Espressif ESP32-C6
The ESP32-C6 is an ultra-low-power and highly integrated SoC with a RISC-V core and supports 2.4 GHz Wi-Fi 6, Bluetooth 5 (LE) and the 802.15.4 protocol.
Address Space - 800 KB of internal memory address space accessed from the instruction bus - 560 KB of internal memory address space accessed from the data bus - 1016 KB of peripheral address space - 8 MB of external memory virtual address space accessed from the instruction bus - 8 MB of external memory virtual address space accessed from the data bus - 480 KB of internal DMA address space
Internal Memory - 320 KB ROM - 512 KB SRAM (16 KB can be configured as Cache) - 16 KB of SRAM in RTC
External Memory - Up to 16 MB of external flash
Peripherals - 35 peripherals
GDMA - 7 modules are capable of DMA operations.
ESP32-C6 Toolchain
A generic RISC-V toolchain can be used to build ESP32-C6 projects. It’s recommended to use the same toolchain used by NuttX CI. Please refer to the Docker container and check for the current compiler version being used. For instance:
###############################################################################
# Build image for tool required by RISCV builds
###############################################################################
FROM nuttx-toolchain-base AS nuttx-toolchain-riscv
# Download the latest RISCV GCC toolchain prebuilt by xPack
RUN mkdir riscv-none-elf-gcc && \
curl -s -L "https://github.com/xpack-dev-tools/riscv-none-elf-gcc-xpack/releases/download/v13.2.0-2/xpack-riscv-none-elf-gcc-13.2.0-2-linux-x64.tar.gz" \
| tar -C riscv-none-elf-gcc --strip-components 1 -xz
It uses the xPack’s prebuilt toolchain based on GCC 13.2.0-2.
Installing
First, create a directory to hold the toolchain:
$ mkdir -p /path/to/your/toolchain/riscv-none-elf-gcc
Download and extract toolchain:
$ curl -s -L "https://github.com/xpack-dev-tools/riscv-none-elf-gcc-xpack/releases/download/v13.2.0-2/xpack-riscv-none-elf-gcc-13.2.0-2-linux-x64.tar.gz" \
| tar -C /path/to/your/toolchain/riscv-none-elf-gcc --strip-components 1 -xz
Add the toolchain to your PATH:
$ echo "export PATH=/path/to/your/toolchain/riscv-none-elf-gcc/bin:$PATH" >> ~/.bashrc
You can edit your shell’s rc files if you don’t use bash.
Building and flashing NuttX
Installing esptool
First, make sure that esptool.py
is installed and up-to-date.
This tool is used to convert the ELF to a compatible ESP32-C6 image and to flash the image into the board.
It can be installed with: pip install esptool>=4.8.1
.
Warning
Installing esptool.py
may required a Python virtual environment on newer systems.
This will be the case if the pip install
command throws an error such as:
error: externally-managed-environment
.
If you are not familiar with virtual environments, refer to Managing esptool on virtual environment for instructions on how to install esptool.py
.
Bootloader and partitions
NuttX can boot the ESP32-C6 directly using the so-called “Simple Boot”.
An externally-built 2nd stage bootloader is not required in this case as all
functions required to boot the device are built within NuttX. Simple boot does not
require any specific configuration (it is selectable by default if no other
2nd stage bootloader is used). For compatibility among other SoCs and future options
of 2nd stage bootloaders, the commands make bootloader
and the ESPTOOL_BINDIR
option (for the make flash
) are kept (and ignored if Simple Boot is used).
If other features are required, an externally-built 2nd stage bootloader is needed.
The bootloader is built using the make bootloader
command. This command generates
the firmware in the nuttx
folder. The ESPTOOL_BINDIR
is used in the
make flash
command to specify the path to the bootloader. For compatibility
among other SoCs and future options of 2nd stage bootloaders, the commands
make bootloader
and the ESPTOOL_BINDIR
option (for the make flash
)
can be used even if no externally-built 2nd stage bootloader
is being built (they will be ignored if Simple Boot is used, for instance):
$ make bootloader
Note
It is recommended that if this is the first time you are using the board with NuttX to perform a complete SPI FLASH erase.
