11. ADC — Analog-to-Digital Converter

Goal

NUCLEO-F439ZI의 PA1 / ADC1_IN1에 입력되는 아날로그 전압을 12-bit ADC로 변환하고, 결과값을 USART3로 PC terminal에 출력한다.

Analog Voltage
0 ~ 3.3 V
     ↓
PA1
     ↓
ADC1_IN1
     ↓
12-bit ADC
     ↓
0 ~ 4095
     ↓
USART3
     ↓
PC Terminal

이번 실습의 핵심:

PA1          → Analog Mode
ADC1 Channel → Channel 1
Resolution   → 12-bit
Mode         → Continuous Conversion
Status       → EOC Polling
Result       → ADC1->DR

1. ADC 핵심

CPU는 아날로그 전압 자체를 직접 처리하지 못한다.

ADC가:

Analog Voltage
       ↓
Digital Number

로 변환한다.

STM32F439ZI ADC를 12-bit로 사용할 경우:

2^12
=
4096 levels

따라서 결과 범위:

0 ~ 4095

이다.

대략적으로:

0 V
→ ADC ≈ 0
1.65 V
→ ADC ≈ 2048
3.3 V
→ ADC ≈ 4095

로 생각할 수 있다.

2. ADC Registers

이번 코드에서 사용하는 register:

Register	역할
GPIOA->MODER	PA1을 Analog mode로 설정
RCC->APB2ENR	ADC1 clock enable
ADC1->SQR3	첫 번째 변환 channel 선택
ADC1->SQR1	Conversion sequence length
ADC1->CR2	ADC enable / continuous / conversion start
ADC1->SR	ADC status
ADC1->DR	Conversion result

주요 bit:

CR2.ADON
→ ADC Enable
CR2.CONT
→ Continuous Conversion
CR2.SWSTART
→ Software Start
SR.EOC
→ End Of Conversion

3. Board Mapping

이번 실습:

PA1
↓
ADC1_IN1

원서 F411 예제와 F439ZI에서 이 실습에 필요한 PA1 → ADC1 channel 1 mapping과 기본 register programming 방식은 그대로 사용할 수 있었다.

즉 Ch10 UART처럼 USART/pin을 크게 porting할 필요가 없었다.

4. Practice Code

Project:

Inc/
├── adc.h
├── uart.h
└── systick.h
Src/
├── adc.c
├── uart.c
├── systick.c
└── main.c

Ch10의 uart.c, Ch08의 systick.c를 그대로 재사용한다.

5. `adc.h`

#ifndef ADC_H__
#define ADC_H__
#include <stdint.h>
#include "stm32f4xx.h"
/*

Configure:



PA1



 ↓



ADC1_IN1




for analog-to-digital conversion.
*/
void pa1_adc_init(void);

/*

Start ADC1 continuous conversion.


After SWSTART is set once,
CONT mode keeps starting new conversions.
*/
void start_conversion(void);

/*

Wait until conversion is complete,
then return the ADC result.


Return range for 12-bit conversion:



0 ~ 4095



*/
uint32_t adc_read(void);
#endif

6. `adc.c`

#include "adc.h"
/*

============================================================
RCC Clock Enable Bits
============================================================
*/

/*

RCC AHB1ENR bit0:


GPIOA clock enable.


PA1 belongs to GPIOA.
*/
#define GPIOAEN         (1U << 0)

/*

RCC APB2ENR bit8:


ADC1 peripheral clock enable.
*/
#define ADC1EN          (1U << 8)

/*

============================================================
ADC Channel / Sequence Configuration
============================================================
*/

/*

ADC channel 1.


In this practice:



PA1 → ADC1_IN1




SQR3 SQ1 field selects the first channel
in the conversion sequence.


Channel number = 1.
*/
#define ADC_CH1         (1U << 0)

/*

ADC sequence length.


SQR1 L[3:0]:



0000




means one conversion in the sequence.


