Microcontrollers: Lecture 6 Sensors, ADC,...

1

Microcontrollers: Lecture 6 Sensors, ADC, DMA

Michele Magno

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Calendar

07.04.2016: Power consumption; Low power States; Buses, Memory, GPIOs

08.04.2016 Interrupts, Timers, Exercises

15.04.2016 Serial Communications

21.04.2016 – 22.04.2016 Programming STM32

28.04.2016 ADC, DMA

29.04.2016 Sensors / Radios

Projects presentation and exercises.

3

CORTEXTM-M3CPU

24 MHz

AR

M®

Pe

rip

he

ral B

us

(ma

x 2

4M

Hz)

2 x I2C

1 x SPI

2 x USART/LINSmartcard / IrDa

Modem Control

37/51/80 I/Os

Up to 16 Ext. ITs

JTAG/SW Debug

Power SupplyReg 1.8V

POR/PDR/PVD

DMA

7 Channels

Nested vect IT Ctrl

1 x USART/LINSmartcard/IrDa

Modem Control

1 x SPI

Bridge

Bridge

1 x Systick Timer

AR

M®

Lit

e H

i-S

pee

d B

us

Ma

trix

/ A

rbit

er

(ma

x 2

4M

Hz)

RTC / AWU

ARM® Peripheral Bus

(max 24MHz)

XTAL oscillators32KHz + 4~25MHz

Int. RC

oscillators40KHz + 8MHz

PLL

8kB SRAM

Fla

sh

I/F

64kB - 128kB Flash Memory

Clock Control

20B Backup Data

1 x 12-bit ADC

up to16 channels

Temperature Sensor

2 x Watchdog(independent & window)

6 x 16-bit Timer1 x CEC

2-channel 12-bit DAC

1 x 16-bit PWM Synchronized AC Timer

• Core and operating conditions

- ARM® Cortex™-M3

- 1.25 DMIPS/MHz up to 24 MHz

- 2.0 V to 3.6 V range

- -40 to +105 °C

• LQFP48, LQFP/BGA64, LQFP100

• Advanced analog- 12-bit1.2 µs conversion time ADC

- Dual channel 12-bit DAC

• Enhanced control- 16-bit motor control timer

- 6x 16-bit PWM timers

• Rich connectivity- 8 communications peripherals

STM32 Value line 64K-128KBytes System Diagram

4

Sensors

4

Integrated 9DoF IMU (Invensense)

Low-power cameras (Centeye, Awaiba, SoftKinetic)

IR sensors (LEAP, PMD)

EF sensors (Microchip GestIC, Plessy sensors)

ECG contactless (EPIC from Plessey) and bio sensors

Multi-Gas sensors

Contactless Voltage + Current

Acoustic sensors (MEMS, Analog, Digital)

Grove Starter Kit for LaunchPad

5

Sensors data acquisition

Data acquisition system components:

Sensors:

Convert analogue measurements of physical quantities (e.g. temperature, pressure, humidity, velocity, flow-rate, linear

motion, position) into electrical signals (voltage or current).

6

Data acquisition system components

Signal conditioning (filtering and amplification):- The operations required to convert the measured analogue signal to the

electrical signal range of the analogue-to-digital converter (ADC) may involve filtering, amplification, attenuation or impedance transformation.

Analogue-to-Digital Converter (ADC):- Input: Signal to be measured;

- Output: A digital code compatible with the digital processing system;

- Requires:

• Sample-and-hold: Used to take a snapshot of the continuously changinginput signal and maintain the value over the sample interval set by a clocksystem;

• A sampling frequency based on the Nyquist theorem.

7

ADC conversion Sample and Hold

Sample and Hold circuit does the signal time quantization

Restriction to digital information processing.

Known digital computers can only process discrete time series

Sample and hold-devices.

