ADC Key Detection

This sample code guide is designed to help users easily and comprehensively understand ADC sample. This sample demonstrates how to detect key presses using ADC and LPC.

Requirements

For hardware requirements, please refer to the Requirements.

Wiring

Connect P0_3 to an external key module.

The hardware connection of ADC sample code is shown in the figure below.

../../../_images/ADC_Key_Sample_Code_Hardware_Connection_Diagram.png — ADC Sample Code Hardware Connection Diagram

Configurations

The entry function is as follows, call this function in main() to run this sample code. For more details, please refer to the Initialization.
```
adc_key_demo();
```

Building and Downloading

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

Experimental Verification

Press the Reset button on the EVB board, when a key is pressed, the key information will be printed in Debug Analyzer.
```
io_demo_app_task: key mask xx, key_press 1
```
When the key is released, the key information will be printed in Debug Analyzer.
```
io_demo_app_task: key mask xx, key_press 0
```

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\adc\adc_key\adc_key_demo.c.

Initialization

Initialize the ADC peripheral:

Define the ADC_InitTypeDef type ADC_InitStruct, and call ADC_StructInit to pre-fill ADC_InitStruct with default values.
Modify the ADC_InitStruct parameters as needed. The ADC initialization parameter configuration is shown in the table below.
Call adc_mgr_register_req to request for a channel in ADC manager and initialize the ADC peripheral.

ADC Initialization Parameters
ADC Hardware Parameters	Setting in the `ADC_InitStruct` Variables	ADC
Sample Time	`ADC_InitTypeDef::adcClock`	`ADC_CLK_39K`
Bit Map	`ADC_InitTypeDef::bitmap`	0x0001
Schedule Index	`ADC_InitTypeDef::schIndex`	Index 0 is set to `EXT_SINGLE_ENDED(3)`.

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

static void board_lpc_init(void)
{
   Pad_Config(ADC_SAMPLE_PIN, PAD_PINMUX_MODE, PAD_IS_PWRON, PAD_PULL_NONE, PAD_OUT_DISABLE,
               PAD_OUT_HIGH);
   Pinmux_Config(ADC_SAMPLE_PIN, IDLE_MODE);
}

Initialize the LPC peripheral:

Define the LPC_InitTypeDef type LPC_InitStruct, and call LPC_StructInit() to pre-fill LPC_InitStruct with default values.
Modify the LPC_InitStruct parameters as needed. The LPC initialization parameter configuration is shown in the table below.
Call LPC_Init() to initialize the LPC peripheral.

LPC Initialization Parameters
LPC Hardware Parameters	Setting in the `LPC_InitStruct`	LPC
Channel	`LPC_InitTypeDef::LPC_Channel`	`ADC_SAMPLE_PIN`
Edge	`LPC_InitTypeDef::LPC_Edge`	`LPC_Vin_Below_Vth`
Threshold Voltage	`LPC_InitTypeDef::LPC_Threshold`	`LPC_3000_mV`

Call LPC_CounterReset() to reset the LPC counter.
Call LPC_WriteComparator() to set LPC comparator value.
Call LPC_INTConfig() to enable the LPC comparator interrupt LPC_INT_COUNT_COMP.
For RTL87x3D, call LPC_INTConfig() to enable interrupt signal to CPU NVIC, for RTL87x3E and RTL87x3EP, call RTC_CpuNVICEnable() to enable interrupt signal to CPU NVIC.
For RTL87x3D, call NVIC_Init to enable NVIC of LPC, for RTL87x3E and RTL87x3EP, call NVIC_Init to enable NVIC of RTC.
Call LPC_Cmd() to enable the LPC.
Call LPC_CounterCmd() to enable the LPC counter.

DLPS Mode Initialization

Call io_dlps_register() to initialize IO store/restore and do not need to worry about which IO peripheral requires specific handling.
Call io_dlps_register_enter_cb() to register callbacks to DLPS enter stage. Function io_dlps_enter_callback will be executed while entering from DLPS:
1. Call RTC_SystemWakeupConfig() to enable the LPC system wakeup function.
Call bt_power_mode_set() to set Bluetooth MAC deep sleep mode.
Call power_mode_set() to switch the system to DLPS mode.

