2023 1 embedded systems chapter 3 1

3.1 Raspberry GPIO▪ Chú ý:▪ Tất cả các chân I/O hỗ trợ ngắt▪ Tất cả các chân đều có điện trở kéo lên và kéo xuống bên trong▪ Một số chân có thể chia sẻ chức năng▪ Lưu ý:▪ Đoản mạch kết n

HỆ THỐNG NHÚNG

Dr Thanh Nguyen

Email: thanh.nguyenngoc@phenikaa-uni.edu.vn Office: Room 606 - Building A4

Chương 3: LẬP TRÌNH NHÚNG VỚI RASPBERRY

3.1 Raspberry GPIO

▪ Có hai hệ thống đánh số cho các chân GPIO.

▪ Đánh số vật lý (dễ hiểu) cho biết vị trí để chân GPIO trên board R.Pi

▪ Đánh số theo chân bộ xử lý BCM2837.

3.1 Raspberry GPIO

▪ Chú ý:

▪ Tất cả các chân I/O hỗ trợ ngắt

▪ Tất cả các chân đều có điện trở kéo lên và kéo xuống bên trong

▪ Một số chân có thể chia sẻ chức năng

Truy cập phần cứng vs Linux

▪ Giao tiếp giữa phần cứng và phần mềm là

rất quan trọng.

▪ Giao tiếp được xử lý bằng cách sử dụng

thanh ghi thiết bị phần cứng được ánh xạ

Truy cập phần cứng vs Linux

▪There are many ways to implement hardware/software bridge

▪Create a device node in /dev

▪Access device via virtual file system sysfs

Điều khiển GPIO dùng sysfs

▪ sysfs provide a virtual file system for device access at /sys/class

▪ Using sysfs, GPIO can be control in Shell language

▪ Functions:

▪ Export the particular GPIO pin for user control

echo 30 > /sys/class/gpio/export

▪ Change the GPIO pin direction to in/out

echo "out" > /sys/class/gpio/gpio30/direction

echo “in" > /sys/class/gpio/gpio30/direction

▪ Change the value

echo 1 > /sys/class/gpio/gpio30/value

echo 0 > /sys/class/gpio/gpio30/value

▪ Unexport the GPIO pin

echo 30 > /sys/class/gpio/unexport

Điều khiển GPIO dùng sysfs

▪Example: Create a file name blink.sh

▪Run the code with command: /blink.sh

Thư viện WiringPi

▪WiringPi is a GPIO access library for Raspberry

▪ wiringPi is writte in C and preinstalled in raspbian

▪ Website: https://wiringpi.com

▪ Install: git clone https://github.com/WiringPi/WiringPi.git

▪Features:

▪ Support command-line GPIO control in terminal

▪ Support digital/analog reading and writing

▪ Support wired communication: SPI, I2C

▪ Provide software/hardware PWM

▪ Support external interrupts, delay.

Thư viện WiringPi

▪gpio –v : prints wiringPi version

▪ gpio mode <pin> in/out/pwm/clock/up/down/tri :sets the

mode for a pin

▪gpio write <pin> 0/1 : sets an output pin to high (1) or low (0)

▪gpio read <pin> : Reads and prints the logic value of the given pin

▪gpio edge <pin> rising/falling/both/none : enables the given pin

for edge interrupt triggering

Thư viện WiringPi

▪gpio readall : reads all the normally accessible pins and prints a

table of their numbers

Thư viện WiringPi

▪wiringPiSetupPhys () : initialize WiringPi library

▪pinMode (int pin, int mode) : sets the mode of a pin

▪digitalWrite (int pin, int value) : Writes the value HIGH or LOW (1

or 0) to the given pin

▪digitalRead (int pin) : returns the value read at the given pin

▪analogRead (int pin) : returns the value read on the supplied

analog input pin

Điều khiển GPIO dùng WiringPi

▪ Compile and run the blink program

gcc –Wall –o blink blink.c –lwiringPi

./blink

▪ The program will run forever, stop it with Ctrl-C

KẾT NỐI MẠCH CÔNG SUẤT

Pulse Width Modulation

PWM

Ngắt dùng WiringPi

▪ Structure of an interrupt program

Các chuẩn giao tiếp

Các chuẩn giao tiếp song song

Giao tiếp nối tiếp

SPI - Serial Peripheral Interface

▪ SPI uses separate lines for

data and a “clock” that keeps

both sides in perfect sync

▪ Only one way direction bus

▪ SDO/MOSI (Signal Data

Out/Master Out Slave In)

▪ SDI/MISO (Signal Data

In/Master In Slave Out)

▪ SCK (System Clock)

SPI - Serial Peripheral Interface

▪ In SPI, only one side generates the clock signal (usually called

CLK or SCK for Serial Clock)

▪ The side that generates the clock is called the “master”, and the

other side is called the “slave”

SPI connection

▪ Raspberry Pi is equipped with two SPI bus: SPI0 and SPI1

SPI - Serial Peripheral Interface

34

SPI - Serial Peripheral Interface

▪ How do you send data back

from slaves to master?

▪ Master always generates the

clock signal

▪ MCU must know in advance

when a slave needs to return

data and how much data will

be returned

SPI - Serial Peripheral Interface

▪ MCU tells a slave that it

should wake up and

receive/send data via Slave

select (SS) line

▪ SS = 1 : disconnects the slave

from the SPI bus

▪ SS = 0 activates the slave

SPI - Serial Peripheral Interface

▪ Simple protocol, 1 bit /1 clock

▪ High speed (<32MHz)

▪ Short distance (<1m), need

amplifier for long distance >10m

SPI Serial Frame Format

▪ SPI Serial Frame Format is selected based on connected devices

▪ The SPI interface format can be configured with

▪ Clock Polarity – CPOL

▪ Clock Phase – CPHA

▪ Clock Polarity Bit – CPOL

▪ Clock Polarity = 0, the SCK line idle state is LOW

▪ Clock Polarity = 1, the SCK line idle state is HIGH

▪ Clock Phase Bit – CPHA

▪ Clock Phase = 0, the data is sampled on the first SCK clock transition

▪ Clock Phase = 1, the data is sampled on the second SCK clock transition.

SPI Serial Frame Format

▪ CPOL = 0, CPHA = 0

SPI Serial Frame Format

▪ CPOL = 0, CPHA = 1

▪ SEL signal must remain active until the last data transfer has completed.

SPI Serial Frame Format

▪ CPOL = 1, CPHA = 0

▪ SEL signal must change to an inactive level between each data frame.

SPI Serial Frame Format

▪ CPOL = 1, CPHA = 1

▪ SEL signal must remain active until the last data transfer has completed.

SPI Serial Frame Format

▪ nRF24L01: Digital interface (SPI) speed 0-8 Mbps.

SPI connection

▪ nRF24L01

SPI connection

▪ Raspberry Pi is equipped with two SPI bus: SPI0 and SPI1

SPI connection

▪ WiringPi includes a library for Raspberry Pi’s SPI interface

▪ To use SPI interface, follow these steps:

▪ Step 1: load the SPI drivers into the kernel with command:

gpio load spi

▪ Step 2: In C file, include the wiringPi SPI library with

#include <wiringPiSPI.h>

▪ Step 3: Initialize SPI with:

wiringPiSPISetup (int channel, int speed) channel : 0 or 1; speed in range 500kHz through 32MHz

▪ Step 4: transfer data with :

wiringPiSPIDataRW (int channel, unsigned char *data, int len);

▪ Data that was in buffer is overwritten by data returned from the SPI bus

SPI Example