Therefore:



Sequence Length = 1



*/
#define ADC_SEQ_LEN_1   0x00U
/*

============================================================
ADC CR2 Bits
============================================================
*/

/*

CR2 bit0:


ADON = ADC ON


0 → ADC disabled
1 → ADC enabled
*/
#define CR2_ADON        (1U << 0)

/*

CR2 bit1:


CONT = Continuous Conversion


0 → one conversion
1 → automatically start next conversion
*/
#define CR2_CONT        (1U << 1)

/*

CR2 bit30:


SWSTART = Software Start


Setting this bit starts ADC conversion
through software.
*/
#define CR2_SWSTART     (1U << 30)

/*

============================================================
ADC Status Bit
============================================================
*/

/*

SR bit1:


EOC = End Of Conversion


Hardware sets EOC when conversion finishes
and valid data is available in DR.
*/
#define SR_EOC          (1U << 1)

/*

============================================================
PA1 + ADC1 Initialization
============================================================
*/

void pa1_adc_init(void)
{
/*
* --------------------------------------------------------
* Step 1. Enable GPIOA Clock
* --------------------------------------------------------
*
* PA1 cannot be configured until
* GPIOA receives its peripheral clock.
*/
RCC->AHB1ENR |= GPIOAEN;
/*
 * --------------------------------------------------------
 * Step 2. Configure PA1 as Analog Mode
 * --------------------------------------------------------
 *
 * GPIO MODER uses 2 bits per pin.
 *
 * PA1:
 *
 *     MODER<span>[3:2]</span>
 *
 * GPIO mode:
 *
 *     00 → Input
 *     01 → Output
 *     10 → Alternate Function
 *     11 → Analog
 *
 * Therefore both bit2 and bit3 are set.
 */
GPIOA-&gt;MODER |= (1U &lt;&lt; 2);
GPIOA-&gt;MODER |= (1U &lt;&lt; 3);


/*
 * The original practice code uses OR only.
 *
 * Result:
 *
 *     MODER<span>[3:2]</span> = 11
 *
 *     PA1 → Analog Mode
 *
 * When writing more defensive driver code,
 * clear-then-set can also be used:
 *
 * GPIOA-&gt;MODER &amp;= ~(0x3U &lt;&lt; (1 * 2));
 * GPIOA-&gt;MODER |=  (0x3U &lt;&lt; (1 * 2));
 *
 * But this Wiki keeps the original practice
 * implementation above.
 */


/*
 * --------------------------------------------------------
 * Step 3. Enable ADC1 Clock
 * --------------------------------------------------------
 *
 * ADC1 is connected to APB2.
 *
 * APB2ENR bit8:
 *
 *     ADC1EN = 1
 */
RCC-&gt;APB2ENR |= ADC1EN;


/*
 * --------------------------------------------------------
 * Step 4. Select ADC Channel
 * --------------------------------------------------------
 *
 * ADC regular sequence first conversion:
 *
 *     SQ1 = Channel 1
 *
 * PA1 is connected to ADC1_IN1.
 */
ADC1-&gt;SQR3 = ADC_CH1;


/*
 * --------------------------------------------------------
 * Step 5. Set Sequence Length
 * --------------------------------------------------------
 *
 * Only one ADC channel is converted.
 *
 * SQR1 L<span>[3:0]</span> = 0000
 *
 * This represents sequence length = 1.
 */
ADC1-&gt;SQR1 = ADC_SEQ_LEN_1;


/*
 * --------------------------------------------------------
 * Step 6. Enable ADC1
 * --------------------------------------------------------
 *
 * CR2.ADON = 1
 *
 * ADC peripheral becomes active.
 */
ADC1-&gt;CR2 |= CR2_ADON;

}
/*

============================================================
Start ADC Conversion
============================================================
*/

void start_conversion(void)
{
/*
* --------------------------------------------------------
* Step 1. Enable Continuous Conversion
* --------------------------------------------------------
*
* CONT = 1
*
* After one conversion completes,
* ADC automatically starts another conversion.
*
* Therefore SWSTART does NOT need to be issued
* every time adc_read() is called.
*/
ADC1->CR2 |= CR2_CONT;
/*
 * --------------------------------------------------------
 * Step 2. Start First Conversion
 * --------------------------------------------------------
 *
 * SWSTART = 1
 *
 * This starts the first ADC conversion.
 *
 * After that:
 *
 * CONT mode keeps conversions running.
 */
ADC1-&gt;CR2 |= CR2_SWSTART;

}
/*

============================================================
Read ADC Result
============================================================
*/

uint32_t adc_read(void)
{
/*
* --------------------------------------------------------
* Step 1. Wait for Conversion Complete
* --------------------------------------------------------
*
* ADC conversion takes a finite amount of time.
*
* EOC:
*
*     0 → conversion not complete
*     1 → conversion complete
*
* The CPU waits here until valid conversion
* data is ready.
*
* This is Polling / Busy Waiting.
/
while (!(ADC1->SR & SR_EOC))
{
/
* Wait for End Of Conversion.
*/
}
/*
 * --------------------------------------------------------
 * Step 2. Read Conversion Data
 * --------------------------------------------------------
 *
 * ADC1-&gt;DR contains the digital conversion result.
 *
 * In 12-bit mode:
 *
 *     minimum = 0
 *     maximum = 4095
 */
return ADC1-&gt;DR;

}

7. `main.c`

원본 Notion에는:

uart_print_value(sensor_value);

호출은 기록되어 있지만 uart_print_value()의 실제 함수 본문은 남아 있지 않다.