Ideally: width of clock pulse 0

Convert signal function in a series of value

8

Analogue-to-Digital Converter (ADC)

The ADC takes the voltage from the acquisition system (after signal conditioning) and converts it to an equivalent digital code;

ADC architectures: Successive Approximation (SAR)

Sigma Delta (SD or )

Slope or Dual Slope

Pipeline

Flash

ADC ideal transfer function

ADC performance

9

ADC performance

Resolution, R:

The resolution specifies the width of the digital output word;

- 10, 12, 16 Bit ADC

The width of the word implies the smallest change to the analogue voltage that

can be converted into a digital code;

The Least Significant Bit (LSB):

Accuracy:

Degree of conformity of a digital code representing the analogue

voltage to

Speed:

Maximum output data rate expressed in sample per second (sps)

n

ref

LSB

VV

2

10

ADC Block Examples

Voltage reference

Clock sources

Conversion trigger

11

ADC Features

3 ADCs : ADC1 (master), ADC2 and ADC3 (slaves)

Maximum frequency of the ADC analog clock is 36MHz.

12-bits, 10-bits, 8-bits or 6-bits configurable resolution.

ADC conversion rate with 12 bit resolution is up to:

2.4 M.sample/s in single ADC mode,

4.5 M.sample/s in dual interleaved ADC mode,

7.2 M.sample/s in triple interleaved ADC mode.

Conversion range: 0 to 3.6 V.

ADC supply requirement: VDDA = 2.4V to 3.6V at full speed and down to 1.65V

at lower speed.

Up to 24 external channels.

3 ADC1 internal channels connected to:

Temperature sensor,

Internal voltage reference : VREFINT (1.2V typ),

VBAT for internal battery monitoring.

12

ADC – Summary and examples

• The 12-bit ADC is a successive approximation analog-to-digital converter. It has up to 18 multiplexed channels allowing it

measure signals from 16 external and two internal sources.

• A/D conversion of the various channels can be performed in single, continuous, scan or discontinuous mode. The result of

the ADC is stored in a left-aligned or right-aligned 16-bit data register.

• The analog watchdog feature allows the application to detect if the input voltage goes outside the user-defined high or low

thresholds.

• The ADC input clock is generated from the PCLK2 clock divided by a prescaler.

13

12-bit successive approximation ADC

ADC

14

Tconv = n * TCK

Successive Approximation ADC

15

Analog references / supply

ADC

16

The ADCCLK clock provided by the

Clock Controller is synchronous with

the PCLK2 (APB2 clock). The RCC

controller has a dedicated

programmable prescaler for the ADC

clock

If prescaler == 0 on the STM32

discovery ADCCLK==36MHz

ADC

17

RCC – Real Time Clock Control

18

There are 16 multiplexed channels. It is

possible to organize the conversions in

two groups: regular and injected. A group

consists of a sequence of conversions

which can be done on any channel and in

any order.

The Temperature sensor is connected to

channel ADCx_IN16 and the internal

reference voltage VREFINT is connected

to ADCx_IN17. These two internal

channels can be selected and converted

as injected or regular channels.

The recommended sampling time for the

temperature sensor is 17.1 μs.

ADC

19

Conversion can be triggered by an external

event (e.g. timer capture, EXTI line)

ADC

20

Since converted regular channels value are

stored in a unique data register, it is

necessary to use DMA for conversion of

more than one regular channel.

Only the end of conversion of a regular

channel generates a DMA request, which

allows the transfer of its converted data

from the ADC_DR register to the destination

location selected by the user.

ADC

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When the conversion is done, data is

stored in 16 bits registers and the proper

flags are set to indicate the end of

conversion

ADC

22

ADC speed performances

AHB_PRESC

/1,2,..512

APB2_PRESC

/1, 2, 4, 8,16

ADC_PRESC

/2,4, 6, 8

ADC_CLK

(36MHz max)

AHBCLK

(168MHz max)

(1). ADC_PRESC = /2

(2). ADC_PRESC = /4

(a)APB_PRESC = /2

(b)APB_PRESC = /1

SYSCLK

(168MHz max)

APB2CLK

(84MHz max)

AHBCLK APB2CLK ADC_CLK ADC speed(15 cycles)

168MHz (a)84MHz

(2)21MHz

0.714μs1.4 Msample/s

144MHz (a)72MHz

(1)36MHz


120MHz (a)60MHz

(1)30MHz

0.5μs2 Msample/s

96MHz (a)48MHz

(1)24MHz


72MHz (b)72MHz

(1)36MHz


23

ADCCLK, up to 36MHz, taken from PCLK through a prescaler (Div2, Div4, Div6 and Div8).

