Pin Capture Timer library for RP2040

A library for capturing signal edges on RP2040 pins using PIO and DMA. It is compatible with both the Pico SDK and Arduino.

How to use

• With Pico SDK Add capture_edge.pio, capture_edge.h, and capture_edge.c to your project.
  Update CMakeLists.txt to include pico_generate_pio_header and the required libraries: pico_stdlib, hardware_irq, hardware_pio, hardware_clocks, and hardware_dma.
  See CMakeLists.txt.

• With Arduino Add capture_edge.pio.h, capture_edge.h, and capture_edge.c to your project.

• Set the number of pins to capture with CAPTURE_EDGE_PIN_COUNT in capture_edge.pio, or in capture_edge.pio.h when using Arduino.

• Captured pins start at pin_base. Any consecutive GPIOs starting from that pin can be captured.

• Define capture handlers that receive the counter value and the edge type (rising or falling).

• Change CAPTURE_EDGE_IRQ_NUM if it conflicts with interrupts used by other PIO state machines. Valid values are 0 to 3.

See main.c for an example that calculates frequency and duty cycle.

The counter increments every 5 clock cycles. This value is defined in COUNTER_CYCLES.

To obtain the total clock divisor, multiply:

COUNTER_CYCLES * clk_div

Functions

void capture_edge_init(PIO pio, uint pin_base, uint pin_count, float clk_div, uint irq)

Parameters:

• pio — load the capture program into pio0 or pio1
• pin_base — first GPIO to capture
• pin_count — number of consecutive GPIOs to capture (1 or 2; passing 0 or a value greater than 2 triggers panic())
• clk_div — PIO clock divisor
• irq — PIO IRQ to use. Valid values for pio0: PIO0_IRQ_0, PIO0_IRQ_1; for pio1: PIO1_IRQ_0, PIO1_IRQ_1. This is useful when other state machines are also using IRQs.

Returns:

• State machine used

void capture_edge_set_handler(uint pin, capture_handler_t handler)

Parameters:

• pin — pin to capture
• handler — callback function called when an edge is captured

void capture_edge_remove(void)

Clears the handlers and removes the PIO program from memory.

Handler function

void capture_handler(uint counter, edge_type_t edge)

Parameters received:

• counter — captured counter value
• edge — edge type: EDGE_RISING = 2, EDGE_FALLING = 1

Accuracy

With clk_div = 1, the frequency measurement resolution is 18 clock cycles (9 cycles per edge).
At a 125 MHz system clock, this gives:

• edge timing resolution: 0.072 µs
• frequency measurement resolution: 0.144 µs

Capturing edges with the RP2040 and verifying the signal with an oscilloscope

An Arduino Uno generates the signal, a Mega is used as the oscilloscope, and the RP2040 captures the edges