

esp-idf-monitor offers option to change its default behavior with configuration file. This file can be used for example to set custom key bindings, or set a custom reset sequence for resetting the chip into bootloader mode.

For more details on the configuration file, see the IDF Monitor documentation.

Known Issues with IDF Monitor

If you encounter any issues while using IDF Monitor, check our GitHub repository for a list of known issues and their current status. If you come across a problem that hasn't been documented yet, we encourage you to create a new issue report.

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