Programmable sample time for each channel (from 4 to 480 clock cycles)

Total conversion Time = TSampling + Tconversion

ADCx

112 cycles

144 cycles

480 cycles

SMPx[2:0]

With Sample time= 3 cycles @ ADC_CLK = 36MHz total conversion time is equal

to:

ADC ConversionTime

ADCCLKPrescaler

/2, /4, /6 or /8PCLK

3 cycles

15 cycles

28 cycles

84 cycles

58 cycles

Sa

mp

leT

ime

Se

lec

tion

Resolution TConversion

12 bits 12 Cycles

10 bits 10 Cycles

8 bits 8 Cycles

6 bits 6 Cycles

resolution Total conversion Time

12 bits 12 + 3 = 15cycles 0.416 us 2.4 Msps

10 bits 10 + 3 = 13 cycles 0.361 us 2.71 Msps

8 bits 8 + 3 = 11 cycles 0.305 us 3.27 Msps

6 bits 6 + 3 = 9 cycles 0.25 us 4 Msps

24

Analog peripherals in STM33: Comparators

No CPU active if not needed

ADC

Comparators

25

Comparator 1 features 25

• Non-inverting input selectable from 24 I/Os

• Selectable edge detection through EXTI Line 21

• COMP1 and ADC can’t be used at same time since they share the ADC switch matrix

VSS

CH25

CH24

CH23

CH4

ADC

VCOMP

VREFINT

1.22V

VDD

10K400K

10K400K

+

-

COMP1

CH5

CH22

Temp. Sensor *

VREFINT *

Group 8

Group 1

Group 9

Group 7

Group 3

Group 2

CH10

CH11

CH12

CH13

CH1

CH2

CH3

CH0

CH14

CH15

CH19

CH20

CH21

CH9

CH8

CH6

CH7

CH18

ADC Switch matrix

EXTI 21

CMP1OUT

Routing Interface

PC0

PC1

PC2

PC3

PA0

PA1

PA2

PA3

PA6

PA7

PC4

PC5

PB12

PB13

PB14

PB15

PB0

PB1

PA4

PA5

PE7

PE8

PE9

PE10

26

Comparator 2 features 1/2 26

• Rail-to-rail comparator with selectable threshold: Internal reference voltage VREFINT, VREFINT submultiples (1/4, 1/2, 3/4), DAC output 1 & 2 or one external I/0 (PB3).

• Selectable non-inverting input from external I/Os: PB4 or PB5.

• Selectable edge detection through EXTI line 22.

Group 6GR 6-1

GR 6-2

PB3

TIM3 OCREF Clear

TIM3 Input Capture 4

TIM2 OCREF Clear

TIM2 Input Capture 4

TIM4 Input Capture 4TIM4 OCREF ClearTIM10 Input Capture 1

DAC_OUT1

VREFINT (1.22V)

-

+

¾ VREFINT

½ VREFINT

¼ VREFINT

PB4

PB5 EXTI 22

COMP2

DAC_OUT2

VREFINT

CMP2OUT

26

27

Comparator 2 features 2/2 27

Group 6GR 6-1

GR 6-2

PB3

DAC_OUT1

VREFINT (1.22V)

-

+

¾ VREFINT

½ VREFINT

¼ VREFINT

PB4

PB5 EXTI 22

COMP2

DAC_OUT2

VREFINT

CMP2OUT

27

• COMP2 output can be redirected to:

• Timer input captures for pulse width or signal frequency measurements

• Timer output compare reference clear signal “OCREFCLR”, putting the PWM signal in safe state as soon as analog input voltage crosses the reference.

TIM2 IC4

TIM2 OCRECLR

TIM3 IC4

TIM3 OCREFCLR

TIM4 IC4

TIM4 OCRECLR

TIM10 IC1

OUTSEL[2:0]

28

Comparators in Window mode 1/2 28

• Interrupt and Wake-up

modes:

• Vin > Upper threshold

• Vin < Lower threshold

• Lower threshold < Vin < Upper threshold

• Vin < Lower threshold or Vin > Upper threshold

Lower threshold:

Multiple source

+

-

-

+

Upper threshold:

VREFINT = 1.22V

Window comparator

configuration switch

Input voltage

COMP2

COMP1

PB4

PB5

GR 6-1

GR 6-2

30

Digital Sensors are Analog?

