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 the make bootloader, these files are placed into nuttx 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 -s <tcl_scripts_path> -c 'set ESP_RTOS hwthread' -f board/esp32c6-builtin.cfg -c 'init; reset halt; esp appimage_offset 0x0'

Note

  • appimage_offset should be set to 0x0 when Simple Boot is used. For MCUboot, this value should be set to CONFIG_ESPRESSIF_OTA_PRIMARY_SLOT_OFFSET value (0x10000 by default).

  • -s <tcl_scripts_path> defines the path to the OpenOCD scripts. Usually set to tcl if running openocd from its source directory. It can be omitted if openocd-esp32 were installed in the system with sudo make install.

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

Yes

Oneshot and internal temperature sensor

AES

No

Bluetooth

No

CAN/TWAI

Yes

DMA

Yes

ECC

No

eFuse

Yes

GPIO

Yes

Dedicated GPIO supported

HMAC

No

I2C

Yes

Master and Slave mode also LPI2C supported

I2S

Yes

LED/PWM

Yes

MCPWM

Yes

Pulse Counter

Yes

RMT

Yes

RNG

Yes

RSA

No

RTC

Yes

SDIO

No

SHA

Yes

SPI

Yes

SPIFLASH

Yes

SPIRAM

No

Temp. Sensor

No

Timers

Yes

UART

Yes

LPUART supported

USB Serial

Yes

Watchdog

Yes

Wi-Fi

Yes

XTS

No

Analog-to-digital converter (ADC)

One ADC unit is available for the ESP32-C6, with 7 channels.

During bringup, GPIOs for selected channels are configured automatically to be used as ADC inputs. If available, ADC calibration is automatically applied (see this page for more details). Otherwise, a simple conversion is applied based on the attenuation and resolution.

The ADC unit is accessible using the ADC character driver, which returns data for the enabled channels.

The ADC unit can be enabled in the menu System Type ‣ Peripheral Support ‣ Analog-to-digital converter (ADC).

Then, it can be customized in the menu System Type ‣ ADC Configuration, which includes operating mode, gain and channels.

Channel

ADC1 GPIO

0

0

1

1

2

2

3

3

4

4

5

5

6

6

MCUBoot and OTA Update

The ESP32-C6 supports over-the-air (OTA) updates using MCUBoot.

Read more about the MCUBoot for Espressif devices here.

Executing OTA Update

This section describes how to execute OTA update using MCUBoot.

  1. First build the default mcuboot_update_agent config. This image defaults to the primary slot and already comes with Wi-Fi settings enabled:

    ./tools/configure.sh esp32c6-devkitc:mcuboot_update_agent

  2. Build the MCUBoot bootloader:

    make bootloader

  3. Finally, build the application image:

    make

Flash the image to the board and verify it boots ok. It should show the message “This is MCUBoot Update Agent image” before NuttShell is ready.

At this point, the board should be able to connect to Wi-Fi so we can download a new binary from our network:

NuttShell (NSH) NuttX-12.4.0
This is MCUBoot Update Agent image
nsh>
nsh> wapi psk wlan0 <wifi_ssid> 3
nsh> wapi essid wlan0 <wifi_password> 1
nsh> renew wlan0

Now, keep the board as is and execute the following commands to change the MCUBoot target slot to the 2nd slot and modify the message of the day (MOTD) as a mean to verify the new image is being used.

  1. Change the MCUBoot target slot to the 2nd slot:

    kconfig-tweak -d CONFIG_ESPRESSIF_ESPTOOL_TARGET_PRIMARY
kconfig-tweak -e CONFIG_ESPRESSIF_ESPTOOL_TARGET_SECONDARY
kconfig-tweak --set-str CONFIG_NSH_MOTD_STRING "This is MCUBoot UPDATED image!"
make olddefconfig

Note

The same changes can be accomplished through menuconfig in System Type ‣ Bootloader and Image Configuration ‣ Target slot for image flashing for MCUBoot target slot and in System Type ‣ Bootloader and Image Configuration ‣ Search (motd) ‣ NSH Library ‣ Message of the Day for the MOTD.

