18.4.3. GPTMR input captrue

18.4.3.1. Overview

The example shows input capture.

18.4.3.2. Board Setting

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

18.4.3.3. Running the example

Running the example, the serial terminal outputs the following information,and prints out the edge interval time captured each time,that is, the time of one cycle.

gptmr input capture test
capture the pulse width : 100001 tick
capture the pulse width : 100000 tick
capture the pulse width : 100001 tick
capture the pulse width : 100001 tick
capture the pulse width : 100001 tick
capture the pulse width : 100001 tick
capture the pulse width : 100001 tick
capture the pulse width : 100001 tick
capture the pulse width : 100000 tick
capture the pulse width : 100000 tick
capture the pulse width : 100001 tick
capture the pulse width : 100001 tick
capture the pulse width : 100001 tick
capture the pulse width : 100001 tick
capture the pulse width : 100001 tick
capture the pulse width : 100001 tick
capture the pulse width : 100000 tick
capture the pulse width : 100001 tick
capture the pulse width : 100001 tick

18.4.3.4. 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