IDF Monitor

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IDF Monitor is mainly a serial terminal program which relays serial data to and from the target device’s serial port. It also provides some IDF-specific features.

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

Keyboard Shortcuts

For easy interaction with IDF Monitor, use the keyboard shortcuts given in the table.

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 line

Resets the target, into bootloader via the RTS line (if connected), so that the board runs nothing. Useful when you need to wait for another device to startup.

  • 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 run GDB project debugger to debug the application at runtime. This requires :ref: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.

IDF-specific features

Automatic Address Decoding

Whenever ESP-IDF outputs a hexadecimal code address of the form 0x4_______, IDF Monitor uses addr2line_ to look up the location in the source code and find the function name.

If an ESP-IDF app crashes and panics, a register dump and backtrace is 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

Note

Set environment variable ESP_MONITOR_DECODE to 0 or call idf_monitor.py with specific command line option: idf_monitor.py --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_monitor.py --no-reset).

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]).

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_PANIC to GDBStub on 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.

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 Verbose level.

Note

Use primary logging to disable at compilation the outputs you do not need through the logging library. Output filtering with IDF monitor is a secondary solution which 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

Known Issues with IDF Monitor

Issues Observed on Windows

  • Arrow keys, as well as some other keys, do not work in GDB due to Windows Console limitations.

  • Occasionally, when “idf.py” exits, it might stall for up to 30 seconds before IDF Monitor resumes.

  • When “gdb” is run, it might stall for a short time before it begins communicating with the GDBStub.

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