  1. Rebuild the application image:

    make

At this point the board is already connected to Wi-Fi and has the primary image flashed. The new image configured for the 2nd slot is ready to be downloaded.

To execute OTA, create a simple HTTP server on the NuttX directory so we can access the binary remotely:

cd nuttxspace/nuttx
python3 -m http.server
 Serving HTTP on 0.0.0.0 port 8000 (http://0.0.0.0:8000/) ...

On the board, execute the update agent, setting the IP address to the one on the host machine. Wait until image is transferred and the board should reboot automatically:

nsh> mcuboot_agent http://10.42.0.1:8000/nuttx.bin
MCUboot Update Agent example
Downloading from http://10.42.0.1:8000/nuttx.bin
Firmware Update size: 1048576 bytes
Received: 512      of 1048576 bytes [0%]
Received: 1024     of 1048576 bytes [0%]
Received: 1536     of 1048576 bytes [0%]
[.....]
Received: 1048576  of 1048576 bytes [100%]
Application Image successfully downloaded!
Requested update for next boot. Restarting...

NuttShell should now show the new MOTD, meaning the new image is being used:

NuttShell (NSH) NuttX-12.4.0
This is MCUBoot UPDATED image!
nsh>

Finally, the image is loaded but not confirmed. To make sure it won’t rollback to the previous image, you must confirm with mcuboot_confirm and reboot the board. The OTA is now complete.

Flash Allocation for MCUBoot

When MCUBoot is enabled on ESP32-C6, the flash memory is organized as follows based on the default KConfig values:

Flash Layout (MCUBoot Enabled)

Region

Offset

Size

Bootloader

0x000000

64KB

E-Fuse Virtual (see Note)

0x010000

64KB

Primary Application Slot (/dev/ota0)

0x020000

1MB

Secondary Application Slot (/dev/ota1)

0x120000

1MB

Scratch Partition (/dev/otascratch)

0x220000

256KB

Storage MTD (optional)

0x260000

1MB

Available Flash

0x360000+

Remaining

Note: The E-Fuse Virtual region is optional and only used when ESPRESSIF_EFUSE_VIRTUAL_KEEP_IN_FLASH is enabled. However, this 64KB location is always allocated in the memory layout to prevent accidental erasure during board flashing operations, ensuring data preservation if virtual E-Fuses are later enabled.

Memory Map (Addresses in hex):

0x000000  ┌─────────────────────────────┐
          │                             │
          │      MCUBoot Bootloader     │
          │           (64KB)            │
          │                             │
0x010000  ├─────────────────────────────┤
          │       E-Fuse Virtual        │
          │           (64KB)            │
0x020000  ├─────────────────────────────┤
          │                             │
          │      Primary App Slot       │
          │            (1MB)            │
          │          /dev/ota0          │
          │                             │
0x120000  ├─────────────────────────────┤
          │                             │
          │     Secondary App Slot      │
          │            (1MB)            │
          │          /dev/ota1          │
          │                             │
0x220000  ├─────────────────────────────┤
          │                             │
          │      Scratch Partition      │
          │           (256KB)           │
          │       /dev/otascratch       │
          │                             │
0x260000  ├─────────────────────────────┤
          │                             │
          │    Storage MTD (optional)   │
          │            (1MB)            │
          │                             │
0x360000  ├─────────────────────────────┤
          │                             │
          │       Available Flash       │
          │         (Remaining)         │
          │                             │
          └─────────────────────────────┘

The key KConfig options that control this layout:

  • ESPRESSIF_OTA_PRIMARY_SLOT_OFFSET (default: 0x20000)

  • ESPRESSIF_OTA_SECONDARY_SLOT_OFFSET (default: 0x120000)

  • ESPRESSIF_OTA_SLOT_SIZE (default: 0x100000)

  • ESPRESSIF_OTA_SCRATCH_OFFSET (default: 0x220000)

  • ESPRESSIF_OTA_SCRATCH_SIZE (default: 0x40000)

  • ESPRESSIF_STORAGE_MTD_OFFSET (default: 0x260000 when MCUBoot enabled)

  • ESPRESSIF_STORAGE_MTD_SIZE (default: 0x100000)

For MCUBoot operation:

  • The Primary Slot contains the currently running application

  • The Secondary Slot receives OTA updates

  • The Scratch Partition is used by MCUBoot for image swapping during updates

  • MCUBoot manages image validation, confirmation, and rollback functionality

ULP LP Core Coprocessor

The ULP LP core (Low-power core) is a 32-bit RISC-V coprocessor integrated into the ESP32-C6 SoC. It is designed to run independently of the main high-performance (HP) core and is capable of executing lightweight tasks such as GPIO polling, simple peripheral control and I/O interactions.

