IR Pulse Duty Cycle Detection

This sample code guide is designed to help users easily and comprehensively understand IR sample. This sample demonstrates pulse detection of high level count, low level count and frequency of a PWM with IR.

Requirements

For hardware requirements, please refer to the Requirements.

Wiring

Connect P2_1 to PWM output.

Configurations

The following macros can be configured to modify pin definitions.
- #define IR_RECV_PIN P2_1
The following macros can be configured to modify the RX threshold.
- #define IR_RX_FIFO_THR_LEVEL 2
The entry function is as follows, call this function in main() to run this sample code. For more details, please refer to the Initialization.
```
ir_pulse_detection_demo();
```

Building and Downloading

For building and downloading, please refer to the Building and Downloading.

Experimental Verification

When the pulse detection is completed, print PWM frequency, high level count, and low level count information in Debug Analyzer.

ir_pulse_detection_demo: freq xx, high_cnt xx, low_cnt xx

Code Overview

This section introduces the code and process description for initialization and corresponding function implementation in the sample.

Source Code Directory

For project directory, please refer to Source Code Directory.
Source code directory: sdk\src\sample\io_demo\ir\pulse_detection\ir_pulse_detection_demo.c.

Initialization

The initialization flow for peripherals can refer to Initialization Flow.

IR initialization flow is shown in the following figure.

../../../_images/IR_Initialization_Flow_Chart_2.png — IR RX Mode Initialization Flow Chart

Call Pad_Config() and Pinmux_Config() to initialize the pin.

static void board_ir_init(void)
{
   Pad_Config(IR_RECV_PIN, PAD_PINMUX_MODE, PAD_IS_PWRON, PAD_PULL_NONE, PAD_OUT_DISABLE, PAD_OUT_LOW);
   Pinmux_Config(IR_RECV_PIN, IRDA_RX);
}

Call RCC_PeriphClockCmd() to enable the IR clock and function.

Initialize the IR peripheral:

Define the IR_InitTypeDef type IR_InitStruct, and call IR_StructInit() to pre-fill IR_InitStruct with default values.
Modify the IR_InitStruct parameters as needed. The IR initialization parameter configuration is shown in the table below.
Call IR_Init() to initialize the IR peripheral.

IR Initialization Parameters
IR Hardware Parameters	Setting in the `IR_InitStruct`	IR
IR Clock Frequency	`IR_InitTypeDef::IR_Freq`	40000
IR Mode	`IR_InitTypeDef::IR_Mode`	`IR_MODE_RX`
IR Rx Mode	`IR_InitTypeDef::IR_RxStartMode`	`IR_RX_AUTO_MODE`
IR RX Threshold	`IR_InitTypeDef::IR_RxFIFOThrLevel`	`IR_RX_FIFO_THR_LEVEL`
Data Discard Mode	`IR_InitTypeDef::IR_RxFIFOFullCtrl`	`IR_RX_FIFO_FULL_DISCARD_NEWEST`
IR Rx Trigger Mode	`IR_InitTypeDef::IR_RxTriggerMode`	`IR_RX_DOUBLE_EDGE`
IR RX Filter Time	`IR_InitTypeDef::IR_RxFilterTime`	`IR_RX_FILTER_TIME_50ns`
IR Rx Counter Threshold Type	`IR_InitTypeDef::IR_RxCntThrType`	`IR_RX_Count_Low_Level`
IR Rx Counter Threshold	`IR_InitTypeDef::IR_RxCntThr`	2000000

Call IR_INTConfig() to enable the IR receive FIFO data count greater than the set receive threshold interrupt IR_INT_RF_LEVEL and the receive level timeout interrupt IR_INT_RX_CNT_THR.
Call IR_MaskINTConfig() to unmask the IR receive FIFO data count greater than the set receive threshold interrupt IR_INT_RF_LEVEL and the receive level timeout interrupt IR_INT_RX_CNT_THR.
Call NVIC_Init() to enable NVIC of IR.
Call IR_ClearRxFIFO() to clear IR RX FIFO.
Call IR_Cmd() to enable IR peripheral.

Functional Implementation

Interrupt Handle

IR interrupt handle flow is shown in the following figure.

When the number of data in the IR receive FIFO reaches the set receive threshold, it triggers the IR_INT_RF_LEVEL interrupt:
1. Call IR_MaskINTConfig() to mask the IR receive FIFO data count greater than the set receive threshold interrupt IR_INT_RF_LEVEL.
2. Call IR_GetRxDataLen() to get data size in RX FIFO.
3. Call IR_ReceiveBuf() to read data from RX FIFO.
4. Set rx_finish_flag to 1.
5. Call IR_ClearINTPendingBit() to clear the IR receive FIFO data count greater than the set receive threshold interrupt IR_INT_RF_LEVEL_CLR.
6. Call IR_MaskINTConfig() to unmask the IR receive FIFO data count greater than the set receive threshold interrupt IR_INT_RF_LEVEL.
7. Call IR_Cmd() to disable IR peripheral.
when the IR detects a low-level duration exceeding the set carrier cycle of IR_InitTypeDef::IR_RxCntThr, it triggers the IR_INT_RX_CNT_THR interrupt:
1. Call IR_MaskINTConfig() to mask the receive level timeout interrupt IR_INT_RX_CNT_THR.
2. Call IR_GetRxDataLen() to get data size in RX FIFO.
3. Call IR_ReceiveBuf() to read data from RX FIFO.
4. Set rx_finish_flag to 1.
5. Call IR_ClearINTPendingBit() to clear the receive level timeout interrupt IR_INT_RX_CNT_THR_CLR.
6. Call IR_MaskINTConfig() to unmask the receive level timeout interrupt IR_INT_RX_CNT_THR.
7. Call IR_Cmd() to disable IR peripheral.

High Level Count and Low Level Count and Frequency Analysis

If rx_finish_flag is set 1:
1. If bit 31 of the IR RX data IR_DataStruct[i] is set to 1, the high level count is equal to the value of the lower 31 bits of the IR RX data IR_DataStruct[i] plus 1.
2. If bit 31 of the IR RX data IR_DataStruct[i] is set to 0, the low level count is equal to the value of the IR RX data IR_DataStruct[i] plus 1.
3. The total count value total_cnt is equal to the high level count plus the low level count, if total_cnt is not equal to 0, frequency = 40000000 / total_cnt.
4. Set rx_finish_flag to 0.
5. Call IR_ClearRxFIFO() to clear IR RX FIFO.
6. Call IR_Cmd() to enable IR peripheral.