18.4.8. GPTMR measure PWM

18.4.8.1. Overview

The example shows measure PWM wave.

18.4.8.2. Board Setting

Please refer to Pin Description for specific board. Connect external PWM signal to GPTMR capture pin.

18.4.8.3. Running the example

Running the example,if there is a PWM wave input, the serial terminal outputs the following information,which are the frequency and duty cycle of the PWM wave.

gptmr pwm measure test
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 Notes

GPTMR V2 adds a prescaler field compared to V1. Configure the target counter clock via macro APP_GPTMR_TARGET_FREQ:

#ifdef HPMSOC_HAS_HPMSDK_GPTMRV2
config.prescaler = gptmr_freq / APP_GPTMR_TARGET_FREQ;
#endif

  • Prescaler formula: Counter Clock = Source Clock / prescaler

  • V2 reload/cmp registers are 24-bit (max 16,777,215), V1 is 32-bit

Measurement Range Estimation (assuming 100MHz source clock):

APP_GPTMR_TARGET_FREQ

prescaler

Tick Period

Max Reliable Freq

Min Measurable Freq

100KHz (default)

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

  • Increasing APP_GPTMR_TARGET_FREQ improves resolution and max measurable frequency, but reduces low-frequency capability

  • In V2, prescaler must be ≥ 1 (default 1), otherwise gptmr_channel_config() returns status_invalid_argument