따라서 아래에서는 기존 uart_write_string()만 이용해 동일한 출력을 만들 수 있도록 Wiki용 helper를 보완했다.

#include <stdint.h>
#include "adc.h"
#include "systick.h"
#include "uart.h"
/*

============================================================
Wiki Supplement
uint32_t → Decimal ASCII Output
============================================================


The original Notion record contains:



uart_print_value(sensor_value);




but its implementation body was not archived.


This helper is added for the Wiki so the example
can be built without printf().
*/

/*

Send one unsigned integer as decimal text.


Example:



value = 1234




UART output:



1234



/
static void uart_write_uint32(uint32_t value)
{
/
* Maximum uint32_t decimal representation:
*
* 4294967295
*
* = 10 digits
*/
char buffer[10];
uint32_t i = 0;


/*
 * Special case:
 *
 * Without this check, value = 0 would
 * generate no digits because the while-loop below
 * would never execute.
 */
if (value == 0U)
{
    uart_write_string("0");
    return;
}


/*
 * Convert integer digits in reverse order.
 *
 * Example:
 *
 * value = 123
 *
 * first:
 *     123 % 10 = 3
 *
 * second:
 *     12 % 10 = 2
 *
 * third:
 *     1 % 10 = 1
 *
 * buffer initially contains:
 *
 *     '3' '2' '1'
 */
while ((value &gt; 0U) &amp;&amp; (i &lt; sizeof(buffer)))
{
    buffer<span>[i]</span> = (char)('0' + (value % 10U));

    value /= 10U;

    i++;
}


/*
 * Send the buffer backwards so the digits
 * appear in normal order.
 */
while (i &gt; 0U)
{
    char out<span>[2]</span>;

    i--;

    out<span>[0]</span> = buffer<span>[i]</span>;
    out<span>[1]</span> = '\0';

    uart_write_string(out);
}

}
/*

Print ADC value in the same logical format
recorded in the original practice:



Sensor Value: NNNN



*/
static void uart_print_value(uint32_t value)
{
uart_write_string("Sensor Value: ");
uart_write_uint32(value);

uart_write_string("\r\n");

}
int main(void)
{
/*
* Variable that stores one ADC conversion result.
*
* Expected range:
*
*     0 ~ 4095
*/
uint32_t sensor_value;
/*
 * --------------------------------------------------------
 * Step 1. Initialize USART3
 * --------------------------------------------------------
 *
 * Reuse Ch10 driver:
 *
 *     USART3
 *     PD8 TX
 *     115200 bps
 */
uart_init();


/*
 * --------------------------------------------------------
 * Step 2. Initialize ADC Input
 * --------------------------------------------------------
 *
 * PA1:
 *
 *     GPIO Analog Mode
 *     ADC1 Channel 1
 */
pa1_adc_init();


/*
 * --------------------------------------------------------
 * Step 3. Start Continuous Conversion
 * --------------------------------------------------------
 *
 * ADC:
 *
 *     CONT = 1
 *     SWSTART = 1
 *
 * ADC now repeatedly converts PA1 voltage.
 */
start_conversion();


while (1)
{
    /*
     * ----------------------------------------------------
     * Step 4. Read Latest ADC Conversion
     * ----------------------------------------------------
     *
     * adc_read():
     *
     *     Wait EOC
     *        ↓
     *     Read DR
     */
    sensor_value = adc_read();


    /*
     * ----------------------------------------------------
     * Step 5. Print ADC Value
     * ----------------------------------------------------
     *
     * Example:
     *
     *     Sensor Value: 2048
     */
    uart_print_value(sensor_value);


    /*
     * ----------------------------------------------------
     * Step 6. Slow Down Terminal Output
     * ----------------------------------------------------
     *
     * ADC itself converts continuously,
     * but there is no need to flood the PC terminal.
     *
     * Print approximately every 200 ms.
     */
    systick_msec_delay(200);
}