$ esptool.py erase_flash
Building and Flashing
This is a two-step process where the first step converts the ELF file into an ESP32-C6 compatible binary and the second step flashes it to the board. These steps are included in the build system and it is possible to build and flash the NuttX firmware simply by running:
$ make flash ESPTOOL_PORT=<port> ESPTOOL_BINDIR=./
where:
ESPTOOL_PORT
is typically/dev/ttyUSB0
or similar.ESPTOOL_BINDIR=./
is the path of the externally-built 2nd stage bootloader and the partition table (if applicable): when built using themake bootloader
, these files are placed intonuttx
folder.ESPTOOL_BAUD
is able to change the flash baud rate if desired.
Flashing NSH Example
This example shows how to build and flash the nsh
defconfig for the ESP32-C6-DevKitC-1 board:
$ cd nuttx
$ make distclean
$ ./tools/configure.sh esp32c6-devkitc:nsh
$ make -j$(nproc)
When the build is complete, the firmware can be flashed to the board using the command:
$ make -j$(nproc) flash ESPTOOL_PORT=<port> ESPTOOL_BINDIR=./
where <port>
is the serial port where the board is connected:
$ make flash ESPTOOL_PORT=/dev/ttyUSB0 ESPTOOL_BINDIR=./
CP: nuttx.hex
MKIMAGE: NuttX binary
esptool.py -c esp32c6 elf2image --ram-only-header -fs 4MB -fm dio -ff 80m -o nuttx.bin nuttx
esptool.py v4.8.1
Creating esp32c6 image...
Image has only RAM segments visible. ROM segments are hidden and SHA256 digest is not appended.
Merged 1 ELF section
Successfully created esp32c6 image.
Generated: nuttx.bin
esptool.py -c esp32c6 -p /dev/ttyUSB0 -b 921600 write_flash -fs 4MB -fm dio -ff 80m 0x0000 nuttx.bin
esptool.py v4.8.1
Serial port /dev/ttyUSB0
Connecting....
Chip is ESP32-C6 (QFN40) (revision v0.0)
[...]
Flash will be erased from 0x00000000 to 0x0003cfff...
Compressed 248628 bytes to 106757...
Wrote 248628 bytes (106757 compressed) at 0x00000000 in 2.5 seconds (effective 805.6 kbit/s)...
Hash of data verified.
Leaving...
Hard resetting via RTS pin...
Now opening the serial port with a terminal emulator should show the NuttX console:
$ picocom -b 115200 /dev/ttyUSB0
NuttShell (NSH) NuttX-12.8.0
nsh> uname -a
NuttX 12.8.0 759d37b97c-dirty Mar 5 2025 19:42:41 risc-v esp32c6-devkitc
Debugging
This section describes debugging techniques for the ESP32-C6.
Debugging with openocd
and gdb
Espressif uses a specific version of OpenOCD to support ESP32-C6: openocd-esp32.
Please check Building OpenOCD from Sources for more information on how to build OpenOCD for ESP32-C6.
You do not need an external JTAG to debug, the ESP32-C6 integrates a USB-to-JTAG adapter.
Note
One must configure the USB drivers to enable JTAG communication. Please check Configure USB Drivers for more information.
OpenOCD can then be used:
openocd -c 'set ESP_RTOS hwthread; set ESP_FLASH_SIZE 0' -f board/esp32c6-builtin.cfg
If you want to debug with an external JTAG adapter it can be connected as follows:
ESP32-C6 Pin |
JTAG Signal |
---|---|
GPIO4 |
TMS |
GPIO5 |
TDI |
GPIO6 |
TCK |
GPIO7 |
TDO |
Furthermore, an efuse needs to be burnt to be able to debug:
espefuse.py -p <port> burn_efuse DIS_USB_JTAG
Warning
Burning eFuses is an irreversible operation, so please consider the above option before starting the process.