This coprocessor benefits to offload simple tasks from HP core (e.g., GPIO polling , I2C operations, basic control logic) and frees the main CPU for higher-level processing

For more information about ULP LP Core Coprocessor check here.

Features of the ULP LP-Core

  • Processor Architecture

    • RV32I RISC-V core with IMAC extensions—Integer (I), Multiplication/Division (M), Atomic (A), and Compressed (C) instructions

    • Runs at 20 MHz

  • Memory

    • Access to 16 KB of low-power memory (LP-RAM) and LP-domain peripherals any time

    • Full access to all of the chip’s memory and peripherals when when the HP core is active

  • Debugging

    • Built-in JTAG debug module for external debugging

    • Supports LP UART for logging from the ULP itself

    • Includes a panic handler capable of dumping register state via LP UART on exceptions

  • Peripheral support

    • LP domain peripherals (LP GPIO, LP I2C, LP UART and LP Timer)

    • Full access HP domain peripherals when when the HP core is active

Loading Binary into ULP LP-Core

There are two ways to load a binary into LP-Core:

  • Using a prebuilt binary

  • Using NuttX internal build system to build your own (bare-metal) application

When using a prebuilt binary, the already compiled output for the ULP system whether built from NuttX or the ESP-IDF environment can be leveraged. However, whenever the ULP code needs to be modified, it must be rebuilt separately, and the resulting .bin file has to be integrated into NuttX. This workflow, while compatible, can become tedious.

With NuttX internal build system, the ULP binary code can be built and flashed from a single location. It is more convenient but using build system has some dependencies on example side.

Both methods requires CONFIG_ESPRESSIF_USE_LP_CORE variable to enable ULP core and it can be set using make menuconfig or kconfig-tweak commands.

Additionally, a Makefile needs to be provided to specify the ULP application name, source path of the ULP application, and either the binary (for prebuilt) or the source files (for internal build). This Makefile must include the ULP makefile after the variable set process on arch/risc-v/src/common/espressif/esp_ulp.mk integration script. For more information please refer to ulp example Makefile.

Makefile Variables for ULP Core Build:

  • ULP_APP_NAME: Sets name for the ULP application. This variable also be used as prefix (e.g. ULP application bin variable name)

  • ULP_APP_FOLDER: Specifies the directory containing the ULP application’s source codes.

  • ULP_APP_BIN: Defines the path of the prebuilt ULP binary.

  • ULP_APP_C_SRCS: Lists all C source files (.c) that need to be compiled for the ULP application.

  • ULP_APP_ASM_SRCS: Lists all assembly source files (.S or .s) to be assembled.

  • ULP_APP_INCLUDES: Specifies additional include directories for the compiler and assembler.

Here is an Makefile example when using prebuilt binary for ULP core:

ULP_APP_NAME = esp_ulp
ULP_APP_FOLDER = $(TOPDIR)$(DELIM)arch$(DELIM)$(CONFIG_ARCH)$(DELIM)src$(DELIM)$(CHIP_SERIES)
ULP_APP_BIN = $(TOPDIR)$(DELIM)Documentation$(DELIM)platforms$(DELIM)$(CONFIG_ARCH)$(DELIM)$(CONFIG_ARCH_CHIP)$(DELIM)boards$(DELIM)$(CONFIG_ARCH_BOARD)$(DELIM)ulp_riscv_blink.bin

include $(TOPDIR)$(DELIM)arch$(DELIM)$(CONFIG_ARCH)$(DELIM)src$(DELIM)common$(DELIM)espressif$(DELIM)esp_ulp.mk

Here is an example for enabling ULP and using the prebuilt test binary for ULP core:

make distclean
./tools/configure.sh esp32c6-devkitc:nsh
kconfig-tweak -e CONFIG_ESPRESSIF_USE_LP_CORE
kconfig-tweak -e CONFIG_ESPRESSIF_ULP_USE_TEST_BIN
make olddefconfig
make -j

Creating an ULP LP-Core Application

To use NuttX’s internal build system to compile the bare-metal LP binary, check the following instructions.

