Input Capture Example

Source code path: example/hal/pulse_in

Supported Platforms

The example can run on the following development boards:

sf32lb52-lcd_n16r8
sf32lb52-lcd_a128r16
sf32lb52-nano_a128r16
sf32lb52-nano_n16r16
sf32lb56-lcd_a128r12n1
sf32lb56-lcd_n16r12n1
sf32lb58-lcd_a128r32n1_qspi
sf32lb58-lcd_n16r32n1_qspi

Overview

Contains an example of GPT PWM input capture (Input Capture)
The example first outputs a PWM waveform through a GPT as the signal source. A jumper wire then feeds that signal into the capture timer, which measures its period, frequency, pulse width and duty cycle
PWM signal source: 52x/56x use GPTIM2_CH1, 58x uses GPTIM1_CH2
Capture timer: 52x/56x use GPTIM1_CH1, 58x uses GPTIM3_CH2/PB01 (the GPTIM2 channel pins are not routed out on the 58x development board)
Supports both interrupt acquisition (INPUT_CAPTURE_USE_IT=1, default) and polling acquisition (INPUT_CAPTURE_USE_IT=0)

Example Usage

Compilation and Programming

Switch to the example project directory and run the scons command to compile (<board> is the board name):

scons --board=sf32lb52-lcd_n16r8 -j8

build_sf32lb52-lcd_n16r8_hcpu\uart_download.bat, select the port as prompted to download:

build_sf32lb52-lcd_n16r8_hcpu\uart_download.bat

Uart Download

please input the serial port num:5

For detailed steps on compilation and downloading, please refer to the Quick Start Guide.

Configure the Project

The example needs no extra configuration; the default configuration is enough to build and run it. To inspect the project options, run:

sdk.py menuconfig --board=sf32lb52-lcd_n16r8

Hardware Connection

After the example starts, it first outputs a PWM waveform as the signal source (default 200Hz, 20% duty cycle) and keeps it running. Short the PWM output pin to the input capture pin with a jumper wire to start measuring.

PWM output and capture pins are listed below:

Board Name	PWM Output	PWM Output Pin	Capture Timer	Capture Pin
sf32lb52-nano	GPTIM2_CH1	PA09	GPTIM1_CH1	PA27
sf32lb52-lcd	GPTIM2_CH1	PA09	GPTIM1_CH1	PA27
sf32lb56-lcd	GPTIM2_CH1	PA36	GPTIM1_CH1	PA27
sf32lb58-lcd	GPTIM1_CH2	PA51	GPTIM3_CH2	PB01

Note:

58x uses GPTIM3_CH2 (PB01) in the LPSYS domain
The 4th parameter of HAL_PIN_Set(pad, func, flags, hcpu) is documented as the hcpu/lcpu selection, but in practice it is derived from pad: HPSYS pins (PA, pad < PIN_PAD_MAX_H) are forced to hcpu and LPSYS pins (PB, pad >= PIN_PAD_MAX_H) are forced to lcpu, so the value 0/1 passed in is ignored
Handling of the duplicate interrupt entry: the example drives the GPT through the HAL and does not use the hwtimer device, so the root proj.conf disables the hwtimer driver (# CONFIG_BSP_USING_TIM is not set). With that driver off, drv_pwm_tim.c takes over the GPTIMx_IRQHandler names (they are guarded by !BSP_USING_TIM), so the PWM instances that correspond to the capture timers have to be disabled as well: PWMT1 maps to GPTIM1 and PWMT3 maps to GPTIM3, while this example captures on GPTIM1 (52x/56x) and GPTIM3 (58x). The root proj.conf therefore turns PWMT1 off (the 52x boards enable it by default, other chips leave it off, so it is a no-op for them); PWMT3 only matters on 58x and is turned off in sf32lb58x/proj.conf (the 56x boards do enable PWMT3, but they capture on GPTIM1 and are unaffected). If you need the hwtimer device together with this example, use another timer for input capture

Example Output Results Display

Log output (interrupt mode, INPUT_CAPTURE_USE_IT=1, default):

SFBL
Start PWM signal source!
GPT_clock 24000000,psc 2, Period 60000,Pulse 12000
PWM signal source setup done!
Start input capture demo (interrupt mode)!
connect PWM output pin to capture input pin with a jumper wire
captured(IT): period=5000 us, freq=200 Hz, pulse=1000 us, duty=20%
captured(IT): period=5000 us, freq=200 Hz, pulse=1000 us, duty=20%

Log output (polling mode, INPUT_CAPTURE_USE_IT=0):

SFBL
Start PWM signal source!
GPT_clock 24000000,psc 2, Period 60000,Pulse 12000
PWM signal source setup done!
Start input capture demo!
connect PWM output pin to capture input pin with a jumper wire
captured: period=5000 us, freq=200 Hz, pulse=1000 us, duty=20%
captured: period=5000 us, freq=200 Hz, pulse=1000 us, duty=20%

The capture result is printed once per second: the signal source is a 200Hz/20% duty cycle PWM, corresponding to a period of 5000us and a pulse width of 1000us
If the jumper wire is not connected properly, it prints once per second:

no capture event, check the jumper wire!

