APWM Development Guide_Rev1.0

Revision History

Version	Date	Author	Reviewer	Revision Content
Rev1.0	2026-03-27	zlc		Initial document creation

1 Introduction

This document introduces the LTE-EC71X APWM (Advanced Pulse Width Modulation) interface APIs. The API interfaces are declared in the file components/kernel/lierda_api/liot_apwm/liot_apwm.h.

APWM (AON Pulse Width Modulation) generates pulses through AON pins while the module is in sleep mode. The APWM clock source is 32 kHz, supporting maximum periods from 32ms to 4096ms. A typical application scenario is driving breathing LEDs using AON pins during sleep mode.

2 API Function Overview

Function	Description
`Liot_ApwmCfg()`	Configure APWM parameters
`Liot_ApwmEnable()`	Enable or disable APWM channel

3 Type Descriptions

3.1 liot_apwm_errcode_e

APWM error codes indicate whether a function executed successfully. If execution fails, the error code indicates the failure reason. APWM reuses PWM error code definitions. For details, refer to liot_pwm_errcode_e in the PWM documentation.

3.2 Liot_ApwmIndex_e

APWM channel index enumeration, defined as follows:

Declaration

typedef enum
{
    LIOT_APWM_INDEX_0,
    LIOT_APWM_INDEX_1,
    LIOT_APWM_INDEX_2,
    LIOT_APWM_INDEX_MAX,
}Liot_ApwmIndex_e;

Parameters

LIOT_APWM_INDEX_0: APWM channel index 0
LIOT_APWM_INDEX_1: APWM channel index 1
LIOT_APWM_INDEX_2: APWM channel index 2

Description

APWM supports 3 channels, each of which can be configured and controlled independently. For pin numbers corresponding to each channel, please refer to the hardware pin multiplexing table.

3.3 Liot_ApwmPeriod_e

APWM maximum period option enumeration, defined as follows:

Declaration

typedef enum
{
    LIOT_APWM_MAX_PERIOD_4096MS = 0,
    LIOT_APWM_MAX_PERIOD_2048MS,
    LIOT_APWM_MAX_PERIOD_1024MS,
    LIOT_APWM_MAX_PERIOD_512MS,
    LIOT_APWM_MAX_PERIOD_256MS,
    LIOT_APWM_MAX_PERIOD_128MS,
    LIOT_APWM_MAX_PERIOD_64MS,
    LIOT_APWM_MAX_PERIOD_32MS,
    LIOT_APWM_MAX_PERIOD_MAX,
}Liot_ApwmPeriod_e;

Parameters

LIOT_APWM_MAX_PERIOD_4096MS: Maximum period 4096ms
LIOT_APWM_MAX_PERIOD_2048MS: Maximum period 2048ms
LIOT_APWM_MAX_PERIOD_1024MS: Maximum period 1024ms
LIOT_APWM_MAX_PERIOD_512MS: Maximum period 512ms
LIOT_APWM_MAX_PERIOD_256MS: Maximum period 256ms
LIOT_APWM_MAX_PERIOD_128MS: Maximum period 128ms
LIOT_APWM_MAX_PERIOD_64MS: Maximum period 64ms
LIOT_APWM_MAX_PERIOD_32MS: Maximum period 32ms

Description

The APWM clock source is 32 kHz. As the frequency increases, the precision of the PWM signal decreases. Selecting an appropriate period requires balancing precision and frequency requirements.

3.4 Liot_ApwmAccuracy_e

APWM accuracy option enumeration, defined as follows:

Declaration

typedef enum
{
    LIOT_APWM_ACCURACY_0 = 0,
    LIOT_APWM_ACCURACY_6 = 6,
    LIOT_APWM_ACCURACY_7 = 7,
    LIOT_APWM_ACCURACY_8 = 8,
}Liot_ApwmAccuracy_e;

Parameters

LIOT_APWM_ACCURACY_0: Accuracy not set
LIOT_APWM_ACCURACY_6: Period is Liot_ApwmPeriod_e enumeration value / 2
LIOT_APWM_ACCURACY_7: Period is selected from Liot_ApwmPeriod_e enumeration value
LIOT_APWM_ACCURACY_8: Period is Liot_ApwmPeriod_e enumeration value * 2

Description

The accuracy value affects the actual APWM period. Depending on the accuracy setting, the actual period will be adjusted based on Liot_ApwmPeriod_e, thereby achieving PWM output with different time resolutions.

3.5 Liot_ApwmCfg_t

APWM configuration parameter structure, defined as follows:

Declaration

typedef struct
{
    Liot_ApwmIndex_e idx;
    Liot_ApwmPeriod_e Period;
    Liot_ApwmAccuracy_e accuracy;
    uint16_t highPeriod;
    uint16_t lowPeriod;
}Liot_ApwmCfg_t;

Parameters

idx: APWM channel index, ranging from 0 to 2, corresponding to the Liot_ApwmIndex_e enumeration in section 4.2
Period: APWM period,取值 from the Liot_ApwmPeriod_e enumeration in section 4.3
accuracy: APWM accuracy,取值 from the Liot_ApwmAccuracy_e enumeration in section 4.4
highPeriod: High-level duration, ranging from 0 to 100
lowPeriod: Low-level duration, ranging from 0 to 100

Description

highPeriod and lowPeriod together determine the duty cycle. For example, when highPeriod is 70 and lowPeriod is 20, the duty cycle is 50% (50% high level, 50% low level).

4 API Function Details

4.1 Liot_ApwmCfg

This function is used to configure APWM parameters.