First, create a folder for the ULP source and header files into your NuttX example. This folder is just for ULP project and it is an independent project. Therefore, the NuttX example guide should not be followed for ULP example (folder location is irrelevant. It can be the same of the nuttx-apps repository, for instance). To include the ULP folder in the build system, don’t forget to include the ULP Makefile in the NuttX example Makefile. Lastly, configuration variables needed to enable ULP core instructions can be found above.

NuttX’s internal functions or POSIX calls are not supported.

Here is an example:

  • ULP UART Snippet:

#include <stdint.h>
#include "ulp_lp_core_print.h"
#include "ulp_lp_core_utils.h"
#include "ulp_lp_core_uart.h"
#include "ulp_lp_core_gpio.h"

#define nop() __asm__ __volatile__ ("nop")

int main (void)
{
  while(1)
  {

    lp_core_printf("Hello from the LP core!!\r\n");
    for (int i = 0; i < 10000; i++)
      {
        nop();
      }
  }

  return 0;
}

For more information about ULP Core Coprocessor examples check here. After these settings follow the same steps as for any other configuration to build NuttX. Build system checks ULP project path, adds every source and header file into project and builds it.

To sum up, here is an example. ulp_example/ulp (../ulp_example/ulp) folder selected as example to create a subfolder for ULP but folder that includes ULP source code can be anywhere. For more information about custom apps, please follow NuttX Custom Apps How-to guide, this example will demonstrate how to add ULP code into a custom application:

  • Tree view:

nuttxspace/
├── nuttx/
└── apps/
└── ulp_example/
    └── Makefile
    └── Kconfig
    └── ulp_example.c
    └── ulp/
        └── Makefile
        └── ulp_main.c

  • Contents in Makefile:

include $(APPDIR)/Make.defs

PROGNAME  = $(CONFIG_EXAMPLES_ULP_EXAMPLE_PROGNAME)
PRIORITY  = $(CONFIG_EXAMPLES_ULP_EXAMPLE_PRIORITY)
STACKSIZE = $(CONFIG_EXAMPLES_ULP_EXAMPLE_STACKSIZE)
MODULE    = $(CONFIG_EXAMPLES_ULP_EXAMPLE)

MAINSRC = ulp_example.c

include $(APPDIR)/Application.mk

include ulp/Makefile

  • Contents in Kconfig:

config EXAMPLES_ULP_EXAMPLE
  bool "ULP Example"
  default n

  • Contents in ulp_example.c:

#include <nuttx/config.h>
#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include <inttypes.h>
#include <stdint.h>
#include <stdbool.h>

#include "ulp/ulp/ulp_main.h"
/* Files that holds ULP binary header */

#include "ulp/ulp/ulp_code.h"

int main (void)
 {
   int fd;
   fd = open("/dev/ulp", O_WRONLY);
   if (fd < 0)
     {
       printf("Failed to open ULP: %d\n", errno);
       return -1;
     }
   /* ulp_example is the prefix which can be changed with ULP_APP_NAME makefile
    * variable to access ULP binary code variable */
   write(fd, ulp_example_bin, ulp_example_bin_len);
   return 0;
 }

  • Contents in ulp/Makefile:

ULP_APP_NAME = ulp_example
ULP_APP_FOLDER = $(APPDIR)$(DELIM)ulp_example$(DELIM)ulp
ULP_APP_C_SRCS = ulp_main.c

include $(TOPDIR)$(DELIM)arch$(DELIM)$(CONFIG_ARCH)$(DELIM)src$(DELIM)common$(DELIM)espressif$(DELIM)esp_ulp.mk

  • Contents in ulp_main.c:

#include <stdint.h>
#include <stdbool.h>
#include "ulp_lp_core_gpio.h"

