18.4.8. GPTMR测量PWM
18.4.8.1. 概述
pwm_measure示例工程演示了GPTMR测量PWM波的功能。
18.4.8.2. 硬件设置
请参考具体开发板 引脚描述 部分的描述。 连接外部PWM至GPTMR输入捕获引脚。
18.4.8.3. 运行现象
运行工程，示例执行GPTMR的测量PWM波的功能，若有PWM波输入，串口终端输出如下信息，分别是PWM波的频率和占空比。
gptmr pwm measure test
[table_0]measured frequency: 1000.049987
[table_0]measured duty cycle: 50.00%
[table_1]measured frequency: 1000.049987
[table_1]measured duty cycle: 50.00%
[table_2]measured frequency: 1000.049987
[table_2]measured duty cycle: 50.00%
[table_3]measured frequency: 1000.049987
[table_3]measured duty cycle: 50.00%
[table_4]measured frequency: 1000.049987
[table_4]measured duty cycle: 50.00%
[table_5]measured frequency: 1000.049987
[table_5]measured duty cycle: 50.00%
[table_6]measured frequency: 1000.049987
[table_6]measured duty cycle: 50.00%
[table_7]measured frequency: 1000.049987
[table_7]measured duty cycle: 50.00%
[table_8]measured frequency: 1000.049987
[table_8]measured duty cycle: 50.00%
[table_9]measured frequency: 1000.059997
[table_9]measured duty cycle: 50.00%
18.4.8.4. GPTMR V2 注意事项
GPTMR V2 相比 V1 增加了 prescaler 预分频器字段，可通过宏 APP_GPTMR_TARGET_FREQ 配置目标计数器时钟频率：
#ifdef HPMSOC_HAS_HPMSDK_GPTMRV2
config.prescaler = gptmr_freq / APP_GPTMR_TARGET_FREQ;
#endif
预分频器公式：计数器时钟 = 源时钟 / prescaler
V2 的 reload/cmp 寄存器为 24-bit（最大 16,777,215），V1 为 32-bit
测量范围估算（假设源时钟 100MHz）：
APP_GPTMR_TARGET_FREQ |
prescaler |
每tick时间 |
最高可靠频率 |
最低可测频率 |
|---|---|---|---|---|
100KHz (默认) |
1000 |
10 µs |
~50KHz |
~0.006 Hz |
1MHz |
100 |
1 µs |
~500KHz |
~0.06 Hz |
10MHz |
10 |
100 ns |
~5MHz |
~0.6 Hz |
100MHz (prescaler=1) |
1 |
10 ns |
~50MHz |
~6 Hz |
Note
增大
APP_GPTMR_TARGET_FREQ可提高测量精度和可测最高频率，但会牺牲低频测量能力V2 中 prescaler 必须 ≥ 1（默认值 1），否则
gptmr_channel_config()返回status_invalid_argument