Functional Implementation

LPC Interrupt Handle

When the LPC detects that the input voltage exceeds the set voltage threshold (LPC_3000_mV), it triggers an interrupt:

Call LPC_GetINTStatus() to check LPC_INT_COUNT_COMP interrupt status flag.
Call LPC_CounterReset() to reset the LPC counter.
Call LPC_ClearINTPendingBit() to clear the LPC comparator interrupt LPC_INT_COUNT_COMP.
Send a message to the task, and after the task receives the message:
1. Call LPC_Cmd() to disable the LPC.
2. Call LPC_CounterCmd() to disable the LPC counter.
3. Call Pad_Config() and Pinmux_Config() to initialize the pin to ADC function.
```
static void board_adc_init(void)
{
   Pad_Config(ADC_SAMPLE_PIN, PAD_SW_MODE, PAD_IS_PWRON, PAD_PULL_NONE, PAD_OUT_DISABLE, PAD_OUT_LOW);
   Pinmux_Config(ADC_SAMPLE_PIN, IDLE_MODE);
}
```
1. Call adc_mgr_enable_req to enable the specific ADC manager channel for sampling.

ADC Manager Callback Handle

When ADC sampling is completed, ADC manager callback function adc_key_read_voltage_callback will be executed.

Call adc_mgr_read_data_req() to read ADC sampling raw data of the specific ADC manager channel.
Call ADC_GetRes to get ADC conversion result, and get the key index key_index based on the conversion result.
If the key index key_index is not equal to 0xff, it means a key is pressed, and the edge of LPC is adjusted to LPC_Vin_Over_Vth to detect key release.
1. If adc_key_data.key_press[key_index] is equal to KEY_RELEASE, it means that the last state of this key was released.
  1. Set key_status_update_fg to 1.
  2. Set adc_key_data.key_press[key_index] to update the key state.
  3. Set adc_key_data.key_index to update the key index.
2. Call Pad_Config() and Pinmux_Config() to initialize the pin to LPC function.
```
static void board_lpc_init(void)
{
   Pad_Config(ADC_SAMPLE_PIN, PAD_PINMUX_MODE, PAD_IS_PWRON, PAD_PULL_NONE, PAD_OUT_DISABLE,
               PAD_OUT_HIGH);
   Pinmux_Config(ADC_SAMPLE_PIN, IDLE_MODE);
}
```
3. Call LPC_SetTriggerEdge() to set LPC trigger edge to LPC_Vin_Over_Vth.
4. Call LPC_Cmd() to enable the LPC.
5. Call LPC_CounterCmd() to enable the LPC counter.
If the key index key_index is equal to 0xff, it means a key is released, and the edge of LPC is adjusted to LPC_Vin_Below_Vth to detect key press.
1. If adc_key_data.key_index is not equal to 0xff and adc_key_data.key_press[adc_key_data.key_index] is equal to KEY_PRESS, it means that the last state of this key was pressed.
  1. Set key_status_update_fg to 1.
  2. Set adc_key_data.key_press[adc_key_data.key_index] to update the key state.
  3. Set adc_key_data.key_index to update the key index.
2. Call Pad_Config() and Pinmux_Config() to initialize the pin to LPC function.
```
static void board_lpc_init(void)
{
   Pad_Config(ADC_SAMPLE_PIN, PAD_PINMUX_MODE, PAD_IS_PWRON, PAD_PULL_NONE, PAD_OUT_DISABLE,
               PAD_OUT_HIGH);
   Pinmux_Config(ADC_SAMPLE_PIN, IDLE_MODE);
}
```
3. Call LPC_SetTriggerEdge() to set LPC trigger edge to LPC_Vin_Below_Vth.
4. Call LPC_Cmd() to enable the LPC.
5. Call LPC_CounterCmd() to enable the LPC counter.
If key_status_update_fg is set to 1, send a message to the task, and after the task receives the message, print key information.