}

8. ADC Initialization Flow

pa1_adc_init()
│
├── GPIOA Clock Enable
│
├── PA1 → Analog Mode
│
├── ADC1 Clock Enable
│
├── SQ1 → Channel 1
│
├── Sequence Length → 1
│
└── ADON = 1

그다음:

start_conversion()
│
├── CONT = 1
└── SWSTART = 1

9. Runtime Flow

ADC continuously converting
│
▼
Analog Voltage on PA1
│
▼
ADC1_IN1
│
▼
ADC Conversion
│
▼
EOC = 1
│
▼
ADC1->DR
│
▼
sensor_value
│
▼
USART3
│
▼
PC Terminal

10. Why Analog Mode?

PA1을 ADC input으로 사용할 때:

GPIOA->MODER

를:

로 설정한다.

즉:

PA1
→ Analog Mode

이다.

GPIO digital input/output logic 대신 analog peripheral이 pin의 voltage를 사용할 수 있도록 한다.

11. Why Channel 1?

STM32 ADC는 여러 analog channel 중 어떤 것을 변환할지 선택해야 한다.

이번 연결:

PA1
ADC1_IN1
ADC Channel 1

따라서:

ADC1->SQR3 = ADC_CH1;

을 사용한다.

12. Conversion Sequence

ADC는 여러 channel을 순서대로 변환할 수도 있다.

예:

Channel 1
↓
Channel 3
↓
Channel 7
↓
...

하지만 이번 실습은 channel 하나만 사용한다.

Sequence:
SQ1
↓
Channel 1

그래서:

ADC1->SQR1 = ADC_SEQ_LEN_1;

즉:

Sequence Length = 1

로 설정한다.

13. Continuous Conversion

핵심:

ADC1->CR2 |= CR2_CONT;
ADC1->CR2 |= CR2_SWSTART;

처음:

SWSTART
↓
Conversion #1

Conversion #1이 끝나면:

CONT = 1
↓
Conversion #2
↓
Conversion #3
↓
Conversion #4
↓
...

자동으로 계속 진행된다.

따라서 main loop에서 매번:

ADC1->CR2 |= CR2_SWSTART;

할 필요가 없다.

14. EOC Polling

핵심 코드:

while (!(ADC1->SR & SR_EOC))
{
}

의미:

Conversion started
↓
EOC = 0
↓
CPU waits
↓
Conversion complete
↓
EOC = 1
↓
Read DR

Ch10 UART의:

while (!(USART3->SR & SR_TXE))

와 구조적으로 매우 비슷하다.

공통 pattern:

Check Status Flag
↓
Not Ready?
↓
Wait
↓
Ready?
↓
Access Data Register

이것이 bare-metal peripheral programming에서 매우 자주 나오는 방식이다.

15. ADC Digital Value

12-bit ADC:

0 ~ 4095

전압과 결과의 이상적인 관계는 대략:

ADC Value
≈
(VIN / VREF) × 4095

예를 들어 VREF를 3.3V로 가정하면:

VIN = 0 V
→ 0
VIN ≈ 0.825 V
→ ≈ 1024
VIN ≈ 1.65 V
→ ≈ 2048
VIN ≈ 2.475 V
→ ≈ 3071
VIN ≈ 3.3 V
→ ≈ 4095

실제 측정값은 전원, reference, noise 등에 따라 약간 달라질 수 있다.

16. Why `DR`?

변환이 끝나면 ADC hardware가 결과를:

ADC1->DR

에 저장한다.

따라서:

return ADC1->DR;

이:

Analog Input
↓
ADC Hardware
↓
Digital Result Register
↓
CPU

의 마지막 단계다.

17. Polling Limitation

현재 코드는:

while (!(ADC1->SR & SR_EOC))
{
}

로 CPU가 conversion 완료를 기다린다.

즉:

ADC Working
+
CPU Waiting

구조다.

이후에는:

ADC Interrupt
DMA

를 사용하면 CPU가 직접 매 conversion마다 기다리지 않아도 된다.

특히 Ch17 DMA에서 ADC와 연결할 수 있는 구조로 확장 가능하다.