Declaration

liot_pwm_errcode_e Liot_ApwmCfg(Liot_ApwmCfg_t cfg);

Parameters

cfg: [In] APWM configuration parameter pointer, type is Liot_ApwmCfg_t as described in section 3.5.
Return Value

liot_pwm_errcode_e: Execution result code

4.2 Liot_ApwmEnable

This function is used to enable or disable the specified APWM channel.

Declaration

liot_pwm_errcode_e Liot_ApwmEnable(Liot_ApwmIndex_e idx, bool en);

Parameters

idx: [In] APWM channel index, ranging from 0 to 2, corresponding to the Liot_ApwmIndex_e enumeration in section 3.2
en: [In] Boolean value indicating whether to enable or disable the channel:
- true: Enable APWM channel
- false: Disable APWM channel

Return Value

liot_pwm_errcode_e: Execution result code
Description

This function controls the on/off state of the APWM output channel. Before calling this function, parameters should be configured first via Liot_ApwmCfg. After disabling a channel, APWM output will stop, but configuration parameters remain unchanged. Re-enabling does not require reconfiguration.

5 Code Example

Refer to the APWM-related example files for sample code.

#include <stdio.h>
#include "liot_apwm.h"
#include "liot_gpio.h"
#include "liot_os.h"

/**
* @brief APWM demo thread
*/
void apwm_demo_thread(void *argv)
{
    Liot_ApwmCfg_t apwm_cfg;
    liot_pwm_errcode_e ret;

    // Configure pin functions (modify according to actual hardware)
    liot_pin_set_func(20, 5); // Configure pin for APWM channel 0
    liot_pin_set_func(106, 5); // Configure pin for APWM channel 1
    liot_pin_set_func(25, 5); // Configure pin for APWM channel 2

    // Configure APWM channel 0 - 1 second period, 50% duty cycle
    apwm_cfg.idx = LIOT_APWM_INDEX_0;
    apwm_cfg.Period = LIOT_APWM_MAX_PERIOD_1024MS;
    apwm_cfg.accuracy = LIOT_APWM_ACCURACY_7;
    apwm_cfg.highPeriod = 50;
    apwm_cfg.lowPeriod = 50;

    ret = Liot_ApwmCfg(&apwm_cfg);
    if (ret == LIOT_PWM_SUCCESS) {
        printf("APWM 0 configuration successful\r\n");
        ret = Liot_ApwmEnable(LIOT_APWM_INDEX_0, true);
        if (ret != LIOT_PWM_SUCCESS) {
            printf("APWM 0 enable failed: %d\r\n", ret);
        }
    } else {
        printf("APWM 0 configuration failed: %d\r\n", ret);
    }

    // Configure APWM channel 1 - 500ms period, 70% duty cycle
    apwm_cfg.idx = LIOT_APWM_INDEX_1;
    apwm_cfg.Period = LIOT_APWM_MAX_PERIOD_512MS;
    apwm_cfg.accuracy = LIOT_APWM_ACCURACY_7;
    apwm_cfg.highPeriod = 70;
    apwm_cfg.lowPeriod = 30;

    ret = Liot_ApwmCfg(&apwm_cfg);
    if (ret == LIOT_PWM_SUCCESS) {
        printf("APWM 1 configuration successful\r\n");
        ret = Liot_ApwmEnable(LIOT_APWM_INDEX_1, true);
        if (ret != LIOT_PWM_SUCCESS) {
            printf("APWM 1 enable failed: %d\r\n", ret);
        }
    } else {
        printf("APWM 1 configuration failed: %d\r\n", ret);
    }

    // Configure APWM channel 2 - 100ms period, 30% duty cycle
    apwm_cfg.idx = LIOT_APWM_INDEX_2;
    apwm_cfg.Period = LIOT_APWM_MAX_PERIOD_128MS;
    apwm_cfg.accuracy = LIOT_APWM_ACCURACY_7;
    apwm_cfg.highPeriod = 30;
    apwm_cfg.lowPeriod = 70;

    ret = Liot_ApwmCfg(&apwm_cfg);
    if (ret == LIOT_PWM_SUCCESS) {
        printf("APWM 2 configuration successful\r\n");
        ret = Liot_ApwmEnable(LIOT_APWM_INDEX_2, true);
        if (ret != LIOT_PWM_SUCCESS) {
            printf("APWM 2 enable failed: %d\r\n", ret);
        }
    } else {
        printf("APWM 2 configuration failed: %d\r\n", ret);
    }

    // Disable APWM channel 0 after running for a period of time
    liot_rtos_task_sleep_ms(5000);
    ret = Liot_ApwmEnable(LIOT_APWM_INDEX_0, false);
    if (ret == LIOT_PWM_SUCCESS) {
        printf("APWM 0 disabled\r\n");
    }

    while (1)
    {
        liot_rtos_task_sleep_ms(1000);
    }
}

Execution Result:

After running the DEMO program, the module outputs three APWM signals. The figure above shows signals captured by a logic analyzer, with periods of 1s, 500ms, and 100ms respectively.

6 Precautions

The APWM clock source is fixed at 32 kHz and cannot be changed.
As the frequency increases, the precision of the PWM signal decreases. In high-frequency applications, the precision may not meet requirements.
The sum of highPeriod and lowPeriod should be less than or equal to 100, otherwise it may cause abnormal output.
Before using APWM, you need to configure the corresponding pin function to APWM output.
The APWM channel index ranges from 0 to 2, totaling 3 channels. Do not exceed this range.
Before disabling an APWM channel, ensure that the channel is enabled and running.
APWM reuses PWM error code definitions, and the error handling logic is the same as PWM.