MCU

I2C

Analog (thermistor)

Neel to be calibrated

Resolution is affected by reference resistance precision

Conditioning circuit has to be accurately designed

Use of microcontroller ADC

Low cost

Digital (IC temperature)

Factory calibrated

Fixed resolution and high accuracy

Expensive

31

Direct Memory Access - DMA

32

DMA Characteristics

Direct memory access (DMA) is used to provide high-speed data transfer between peripherals and

memory as well as memory to memory.

Data can be quickly moved by DMA without any CPU actions.

It keeps CPU resources free for other operations.

DATA TRANSFERS:

• With CPU:

• ldr

• str

• …

• ldr

• Str

• With DMA:

• Give the start command

• Wait the interrupt when transfer is completed

33

DMA in STM32F4

The two DMA controllers have 16 streams in total (8 for DMA1 and 8 for DMA2), each stream has

8 different channels each dedicated to managing memory access requests from one

peripheral. It has an arbiter for handling the priority between DMA requests.

• 16 streams for dedicated hardware DMA requests,

software trigger is also supported. The

configuration is done by software.

• 4 priority levels (very high, high, medium, low) or

hardware in case of equality (request 1 has priority

over request 2, etc.)

• Independent source and destination transfer size

(byte, half word, word), Source/destination

addresses must be aligned on the data size.

• 5 event flags (DMA Half Transfer, DMA Transfer

complete, DMA Transfer Error, DMA FIFO Error,

Direct Mode Error) logically ORed together in a

single interrupt request for each stream

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DMA transfer modes: memory-to-memory, peripheral-to-memory, memory-to-

peripheral.

• Memory-to-Memory:

- Transfer data from one memory buffer to another

- Circular and Direct modes are not allowed.

- Only the DMA2 controller is able to perform memory-to-memory transfers

DMA Memory to memory

35

DMA Memory and peripherals

• Memory-to-Peripheral or Peripheral-to-Memory:

- When the threshold level of the FIFO is reached, its content is drained and stored into the

destination.

- Direct Mode: the threshold level of the FIFO is not used. After each single data transfer from

the peripheral to the FIFO, the data is immediately drained and stored into the destination.

Memory-to-Peripheral Peripheral-to-Memory

36

DMA Block scheme

After an event, the peripheral

sends a request signal to the DMA

Controller.

8 channels are multiplexed In one

stream.

The DMA controller serves the

request depending on the streams

priorities.

The DMA channels can also work

without being triggered by a request

from a peripheral. This mode is

called Memory to Memory mode.

37

DMA Block scheme

• DMA requests are collected and

channel multiplexed.

• The arbiter manages the stream

requests based on their priority and

launches the peripheral/memory

access sequences.

• The priorities are managed in two

stages:

- Software (defined priority)

- Hardware (if 2 requests have

the same software priority

level, the channel with the

lowest number will get priority

versus the channel with the

highest number.)

38

DMA Block scheme

• Each channel can handle DMA

transfers between a peripheral

register located at a fixed address

and a memory address.

• Peripheral and memory pointers can

optionally be automatically post-

incremented after each transaction.

• If incremented mode is enabled, the

address of the next transfer will be

the address of the previous one

incremented by 1, 2 or 4 depending

on the chosen data size.

39

DMA Block scheme

• Noncircular mode: no DMA

request is served after the last

transfer (that is once the number of

data items to be transferred has

reached zero).

• Circular mode: handle circular

buffers and continuous data flows

(e.g. ADC scan mode). When

circular mode is activated, the

number of data to be transferred is

automatically reloaded with the

initial value programmed during the

channel configuration phase, and the

DMA requests continue to be served.

40

DMA Channels

Each Stream is multiplexed up to eight channel, only one channel at a time can be active

It is not possible to activate two channels on the same stream

Is possible to perform transfers from all 8 streams

41

Code example

• We want to use a DMA and ADC to sample a signal from an input

channel.