OpenOCD can then be used:
openocd -c 'set ESP_RTOS hwtread; set ESP_FLASH_SIZE 0' -f board/esp32c6-ftdi.cfg
Once OpenOCD is running, you can use GDB to connect to it and debug your application:
riscv-none-elf-gdb -x gdbinit nuttx
whereas the content of the gdbinit
file is:
target remote :3333
set remote hardware-watchpoint-limit 2
mon reset halt
flushregs
monitor reset halt
thb nsh_main
c
Note
nuttx
is the ELF file generated by the build process. Please note that CONFIG_DEBUG_SYMBOLS
must be enabled in the menuconfig
.
Please refer to Debugging for more information about debugging techniques.
Stack Dump and Backtrace Dump
NuttX has a feature to dump the stack of a task and to dump the backtrace of it (and of all the other tasks). This feature is useful to debug the system when it is not behaving as expected, especially when it is crashing.
In order to enable this feature, the following options must be enabled in the NuttX configuration:
CONFIG_SCHED_BACKTRACE
, CONFIG_DEBUG_SYMBOLS
and, optionally, CONFIG_ALLSYMS
.
Note
The first two options enable the backtrace dump. The third option enables the backtrace dump with the associated symbols, but increases the size of the generated NuttX binary.
Espressif also provides a tool to translate the backtrace dump into a human-readable format.
This tool is called btdecode.sh
and is available at tools/espressif/btdecode.sh
of NuttX
repository.
Note
This tool is not necessary if CONFIG_ALLSYMS
is enabled. In this case, the backtrace dump
contains the function names.
Example - Crash Dump
A typical crash dump, caused by an illegal load with CONFIG_SCHED_BACKTRACE
and
CONFIG_DEBUG_SYMBOLS
enabled, is shown below:
riscv_exception: EXCEPTION: Store/AMO access fault. MCAUSE: 00000007, EPC: 420168ac, MT0
riscv_exception: PANIC!!! Exception = 00000007
_assert: Current Version: NuttX 10.4.0 2ae3246e40-dirty Sep 19 2024 14:47:41 risc-v
_assert: Assertion failed panic: at file: :0 task: backtrace process: backtrace 0x42016866
up_dump_register: EPC: 420168ac
up_dump_register: A0: 0000005a A1: 40809fc4 A2: 00000001 A3: 00000088
up_dump_register: A4: 00007fff A5: 00000001 A6: 00000000 A7: 00000000
up_dump_register: T0: 00000000 T1: 00000000 T2: ffffffff T3: 00000000
up_dump_register: T4: 00000000 T5: 00000000 T6: 00000000
up_dump_register: S0: 4080908e S1: 40809078 S2: 00000000 S3: 00000000
up_dump_register: S4: 00000000 S5: 00000000 S6: 00000000 S7: 00000000
up_dump_register: S8: 00000000 S9: 00000000 S10: 00000000 S11: 00000000
up_dump_register: SP: 4080a020 FP: 4080908e TP: 00000000 RA: 420168ac
dump_stack: User Stack:
dump_stack: base: 0x40809098
dump_stack: size: 00004040
dump_stack: sp: 0x4080a020
stack_dump: 0x4080a000: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00001880
stack_dump: 0x4080a020: 00000000 40808c90 42016866 42006e06 00000000 00000000 40809078 00000002
stack_dump: 0x4080a040: 00000000 00000000 00000000 42004d72 00000000 00000000 00000000 00000000
stack_dump: 0x4080a060: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
sched_dumpstack: backtrace| 2: 0x420168ac
dump_tasks: PID GROUP PRI POLICY TYPE NPX STATE EVENT SIGMASK STACKBASE STACKSIZE COMMAND
dump_tasks: ---- --- --- -------- ------- --- ------- ---------- ---------------- 0x40805a90 2048 irq
dump_task: 0 0 0 FIFO Kthread - Ready 0000000000000000 0x40807290 2032 Idle_Task
dump_task: 1 1 100 RR Task - Waiting Semaphore 0000000000000000 0x408081a8 1992 nsh_main
dump_task: 2 2 255 RR Task - Running 0000000000000000 0x40809098 4040 backtrace task
sched_dumpstack: backtrace| 0: 0x42008420
sched_dumpstack: backtrace| 1: 0x420089a2
sched_dumpstack: backtrace| 2: 0x420168ac
The lines starting with sched_dumpstack
show the backtrace of the tasks. By checking it, it is
possible to track the root cause of the crash. Saving this output to a file and using the btdecode.sh
:
./tools/btdecode.sh esp32c6 /tmp/backtrace.txt
Backtrace for task 2:
