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
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
First, make sure that esptool.py is installed. 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.dev4.
Configure the NuttX project: ./tools/configure.sh esp32c6-devkitc:nsh
Run make to build the project. Note that the conversion mentioned above is
included in the build process.
The esptool.py is used to flash all the binaries. However, this is also
included in the build process and we can build and flash with:
make flash ESPTOOL_PORT=<port> ESPTOOL_BINDIR=./
Where <port> is typically /dev/ttyUSB0 or similar and ./ is
the path to the folder containing the externally-built 2nd stage bootloader for
the ESP32-C6 as explained above.
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 |
|---|---|
ADC |
No |
AES |
No |
Bluetooth |
No |
CAN/TWAI |
Yes |
DMA |
Yes |
ECC |
No |
eFuse |
No |
GPIO |
Yes |
HMAC |
No |
I2C |
Yes |
I2S |
No |
Int. Temp. |
No |
LED |
No |
LED_PWM |
Yes |
MCPWM |
Yes |
Pulse Counter |
No |
RMT |
No |
RNG |
No |
RSA |
No |
RTC |
Yes |
SD/MMC |
No |
SDIO |
No |
SHA |
No |
SPI |
Yes |
SPIFLASH |
Yes |
Timers |
Yes |
UART |
Yes |
Watchdog |
Yes |
Wifi |
Yes |
XTS |
No |