Capture Principle

PWM input capture mode: the period channel (rising edge, direct TIx capture) stores the period value, and the pulse channel (falling edge, indirect TIx capture, same pin as the period channel) stores the pulse width value
Slave mode reset: the counter is cleared on the period edge, so CCR directly holds the period/pulse value of the current cycle, no need to compute the difference between two adjacent captures
52x/56x use TI1FP1 to trigger the slave mode reset (GPTIM1_CH1), 58x uses TI2FP2 (GPTIM3_CH2)
The capture counter clock is PCLK1/(CAPTURE_PRESCALER+1) (currently CAPTURE_PRESCALER=9, i.e. divide by 10). The CCR is 16-bit, so the maximum measurable period is about 65535/(PCLK1/(CAPTURE_PRESCALER+1)); if a higher PCLK1 on the target chip overflows this range on long periods, increase the prescaler.
Capture timer selection (macro definitions in main.c):

#if defined(SF32LB52X) || defined(SF32LB56X)

#define CAPTURE_INSTANCE     hwp_gptim1
#define CAPTURE_CORE         CORE_ID_HCPU
#define CAPTURE_TRIGGER      GPT_TS_TI1FP1
#define CAPTURE_PERIOD_CH    GPT_CHANNEL_1
#define CAPTURE_PULSE_CH     GPT_CHANNEL_2
#define CAPTURE_PERIOD_FLAG  GPT_FLAG_CC1
#define CAPTURE_PULSE_FLAG   GPT_FLAG_CC2
#define CAPTURE_PERIOD_ACT   HAL_GPT_ACTIVE_CHANNEL_1
#define CAPTURE_PULSE_ACT    HAL_GPT_ACTIVE_CHANNEL_2
#define CAPTURE_IRQn         GPTIM1_IRQn
#define CAPTURE_IRQ_HANDLER  GPTIM1_IRQHandler

#elif defined(SF32LB58X)

#define CAPTURE_INSTANCE     hwp_gptim3
#define CAPTURE_CORE         CORE_ID_LCPU
#define CAPTURE_TRIGGER      GPT_TS_TI2FP2
#define CAPTURE_PERIOD_CH    GPT_CHANNEL_2
#define CAPTURE_PULSE_CH     GPT_CHANNEL_1
#define CAPTURE_PERIOD_FLAG  GPT_FLAG_CC2
#define CAPTURE_PULSE_FLAG   GPT_FLAG_CC1
#define CAPTURE_PERIOD_ACT   HAL_GPT_ACTIVE_CHANNEL_2
#define CAPTURE_PULSE_ACT    HAL_GPT_ACTIVE_CHANNEL_1
#define CAPTURE_IRQn         GPTIM3_IRQn
#define CAPTURE_IRQ_HANDLER  GPTIM3_IRQHandler

#endif

Capture pin configuration (capture_pin_set in main.c):

#if defined(SF32LB52X) || defined(SF32LB56X)
    HAL_PIN_Set(PAD_PA27, GPTIM1_CH1, PIN_NOPULL, 1);
#elif defined(SF32LB58X)
    HAL_PIN_Set(PAD_PB01, GPTIM3_CH2, PIN_NOPULL, 0);
#endif

Switching between Polling and Interrupt Modes

Switch the acquisition mode with the INPUT_CAPTURE_USE_IT macro (at the top of main.c):

1 (default): interrupt mode, HAL_GPT_IC_CaptureCallback collects data in the interrupt, the main loop waits on a semaphore, and the log output format is captured(IT): ...
0: polling mode, the main loop polls the capture flag register

Note: interrupt mode requires the example to define the interrupt entry of the capture timer (CAPTURE_IRQ_HANDLER). If the project also enables another driver that claims the same timer (such as a hwtimer instance), the interrupt entry names collide, see the notes under Supported Platforms.

Exception Diagnosis

If the expected logs and waveform output do not appear, troubleshooting can be performed from the following aspects:

Whether the hardware connection is normal (whether the jumper wire correctly shorts the PWM output pin to the capture pin)
Whether pin configuration is correct
Whether the pin corresponds to the correct channel
No capture data: confirm the PWM signal source is outputting normally and the jumper wire connection is firm

For any technical queries, please open an issue on GitHub.

Reference Documents

Update Log

Version	Date	Release Notes
0.0.1	9/2026	Initial version (converted from example/hal/pwm to an input capture example)