0x420168ac: assert_on_task at backtrace_main.c:158
(inlined by) backtrace_main at backtrace_main.c:194
Backtrace dump for all tasks:
Backtrace for task 2:
0x420168ac: assert_on_task at backtrace_main.c:158
(inlined by) backtrace_main at backtrace_main.c:194
Backtrace for task 1:
0x420089a2: sys_call2 at syscall.h:227
(inlined by) up_switch_context at riscv_switchcontext.c:95
Backtrace for task 0:
0x42008420: up_idle at esp_idle.c:74
Peripheral Support
The following list indicates the state of peripherals’ support in NuttX:
Peripheral |
Support |
NOTES |
---|---|---|
ADC |
No |
Supports internal temperature sensor |
AES |
No |
|
Bluetooth |
No |
|
CAN/TWAI |
Yes |
|
DMA |
Yes |
|
ECC |
No |
|
eFuse |
Yes |
|
GPIO |
Yes |
|
HMAC |
No |
|
I2C |
Yes |
Master and Slave mode supported |
I2S |
Yes |
|
LED/PWM |
Yes |
|
MCPWM |
Yes |
|
Pulse Counter |
Yes |
|
RMT |
Yes |
|
RNG |
Yes |
|
RSA |
No |
|
RTC |
Yes |
|
SDIO |
No |
|
SHA |
No |
|
SPI |
Yes |
|
SPIFLASH |
Yes |
|
SPIRAM |
No |
|
Temp. Sensor |
No |
|
Timers |
Yes |
|
UART |
Yes |
|
USB Serial |
Yes |
|
Watchdog |
Yes |
|
Wi-Fi |
Yes |
|
XTS |
No |
Managing esptool on virtual environment
This section describes how to install esptool
, imgtool
or any other Python packages in a
proper environment.
Normally, a Linux-based OS would already have Python 3 installed by default. Up to a few years ago,
you could simply call pip install
to install packages globally. However, this is no longer recommended
as it can lead to conflicts between packages and versions. The recommended way to install Python packages
is to use a virtual environment.
A virtual environment is a self-contained directory that contains a Python installation for a particular version of Python, plus a number of additional packages. You can create a virtual environment for each project you are working on, and install the required packages in that environment.
Two alternatives are explained below, you can select any one of those.
Using pipx (recommended)
pipx
is a tool that makes it easy to install Python packages in a virtual environment. To install
pipx
, you can run the following command (using apt as example):
$ apt install pipx
Once you have installed pipx
, you can use it to install Python packages in a virtual environment. For
example, to install the esptool
package, you can run the following command:
$ pipx install esptool
This will create a new virtual environment in the ~/.local/pipx/venvs
directory, which contains the
esptool
package. You can now use the esptool
command as normal, and so will the build system.
Make sure to run pipx ensurepath
to add the ~/.local/bin
directory to your PATH
. This will
allow you to run the esptool
command from any directory.
Using venv (alternative)
To create a virtual environment, you can use the venv
module, which is included in the Python standard
library. To create a virtual environment, you can run the following command:
$ python3 -m venv myenv
This will create a new directory called myenv
in the current directory, which contains a Python
installation and a copy of the Python standard library. To activate the virtual environment, you can run
the following command:
$ source myenv/bin/activate
This will change your shell prompt to indicate that you are now working in the virtual environment. You can
now install packages using pip
. For example, to install the esptool
package, you can run the following
command:
$ pip install esptool
This will install the esptool
package in the virtual environment. You can now use the esptool
command as
normal. When you are finished working in the virtual environment, you can deactivate it by running the following
command:
$ deactivate
This will return your shell prompt to its normal state. You can reactivate the virtual environment at any time by
running the source myenv/bin/activate
command again. You can also delete the virtual environment by deleting
the directory that contains it.