• Configure and enable DMA

1. Configure and enable ADC

1. Configure the prescaler for ADCCLK

2. Configure and init the ADC (conversion mode, sampling time,

etc...)

3. Calibrate ADC

4. Starting the acquisition

ADC

1. Configure and enable DMA

#define ADCx_DR_Address ((uint32_t)0x4001204C)

DMA_InitTypeDef DMA_InitStructure;

/* Enable DMA2 clock*/

RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_DMA2, ENABLE);

/* DMA2 Stream0 channel 0 configuration */

DMA_InitStructure.DMA_Channel = DMA_Channel_0;

DMA_InitStructure.DMA_PeripheralBaseAddr = (uint32_t)&ADC1->DR;

DMA_InitStructure.DMA_Memory0BaseAddr = (uint32_t)&ADC1ConvertedValue;

DMA_InitStructure.DMA_DIR = DMA_DIR_PeripheralToMemory;

DMA_InitStructure.DMA_BufferSize = 1;

DMA_InitStructure.DMA_PeripheralInc = DMA_PeripheralInc_Disable;

DMA_InitStructure.DMA_MemoryInc = DMA_MemoryInc_Disable;

DMA_InitStructure.DMA_PeripheralDataSize = DMA_PeripheralDataSize_HalfWord;

DMA_InitStructure.DMA_MemoryDataSize = DMA_MemoryDataSize_HalfWord;

DMA_InitStructure.DMA_Mode = DMA_Mode_Circular;

DMA_InitStructure.DMA_Priority = DMA_Priority_High;

DMA_InitStructure.DMA_FIFOMode = DMA_FIFOMode_Disable;

DMA_InitStructure.DMA_FIFOThreshold = DMA_FIFOThreshold_HalfFull;

DMA_InitStructure.DMA_MemoryBurst = DMA_MemoryBurst_Single;

DMA_InitStructure.DMA_PeripheralBurst = DMA_PeripheralBurst_Single;

DMA_Init(DMA2_Stream0, &DMA_InitStructure);

/* Enable DMA1 channel0 */DMA_Cmd(DMA2_Stream0, ENABLE);

Address of the register where the result

of the acquisition is saved

ADC

1. Configure and enable DMA

#define ADCx_DR_Address ((uint32_t)0x4001204C)


/* Enable DMA2 clock*/

RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_DMA2, ENABLE);

/* DMA2 Stream0 channel 0 configuration */

















/* Enable DMA1 channel0 */DMA_Cmd(DMA2_Stream0, ENABLE);

ADC

We read 16bits from ADC and save

16bits in the ADC1ConvertedValue variable


ADC_InitTypeDef ADC_InitStructure;

ADC_CommonInitTypeDef ADC_CommonInitStructure;

/* Enable ADC1 clock*/

RCC_APB2PeriphClockCmd(RCC_APB2Periph_ADC1, ENABLE);

/* ADC Common Init */

ADC_CommonInitStructure.ADC_Mode = ADC_Mode_Independent;

ADC_CommonInitStructure.ADC_Prescaler = ADC_Prescaler_Div2;

ADC_CommonInitStructure.ADC_DMAAccessMode = ADC_DMAAccessMode_Disabled;

ADC_CommonInitStructure.ADC_TwoSamplingDelay = ADC_TwoSamplingDelay_5Cycles;

ADC_CommonInit(&ADC_CommonInitStructure);

/* ADC1 Init */

ADC_InitStructure.ADC_Resolution = ADC_Resolution_12b;

ADC_InitStructure.ADC_ScanConvMode = DISABLE;

ADC_InitStructure.ADC_ContinuousConvMode = ENABLE;

ADC_InitStructure.ADC_ExternalTrigConvEdge = ADC_ExternalTrigConvEdge_None;

ADC_InitStructure.ADC_ExternalTrigConv = ADC_ExternalTrigConv_T1_CC1;

ADC_InitStructure.ADC_DataAlign = ADC_DataAlign_Right;

ADC_InitStructure.ADC_NbrOfConversion = 1;

ADC_Init(ADC1, &ADC_InitStructure);

