change(sdm): delete the confusing part in sdm programming guide

components/hal/esp32/include/hal/sdm_ll.h

@@ -10,12 +10,13 @@
 #include "hal/misc.h"
 #include "hal/assert.h"
 #include "soc/gpio_sd_struct.h"
+#include "soc/gpio_sd_reg.h"
 
 #ifdef __cplusplus
 extern "C" {
 #endif
 
-#define SDM_LL_PRESCALE_MAX     256
+#define SDM_LL_PRESCALE_MAX     (GPIO_SD0_PRESCALE_V + 1)
 
 /**
  * @brief Set Sigma-delta enable

components/hal/esp32c3/include/hal/sdm_ll.h

@@ -10,12 +10,13 @@
 #include "hal/misc.h"
 #include "hal/assert.h"
 #include "soc/gpio_sd_struct.h"
+#include "soc/gpio_sd_reg.h"
 
 #ifdef __cplusplus
 extern "C" {
 #endif
 
-#define SDM_LL_PRESCALE_MAX     256
+#define SDM_LL_PRESCALE_MAX     (GPIO_SD0_PRESCALE_V + 1)
 
 /**
  * @brief Set Sigma-delta enable

components/hal/esp32c5/include/hal/sdm_ll.h

@@ -10,12 +10,13 @@
 #include "hal/misc.h"
 #include "hal/assert.h"
 #include "soc/gpio_ext_struct.h"
+#include "soc/gpio_ext_reg.h"
 
 #ifdef __cplusplus
 extern "C" {
 #endif
 
-#define SDM_LL_PRESCALE_MAX     256
+#define SDM_LL_PRESCALE_MAX     (GPIO_EXT_SD0_PRESCALE_V + 1)
 
 /**
  * @brief Set Sigma-delta enable

components/hal/esp32c6/include/hal/sdm_ll.h

@@ -10,12 +10,13 @@
 #include "hal/misc.h"
 #include "hal/assert.h"
 #include "soc/gpio_ext_struct.h"
+#include "soc/gpio_ext_reg.h"
 
 #ifdef __cplusplus
 extern "C" {
 #endif
 
-#define SDM_LL_PRESCALE_MAX     256
+#define SDM_LL_PRESCALE_MAX     (GPIO_EXT_SD0_PRESCALE_V + 1)
 
 /**
  * @brief Set Sigma-delta enable

components/hal/esp32h2/include/hal/sdm_ll.h

@@ -10,12 +10,13 @@
 #include "hal/misc.h"
 #include "hal/assert.h"
 #include "soc/gpio_ext_struct.h"
+#include "soc/gpio_ext_reg.h"
 
 #ifdef __cplusplus
 extern "C" {
 #endif
 
-#define SDM_LL_PRESCALE_MAX     256
+#define SDM_LL_PRESCALE_MAX     (GPIO_EXT_SD0_PRESCALE_V + 1)
 
 /**
  * @brief Set Sigma-delta enable

components/hal/esp32p4/include/hal/sdm_ll.h

@@ -10,12 +10,13 @@
 #include "hal/misc.h"
 #include "hal/assert.h"
 #include "soc/gpio_ext_struct.h"
+#include "soc/gpio_ext_reg.h"
 
 #ifdef __cplusplus
 extern "C" {
 #endif
 
-#define SDM_LL_PRESCALE_MAX     256
+#define SDM_LL_PRESCALE_MAX     (GPIO_EXT_SD0_PRESCALE_V + 1)
 
 /**
  * @brief Set Sigma-delta enable

components/hal/esp32s2/include/hal/sdm_ll.h

@@ -10,12 +10,13 @@
 #include "hal/misc.h"
 #include "hal/assert.h"
 #include "soc/gpio_sd_struct.h"
+#include "soc/gpio_sd_reg.h"
 
 #ifdef __cplusplus
 extern "C" {
 #endif
 
-#define SDM_LL_PRESCALE_MAX     256
+#define SDM_LL_PRESCALE_MAX     (GPIO_SD0_PRESCALE_V + 1)
 
 /**
  * @brief Set Sigma-delta enable

components/hal/esp32s3/include/hal/sdm_ll.h

@@ -10,12 +10,13 @@
 #include "hal/assert.h"
 #include "hal/misc.h"
 #include "soc/gpio_sd_struct.h"
+#include "soc/gpio_sd_reg.h"
 
 #ifdef __cplusplus
 extern "C" {
 #endif
 
-#define SDM_LL_PRESCALE_MAX     256
+#define SDM_LL_PRESCALE_MAX    (GPIO_SD0_PRESCALE_V + 1)
 
 /**
  * @brief Set Sigma-delta enable

docs/en/api-reference/peripherals/sdm.rst

@@ -10,12 +10,6 @@ Introduction
 
 Delta-sigma modulation converts an analog voltage signal into a pulse frequency, or pulse density, which can be understood as pulse-density modulation (PDM) (refer to |wiki_ref|_).
 
