ARTIST2 ARTIST2 Graduate Course on Embedded Systems RT-Linux - - PowerPoint PPT Presentation

▶
artist2 artist2
SMART_READER_LITE
LIVE PREVIEW

ARTIST2 ARTIST2 Graduate Course on Embedded Systems RT-Linux - - PowerPoint PPT Presentation

Sep 17, 2022 432 likes •646 views

ARTIST2 ARTIST2 NoE on Embedded Systems Design ECS Graduate Course Valencia, Spain. April 58, 2005 ARTIST2 ARTIST2 Graduate Course on Embedded Systems RT-Linux Motor Controller Michal Sojka, Ondej pinka Department of Control

slide-1
SLIDE 1

ARTIST2 ARTIST2

NoE on Embedded Systems Design – ECS Graduate Course Valencia, Spain. April 5­8, 2005

­ 1 ­

RT-Linux Motor Controller

Michal Sojka, Ondřej Špinka Department of Control Engeneering Faculty of Electrical Engeneering Czech Technical University

ARTIST2 ARTIST2

Graduate Course on Embedded Systems

slide-2
SLIDE 2

ARTIST2 ARTIST2

NoE on Embedded Systems Design – ECS Graduate Course Valencia, Spain. April 5­8, 2005

­ 2 ­

DC Motor Controller in RT-Linux

The goal is to create a controller which controls the speed of the motor.

slide-3
SLIDE 3

ARTIST2 ARTIST2

NoE on Embedded Systems Design – ECS Graduate Course Valencia, Spain. April 5­8, 2005

­ 3 ­

Description of the Model

slide-4
SLIDE 4

ARTIST2 ARTIST2

NoE on Embedded Systems Design – ECS Graduate Course Valencia, Spain. April 5­8, 2005

­ 4 ­

Steps to Create a Controller

  • 1. Create a basic RT­Linux module.
  • 2. Try to rev up the motor at full speed.
  • 3. Write a thread generating PWM signal (period 1 ms)
  • 4. Write an IRQ handler (position measuring).
  • 5. Write a thread measuring the speed.
  • 6. Implement a velocity controller (PID).
  • 7. Enable communication with user­space.
  • 8. Write a user­space interface for the controller.
slide-5
SLIDE 5

ARTIST2 ARTIST2

NoE on Embedded Systems Design – ECS Graduate Course Valencia, Spain. April 5­8, 2005

­ 5 ­

Steps to Create a Controller

  • 1. Create a basic RT­Linux module.
  • 2. Try to rev up the motor at full speed.
  • 3. Write a thread generating PWM signal (period 1 ms)
  • 4. Write an IRQ handler (position measuring).
  • 5. Write a thread measuring the speed.
  • 6. Implement a velocity controller (PID).
  • 7. Enable communication with user­space.
  • 8. Write a user­space interface for the controller.
slide-6
SLIDE 6

ARTIST2 ARTIST2

NoE on Embedded Systems Design – ECS Graduate Course Valencia, Spain. April 5­8, 2005

­ 6 ­

A Basic RT-Linux Module

 Source: simple.c  Makefile for compilation

#include <linux/module.h> #include <linux/kernel.h> int init_module(void) { printk("Init\n"); return 0; } void cleanup_module(void) { printk("Cleanup\n"); } MODULE_LICENSE("GPL"); all: simple.o include /usr/rtlinux/rtl.mk include $(RTL_DIR)/Rules.make shell# insmod simple.o

Running the application:

 The same kind of module Linux uses to implement drivers etc.  The code runs in the kernel­space (shares both code and data with

the Linux kernel).

slide-7
SLIDE 7

ARTIST2 ARTIST2

NoE on Embedded Systems Design – ECS Graduate Course Valencia, Spain. April 5­8, 2005

­ 7 ­

Parallel Port

 Motor rotation:

– left: outb(1, 0x378); – right: outb(2, 0x378);

 IRC signals:

– inb(0x379);

IRQ PWM: bits 0, 1

IRC {

IRC

0x379 0x378

0x37a PWM (left, right) IRQ

slide-8
SLIDE 8

ARTIST2 ARTIST2

NoE on Embedded Systems Design – ECS Graduate Course Valencia, Spain. April 5­8, 2005

­ 8 ­

Periodic Threads

#define MS (1000000) void *thread_func(void *arg) { pthread_make_periodic_np(pthread_self(), gethrtime(), 2*MS); while (1) { /* do something */ pthread_wait_np(); } return NULL; } int init_module(void) { pthread_t thr; pthread_create(&thr, NULL, &thread_func, NULL); return 0; }

start time

period wait for the start of the next period

slide-9
SLIDE 9

ARTIST2 ARTIST2

NoE on Embedded Systems Design – ECS Graduate Course Valencia, Spain. April 5­8, 2005

­ 9 ­

PWM Generation

 The value of the variable action specifies the control action.  Use the usleep function to suspend the thread for given

number of microseconds.

 The PWM period should be about 1 ms. This is due to the

RT­Linux scheduling error (~10 us).

while (1) { set_output (1); usleep ( action * TPWM ); set_output (0); pthread_wait_np (); }

TPWM TPWM

slide-10
SLIDE 10

ARTIST2 ARTIST2

NoE on Embedded Systems Design – ECS Graduate Course Valencia, Spain. April 5­8, 2005

­ 10 ­

Thread Priorities

 Rate Monotonic Priority Assignment

– the lesser task period the higher assigned priority

 In RT-Linux: The higher number the higher priority

int init_module(void) { pthread_attr_t attr; struct sched_param param; pthread_attr_init(&attr); param.sched_priority = 1; pthread_attr_setschedparam(&attr, &param); pthread_create(&thr, &attr, &thread_func, NULL); return 0; }

the priotity of the thread

slide-11
SLIDE 11

ARTIST2 ARTIST2

NoE on Embedded Systems Design – ECS Graduate Course Valencia, Spain. April 5­8, 2005

­ 11 ­

IRQ Handling

 Parallel port: IRQ 7  Interrupts reception should be reenabled in the

handler!