18. Build Result

기존 실습 기록:

text = 1420 bytes
data = 0 bytes
bss  = 2560 bytes

그리고 실제 NUCLEO-F439ZI에서 build/download/run을 수행했으며, 포텐셔미터 입력 변화에 따라 UART의 ADC 값이 대략 0 ~ 4095 범위에서 변하는 것을 확인했다.

19. Verification

1. Build

make clean
make

Expected:

Build PASS
text = 1420
data = 0
bss  = 2560

2. GPIO Register

Debugger:

GPIOA->MODER

PA1 field:

MODER[3:2]
11

Expected:

PA1 = Analog Mode

3. ADC Sequence

확인:

ADC1->SQR3
ADC1->SQR1

Expected:

SQ1 = Channel 1
Sequence Length = 1

4. ADC Control

확인:

ADC1->CR2

Expected:

ADON    = 1
CONT    = 1
SWSTART = conversion started

5. ADC Result

Watch:

ADC1->DR
sensor_value

포텐셔미터를 움직일 때:

처럼 값이 변하는지 확인한다.

6. UART Terminal

Expected:

Sensor Value: 213
Sensor Value: 506
Sensor Value: 1058
Sensor Value: 2037
Sensor Value: 3120
Sensor Value: 4051

실제 값은 입력 전압에 따라 달라진다.

20. Screenshots to Add

images/ch11_build.png
images/ch11_adc_registers.png
images/ch11_adc_min.png
images/ch11_adc_mid.png
images/ch11_adc_max.png
images/ch11_terminal.png

가장 좋은 증거:

Potentiometer Position
+
ADC1->DR
+
UART Terminal Value

를 같이 보여주는 것이다.

21. Key Points

Analog Voltage
↓
PA1
↓
Analog Mode
↓
ADC1 Channel 1
↓
SWSTART
↓
Conversion
↓
EOC
↓
DR
↓
0 ~ 4095
↓
UART

PA1은 ADC1_IN1로 사용한다.
ADC input pin은 Analog mode로 설정한다.
ADC1은 APB2 clock을 사용한다.
SQR3에서 첫 번째 conversion channel을 선택한다.
SQR1에서 sequence length를 설정한다.
ADON은 ADC를 enable한다.
CONT는 continuous conversion을 enable한다.
SWSTART는 software conversion start다.
EOC는 conversion 완료를 나타낸다.
DR에는 ADC conversion 결과가 저장된다.
12-bit ADC 결과 범위는 0 ~ 4095다.
이번 구현은 EOC polling 방식이다.
실제 board에서 포텐셔미터 입력에 따른 ADC 값 변화까지 확인했다.

Chapter 11 - Hongjayeong-02/Basic_SoC_implementation GitHub Wiki

11. ADC — Analog-to-Digital Converter

Goal

1. ADC 핵심

2. ADC Registers

3. Board Mapping

4. Practice Code

5. `adc.h`

6. `adc.c`

7. `main.c`

}

8. ADC Initialization Flow

9. Runtime Flow

10. Why Analog Mode?

11. Why Channel 1?

ADC1_IN1

12. Conversion Sequence

13. Continuous Conversion

14. EOC Polling

15. ADC Digital Value

16. Why `DR`?

17. Polling Limitation

18. Build Result

19. Verification

1. Build

text = 1420 data = 0 bss = 2560

2. GPIO Register

3. ADC Sequence

4. ADC Control

5. ADC Result

6. UART Terminal

20. Screenshots to Add

21. Key Points

⚠️ GitHub.com Fallback ⚠️

Chapter 11 - Hongjayeong-02/Basic_SoC_implementation GitHub Wiki

11. ADC — Analog-to-Digital Converter

Goal

1. ADC 핵심

2. ADC Registers

3. Board Mapping

4. Practice Code

5. adc.h

6. adc.c

7. main.c

}

8. ADC Initialization Flow

9. Runtime Flow

10. Why Analog Mode?

11. Why Channel 1?

ADC1_IN1

12. Conversion Sequence

13. Continuous Conversion

14. EOC Polling

15. ADC Digital Value

16. Why DR?

17. Polling Limitation

18. Build Result

19. Verification

1. Build

text = 1420 data = 0 bss = 2560

2. GPIO Register

3. ADC Sequence

4. ADC Control

5. ADC Result

6. UART Terminal

20. Screenshots to Add

21. Key Points

⚠️ **GitHub.com Fallback** ⚠️

5. `adc.h`

6. `adc.c`

7. `main.c`

16. Why `DR`?

⚠️ GitHub.com Fallback ⚠️