-The main differences comparing to I2S PDM mode and DAC peripheral are:
-
-1. SDM has no clock signal, it is just like the DAC mode of PDM;
-2. SDM has no DMA, and it can not change its output density continuously. If you have to, you can update the density in a timer's callback;
-3. Based on the former two points, unlike the DAC peripheral, an external active or passive low-pass filter is required additionally to restore the analog wave (See :ref:`convert_to_analog_signal`).
-
 Typically, a Sigma-Delta modulated channel can be used in scenarios like:
 
 -  LED dimming
@@ -46,7 +40,7 @@ To install an SDM channel, you should call :cpp:func:`sdm_new_channel` to get a
 
 - :cpp:member:`sdm_config_t::gpio_num` sets the GPIO that the PDM pulses output from.
 - :cpp:member:`sdm_config_t::clk_src` selects the source clock for the SDM module. Note that, all channels should select the same clock source.
-- :cpp:member:`sdm_config_t::sample_rate_hz` sets the sample rate of the SDM module.
+- :cpp:member:`sdm_config_t::sample_rate_hz` sets the sample rate of the SDM module. A higher sample rate can help to output signals with higher SNR (Signal to Noise Ratio), and easier to restore the original signal after the filter.
 - :cpp:member:`sdm_config_t::invert_out` sets whether to invert the output signal.
 - :cpp:member:`sdm_config_t::io_loop_back` is for debugging purposes only. It enables both the GPIO's input and output ability through the GPIO matrix peripheral.
 
@@ -141,6 +135,7 @@ For example, you can take the following `Sallen-Key topology Low Pass Filter`_ a
 
     Sallen-Key Low Pass Filter
 
+(Refer to :example_file:`peripherals/sigma_delta/sdm_dac/README.md` to see the waveforms before and after filtering.)
 
 Application Examples
 --------------------

docs/zh_CN/api-reference/peripherals/sdm.rst

@@ -10,12 +10,6 @@ Sigma-Delta 调制器 (SDM)
 
 Sigma-Delta 调制器可以将模拟电压信号转换为脉冲频率或脉冲密度，该过程称为脉冲密度调制 (PDM)（请参阅 |wiki_ref|_）。
 
-与 I2S 外设中的 PDM 模式和和数模转换器 (DAC) 相比，SDM 中的 PDM 主要有以下特点：
-
-1. SDM 没有时钟信号，类似于 PDM 的 DAC 模式；
-2. SDM 没有 DMA 支持，无法持续改变其输出密度。如果需要改变 SDM 的输出密度，可以在定时器的回调函数中进行操作；
-3. 基于以上两点，不同于 DAC，要还原模拟波形，还必须使用外部的有源或无源低通滤波器，详情请参阅 :ref:`convert_to_analog_signal`。
-
 Sigma-Delta 调制通道通常应用于以下场景：
 
 -  LED 调光
@@ -46,7 +40,7 @@ Sigma-Delta 调制通道通常应用于以下场景：
 
 - :cpp:member:`sdm_config_t::gpio_num` 设置 PDM 脉冲输出的 GPIO 管脚号。
 - :cpp:member:`sdm_config_t::clk_src` 选择 SDM 模块的时钟源。注意，所有通道选择的时钟源应保持一致。
-- :cpp:member:`sdm_config_t::sample_rate_hz` 设置 SDM 模块的采样率。
+- :cpp:member:`sdm_config_t::sample_rate_hz` 设置 SDM 模块的采样率。提高采样率可以提高输出信号的信噪比，更容易在后级通过滤波获取高精度的原始信号。
 - :cpp:member:`sdm_config_t::invert_out` 设置是否反转输出信号。
 - :cpp:member:`sdm_config_t::io_loop_back` 通过 GPIO 矩阵外设，启用 GPIO 的输入和输出功能。注意，该字段仅供调试使用。
 
@@ -141,6 +135,7 @@ Kconfig 选项
 
     Sallen-Key 拓扑低通滤波器
 
+（滤波前后的波形请参阅文档 :example_file:`peripherals/sigma_delta/sdm_dac/README.md`）
 
 应用示例
 --------