#define GPIO_PIN 0

#define nop() __asm__ __volatile__ ("nop")

bool gpio_level_previous = true;

int main (void)
 {
    while (1)
        {
        ulp_lp_core_gpio_set_level(GPIO_PIN, gpio_level_previous);
        gpio_level_previous = !gpio_level_previous;
        for (int i = 0; i < 10000; i++)
          {
            nop();
          }
        }

    return 0;
 }

  • Command to build:

    make distclean
./tools/configure.sh esp32c6-devkitc:nsh
kconfig-tweak -e CONFIG_ESPRESSIF_GPIO_IRQ
kconfig-tweak -e CONFIG_DEV_GPIO
kconfig-tweak -e CONFIG_ESPRESSIF_USE_LP_CORE
kconfig-tweak -e CONFIG_EXAMPLES_ULP_EXAMPLE
make olddefconfig
make -j

Here is an example of a single ULP application. However, support is not limited to just one application. Multiple ULP applications are also supported. By following the same guideline, multiple ULP applications can be created and loaded using write POSIX call. Each NuttX application can build one ULP application. Therefore, to build multiple ULP applications, multiple NuttX applications are needed to create each ULP binary. This limitation only applies when using the NuttX build system to build multiple ULP applications; it does not affect the ability to load multiple ULP applications built by other means.

ULP binary can be included in NuttX application by adding #include "ulp/ulp/ulp_code.h" line. Then, the ULP binary is accessible by using the ULP application prefix (defined by the ULP_APP_NAME variable in the ULP application Makefile) with the bin keyword to access the binary data (e.g., if ULP_APP_NAME is ulp_test, the binary variable will be ulp_test_bin) and bin_len keyword to access its length (e.g., ulp_test_bin_len for ULP_APP_NAME is ulp_test).

Accessing the ULP LP-Core Program Variables

Global symbols defined in the ULP application are available to the HP core through a shared memory region. To read or write ULP variables, direct reading/writing to such memory positions are not allowed. POSIX calls are needed instead. To access the ULP variable through the HP core, consider that its name is defined by the ULP application prefix (defined by the ULP_APP_NAME variable in the ULP application Makefile) + the ULP application variable. For example if HP core tries to access a ULP application variable named result and ULP_APP_NAME in the ULP application Makefile set as ulp_app, required name for that variable will be ulp_app_result. FIONREAD or FIONWRITE ioctl calls are, then, performed with the address of a struct symtab_s previously defined with the name of the variable to be read or written.

Warning

Ensure that the related ULP application is running. Otherwise, another ULP application may interfere by using the same memory space for a different variables.

Here is a snippet for reading and writing to a ULP variable named var_test (assuming the ULP_APP_NAME is set to ulp) through the HP core:

#include <nuttx/config.h>
#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include "nuttx/symtab.h"

int main (void)
 {
   uint32_t ulp_var;
   int fd;
   struct symtab_s sym =
   {
     .sym_name = "ulp_var_test",
     .sym_value = &ulp_var,
   };
   fd = open("/dev/ulp", O_RDWR);
   ioctl(fd, FIONREAD, &sym);
   if (ulp_var != 0)
     {
       ulp_var = 0;
       ioctl(fd, FIONWRITE, &sym);
     }

   return OK;
 }

Debugging ULP LP-Core

To debug ULP LP-Core please first refer to Debugging section. Debugging ULP core consist same steps with some small differences. First of all, configuration file needs to be changed from board/esp32c6-builtin.cfg or board/esp32c6-ftdi.cfg to board/esp32c6-lpcore-builtin.cfg or board/esp32c6-lpcore-ftdi.cfg depending on preferred debug adapter.

LP core supports limited set of HW exceptions, so, for example, writing at address 0x0 will not cause a panic as it would be for the code running on HP core. This can be overcome to some extent by enabling undefined behavior sanitizer for LP core application, so ubsan can help to catch some errors. But note that it will increase code size significantly and it can happen that application won’t fit into RTC RAM. To enable ubsan for ULP please add CONFIG_ESPRESSIF_ULP_ENABLE_UBSAN in menuconfig.

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 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.

Supported Boards