 Enable interrupt generation by setting a bit in

parallel port control register: outb(0x10, 0x37a);

unsigned int irq_handler(unsigned int irq, struct pt_regs * regs) { /* do something */ rtl_hard_enable_irq(irq); return 0; } status = rtl_request_irq(irq_number, irq_handler);

slide-12
SLIDE 12

ARTIST2 ARTIST2

NoE on Embedded Systems Design – ECS Graduate Course Valencia, Spain. April 5­8, 2005

­ 12 ­

Signals From an IRC sensor

 Whenever the value of any IRC sensor channel

changes, electronics in the motor generates the IRQ.

 The motor is equipped by IRC with 100 pulses per turn

and there are 4 IRQs per one step. So there are 400 IRQs per turn.

channel A channel B IRQ channel C (IRQ)

slide-13
SLIDE 13

ARTIST2 ARTIST2

NoE on Embedded Systems Design – ECS Graduate Course Valencia, Spain. April 5­8, 2005

­ 13 ­

PID Controller

PID controller Motor + –

Desired value Speed Voltage (PWM duty cycle)

yk=P⋅ekI⋅∑

i=0 k−1

eiD⋅ ek−ek−1

ek yk

e = motor->reference - motor->velocity

slide-14
SLIDE 14

ARTIST2 ARTIST2

NoE on Embedded Systems Design – ECS Graduate Course Valencia, Spain. April 5­8, 2005

­ 14 ­

Fixed Point Arithmetic

 We need to use decimal numbers in calculations  For this simple task we don't need to use a

mathematical coprocessor. Smaller processors don't have any coprocessor.

5.0 ~ 0x500, 2.5 ~ 0x280

Addition: 5.0 + 2.5 ~ 0x500 + 0x280 = 0x780 ~ 7.5

Multiplication: 5.0 * 2.5 ~ 0x500 >> 4 * 0x280 >> 4 = 0x50 * 0x28 = 0xC80 ~ 12.5

int (32 bit) Integer part (24 bit) Decimal part (8 bit)

slide-15
SLIDE 15

ARTIST2 ARTIST2

NoE on Embedded Systems Design – ECS Graduate Course Valencia, Spain. April 5­8, 2005

­ 15 ­

RT FIFOs

 Communication between RT­Linux and user­space.  Unidirectional communication, for bidirectional

communication we need two fifos.

#include <rtl_fifo.h> int fifo = 0; rtf_create(fifo, 1000); rtf_create_handler(fifo, &read_handler); retval = rtf_put(fifo, &variable, sizeof(variable)); int read_handler(unsigned int fifo) { int reference; rtf_get(fifo, &reference, sizeof(reference)); return 1; }

RT­Linux side We use the FIFO number 0

slide-16
SLIDE 16

ARTIST2 ARTIST2

NoE on Embedded Systems Design – ECS Graduate Course Valencia, Spain. April 5­8, 2005

­ 16 ­

RT FIFOs – User-Space Side

int i, j; if ((fifo_out = open("/dev/rtf0", O_WRONLY)) < 0) { perror("/dev/rtf0"); exit(1); } write(fifo_out, &i, sizeof(i)); read(fifo_in, &j, sizeof(j)); We use the FIFO number 0

 From the user­space a FIFO looks like an ordinary file.

slide-17
SLIDE 17

ARTIST2 ARTIST2

NoE on Embedded Systems Design – ECS Graduate Course Valencia, Spain. April 5­8, 2005

­ 17 ­

How to Start

 In the first boot menu chose ARTIST2Linux  In the second RTLinux (2.4.24-rtl)  Log in as root, password realtime  Go to the directory (you should be already there)

cd /root/artist2/artist2-motor-rtl/src

 Start RT Linux: rtlinux start  Compile the application: make  Load both real­time and user­space part of the

application: ./load_app_gui

slide-18
SLIDE 18

ARTIST2 ARTIST2

NoE on Embedded Systems Design – ECS Graduate Course Valencia, Spain. April 5­8, 2005

­ 18 ­

Content of Directories

 src – the code for real­time part

– motor.c – the code of application (you will modify this file) – motor.h – common declarations for both RT and US part – Makefile – commands for compilation. – load_app_gui – script for starting the application

 qtmotor – graphical user­space interface  curmotor – text­based user­space interface

slide-19
SLIDE 19

ARTIST2 ARTIST2

NoE on Embedded Systems Design – ECS Graduate Course Valencia, Spain. April 5­8, 2005

­ 19 ­

 Extend the PWM thread to generate PWM signal

based on the value motor->action.

 Implement a controller.

– start with a P­controller which computes action as action = KP * (reference – velocity) – Experiment to find the value of KP – Extend the controller to PI. In the simplest case, you'll need to store the sum of errors.

 You may try to do other extensions – windup handling,

use fixed­point arithmetic, use better implementation of PID, etc.

Your Tasks

slide-20
SLIDE 20

ARTIST2 ARTIST2

NoE on Embedded Systems Design – ECS Graduate Course Valencia, Spain. April 5­8, 2005

­ 20 ­

Debugging

 Inside the code use the rtl_printf() function to print the

values you are interested in.

rtl_printf(“Value of action: %d\n”, action);

 You can see those messages using “dmsg” command.