/* ADC1 regular channel12 configuration */

ADC_RegularChannelConfig(ADC1, ADC_Channel_12, 1, ADC_SampleTime_3Cycles);

/* Enable DMA request after last transfer (Single-ADC mode) */

ADC_DMARequestAfterLastTransferCmd(ADC1, ENABLE);

/* Enable ADC1 DMA */

ADC_DMACmd(ADC1, ENABLE);

/* Enable ADC1 */

ADC_Cmd(ADC1, ENABLE);

ADC












/* ADC1 Init */















/* Enable ADC1 */


ADC

ADC in independent mode












/* ADC1 Init */















/* Enable ADC1 */


ADC

Set the prescaler to have ADCCLK==18MHz












/* ADC1 Init */















/* Enable ADC1 */


ADC

ADC in Continuous Mode












/* ADC1 Init */















/* Enable ADC1 */


ADC

No trigger












/* ADC1 Init */















/* Enable ADC1 */


ADC

Number of Conversion












/* ADC1 Init */















/* Enable ADC1 */


ADC

We set the sampling time to 3 cycles












/* ADC1 Init */















/* Enable ADC1 */


ADC

Enabling DMA and ADC

#include "stm32f4xx.h"

#include "stm32f401_discovery.h"

#define ADCx_DR_ADDRESS ((uint32_t)0x4001204C)

/* Private macro -------------------------------------------------------------*/

/* Private variables ---------------------------------------------------------*/

volatile uint16_t ADC1ConvertedValue = 0;

volatile uint32_t ADCxConvertedVoltage = 0;

/* Private function prototypes -----------------------------------------------*/

/* Private functions ---------------------------------------------------------*/

static void ADC1_CH12_DMA_Config(void);

int main(void) {

int i=0;

/* ADC configuration */

ADC1_CH12_DMA_Config();

/* Start ADC Software Conversion */

ADC_SoftwareStartConv(ADC1);

while (1) {

ADCxConvertedVoltage = ADC1ConvertedValue *3300/0xFFF;

} }

ADC (code)

/** * @brief ADC3 channel07 with DMA configuration

* @note This function Configure the ADC peripheral

1) Enable peripheral clocks

2) DMA2_Stream0 channel2 configuration

3) Configure ADC Channel7 pin as analog input

4) Configure ADC3 Channel7

* @param None

* @retval None */

void ADC1_CH12_DMA_Config(void)

{




GPIO_InitTypeDef GPIO_InitStructure;

/* Enable ADC3, DMA2 and GPIO clocks ****************************************/

RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_DMA2 | RCC_AHB1Periph_GPIOC, ENABLE);


/* DMA2 Stream0 channel0 configuration **************************************/

















DMA_Cmd(DMA2_Stream0, ENABLE);

ADC (code)

/* Configure ADC1 Channel12 pin as analog input ******************************/

GPIO_InitStructure.GPIO_Pin = GPIO_Pin_2;

GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AN;

GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_NOPULL ;

GPIO_Init(GPIOC, &GPIO_InitStructure);

/* ADC Common Init **********************************************************/






/* ADC1 Init ****************************************************************/









/* ADC1 regular channel12 configuration *************************************/






/* Enable ADC1 */


}

ADC (code)

1. Qual’è il valore letto con l’ADC? Che significato ha?

2. Scrivere un programma che campiona il valore di un GPIO e

scrive il valore in SRAM utilizzando il DMA e lo stampa a video

tramite UART.

3. Scrivere un programma che monitora la temperatura ogni 30sec

e scrive il valore in SRAM utilizzando il DMA e lo stampa a video

tramite UART.

ADC (Esercizi e Domande)

Analog to Digital Conversion:

• Connect the potentiometer to the board:• 10K potentiometer

• External pin connected to 3.3V and GND

• Central pin connected to PC2

How to plot data on screen

• You can use Putty

• or you can use

Serialchart

to plot the data

• Set Baudrate

• Set com Port• Set data range (in the

example is (-1 1000))

How to plot data on screen

• Format data like in the example:

• Printf(“%d,%f,%f/r/n”,counter,data1,data2)

Microcontrollers: Lecture 6 Sensors, ADC,...

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