sdm

[中文]

Overview

The sdm peripheral type describes an on-chip Sigma Delta Modulation output channel. BMGR generates an sdm_config_t from this configuration and calls the ESP-IDF driver/sdm.h to create the SDM channel.

BMGR is only responsible for creating and storing the SDM channel handle. After obtaining the periph_sdm_handle_t, the application can call ESP-IDF SDM APIs to enable the channel, set the pulse density, and close the channel when finished.

Supported Operating Modes

sdm does not use role or format to split modes. The configuration axis is a single SDM output channel.

Minimal Configuration

SDM Output Channel

board_peripherals.yaml:

peripherals:
  - name: sdm
    type: sdm
    config:
      gpio_num: 4
      clk_src: "SDM_CLK_SRC_DEFAULT"
      sample_rate_hz: 1000000
      invert_out: false
      io_loop_back: false

Mode Description

sdm creates one output channel. The output GPIO is specified by gpio_num. sample_rate_hz and clk_src determine the channel sampling clock configuration, and invert_out controls output polarity.

io_loop_back and allow_pd are flags that vary with the ESP-IDF version: IDF v5.x generates io_loop_back, while IDF v6.x and later generate allow_pd. When the corresponding field is configured on an unsupported ESP-IDF version, the parser ignores that field and prints a warning.

Full Field Reference

SDM Output Channel — Full Fields

- name: sdm
  type: sdm
  config:
    # GPIO pin number for SDM output (required, no default - must be >= 0)
    gpio_num: 0                     # [IO] GPIO pin number for SDM output

    # Clock source (default: SDM_CLK_SRC_DEFAULT)
    # Valid values depend on the selected chip,
    # please refer to the enum 'soc_periph_sdm_clk_src_t' in 'soc/clk_tree_defs.h'
    clk_src: "SDM_CLK_SRC_DEFAULT"

    # Sample rate in Hz (default: 1000000)
    sample_rate_hz: 1000000         # [TO_BE_CONFIRMED] Sample rate in Hz

    # Invert output signal (default: false)
    invert_out: false

    # IO loop back for debug/test (IDF < 6.0 only; ignored with a warning on IDF >= 6.0)
    io_loop_back: false

    # Allow SDM power domain to power off during sleep (IDF >= 6.0 only; ignored with a warning on IDF < 6.0)
    allow_pd: false

Field sources:

  • YAML template: esp_board_manager/peripherals/periph_sdm/periph_sdm.yml.

  • Header file: esp_board_manager/peripherals/periph_sdm/periph_sdm.h.

Applicable Devices

device type

Usage

Notes

Direct application use

Application retrieves the SDM peripheral handle via esp_board_manager_get_periph_handle

No device type in the current repository references the sdm peripheral; pulse density setting is handled by application or test code

Reference Code

  • esp_board_manager/test_apps/main/periph/test_periph_sdm.c

Board-Level Reference

  • esp_board_manager/boards/esp32_c3_lyra/board_peripherals.yaml: sdm output channel configuration.

Notes

  • gpio_num must be a non-negative GPIO number; the parser rejects values less than 0.

  • sample_rate_hz must be greater than 0.

  • invert_out, io_loop_back, and allow_pd must be boolean values.

  • Under IDF v5.x, allow_pd is not written into the generated configuration. Under IDF v6.x and later, io_loop_back is not written into the generated configuration.

  • After modifying the SDM peripheral configuration, re-run idf.py bmgr -b <board>.

Debugging Tips

API Reference

Use esp_board_manager_get_periph_handle() to retrieve the SDM peripheral handle. The handle type is periph_sdm_handle_t:

typedef struct {
    sdm_channel_handle_t  sdm_chan;  /*!< SDM channel handle */
} periph_sdm_handle_t;

sdm_chan can be passed to sdm_channel_set_pulse_density and other ESP-IDF SDM APIs to dynamically adjust the output pulse density.

Related declarations are in esp_board_manager/peripherals/periph_sdm/periph_sdm.h.

Underlying ESP-IDF driver documentation: Sigma-Delta Modulator (SDM).

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