eeng449b/savvides lec 6.1 2/1/05 feb 1, 2005 prof. andreas savvides spring 2005 g449b eeng...

EENG449b/SavvidesLec 6.1

2/1/05

Feb 1, 2005

Prof. Andreas Savvides

Spring 2005

http://www.eng.yale.edu/courses/2005s/eeng449b

EENG 449b/CPSC 439b Computer Systems

Lecture 6

ARM Architecture & Programming


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Where is ARM Today?


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Announcements

• Need to register for lab access• Lab located in CO-40• You need to see Ed Jackson to get

access to the lab– Take your Yale id with you

• Reading for next lecture– Get by without and RTOS by Melkonian

• Camera based projects:– Camera description lecture tomorrow – Prof. Eugenio Culurciello, AKW 000 @ 4:00pm


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Not the case when you have loads and stores!!!!


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3-State ARM7 Pipeline


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Stalls in 3-stage pipeline


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How do we improve the design?

• Where are the bottlenecks? • In the memory subsystem: we have a

Von Neumann Architecture– Include separate Instruction and Data Caches

• How do we minimize stalls from data dependencies?

– ?

• When does this solution not work?• Load instructions

LDR rN, [..]ADD r2, r1, rN


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5-stage ARM9Improvement


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ARM Instructions

3-type instruction classification• Data processing• Data transfer• Control flow


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Data Processing Instructions

• Arithmetic operationsADD r0, r1, r2;ADC r0, r1, r2; add w/curry r0 :=r1+r2+cSUB r0, r1, r2; SBC r0, r1, r2; r0 :=r1 – r2 + C – 1etc …

• Bitwise Logical OperationsAND r0, r1, r2OR r0, r1, r2EOR r0, r1, r2BIC r0, r1, r2; r0 := r1 and not r2


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Data Processing Instructions II

• Register Movement Operations

MOV r0, r2; r0 := r2

MVN r0, r2;r0 := not r2• Comparison Operations

CMP r1, r2 ; set cc on r1 – r2

CMN r1, r2;set cc on r1 + r2

TST r1, r2; set cc on r1 and r2

TEQ r1, r2; set cc on r1 xor r2• Immediate Operands

ADD r3, r3, #1; r3 := r3 + 1

AND r8, r7, #&ff;


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Data Transfer Instructions

• Most common are load and store but there is support for multiple loads,

• Register Indirect Addressing

LDR r0, [r1]

STR r0, [r1]

LDR r0, [r1,#4]

LDR r0, [r1,#4]! ; also increments r1 ; by the immediate


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Control Flow Instructions

• Unconditional BranchesB LABEL…

LABEL …

• Conditional BranchesMOV r0, #0

LOOP …ADD r0, r0, #1CMP r0, #10BNE LOOP…


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Writing a simple assembly language program


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Reverse Engineering a Program

• In the lab we will be using the GNU tools

– Slight difference in syntax

• As a first step we will compile and analyze programs

– Main compiler arm-elf-gcc– To compile a program to assembly

» arm-elf-gcc –S hello.c– Using objdump

» Arm-elf-objdump –source hello


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Example Program#include <stdio.h>int a_global = 10;int foo (int arg ){

static foo_counts = 0; foo_counts++; return foo_counts + arg;}int main (void){

int nloops;char* charstr = "hello world\n";

for( nloops=0; nloops < 10; nloops ++){printf("%s",charstr);foo(nloops);

}return 0;

}


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An Example Embedded System Application: A Mobile Terminal

Processor

LCD DisplayKeyboard

Serial PortRS232

Radio

Bar-code Scanner

(IO_Scan)

Receipt Printer


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Minimal Mobile Terminal Program

int main(void) {

Init_All(); for (;;) {

IO_Scan(); // bar-code scanner

IO_ProcessOutputs(); KBD_Scan(); // keyboardPRN_Print(); // printerLCD_Update(); // displayRS232_Receive(); // serial portRS232_Send(); TIMER_Process(); // timer

} // should never ever get here

}


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Minimal Mobile Terminal Program

int main(void) {

Init_All(); for (;;) {

IO_Scan(); IO_ProcessOutputs(); KBD_Scan(); PRN_Print(); LCD_Update();

RS232_Receive(); RS232_Send();

TIMER_Process(); } // should never ever get here

}

•Each function is an independent task•Tasks should return in a reasonable time•Frequency of main loop execution is non-deterministic•Tasks are event-driven

– Tasks do not execute unless a suitable message is received


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Task Requirements

• Some tasks are periodic– Blink the LCD cursor once every second

• Tasks may not need to run at the same frequency

• Some tasks may be event triggered– RS-232 receive only needs to execute of there is a

character received– PRN_Print() only needs to execute when a receipt is

required

• Need a method to communicate between tasks


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Event Driven Tasks & Task Communication

Task 3

Task 1

Task 2

Task Event Queue

Task3_PutEvent()

Task3_PutEvent()

Task3_GetEvent()


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Task Execution Frequency

• Different tasks may need to execute at different frequencies OR

• Task execution frequency may change during the lifetime of an application

• Example:• You may not need to refresh the

LCD every 1ms if the information to be displayed does not change

• You may not want to delay execution of other tasks too long


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State-Driven LCD Driver(from Melkonian)

void Window_Update(void) { switch (WinTaskState) { case WIN_TASK_IDLE: return; case WIN_TASK_CONST: UpdateWinConst(); WinTaskState++; break; case WIN_TASK_VARS: UpdateWinVars(); WinTaskState++; break; case WIN_TASK_GRAPH:

UpdateWinGraph(); WinTaskState++;

break; }}


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Software Timers

• Timers are needed to provide multitasking ability to your software

• Need to schedule a large number of periodic or single shot events

– Blinking cursor– Flashing leds– Be able to put your device to sleep after some

idle time– Timers in the implementation of communication

protocols

• You could use hardware timers for some tasks BUT

– There is a very limited number of hardware timers compared to the needs of an application


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Designing a Software TimerTasks deposit theirevents in a queue

Application handler functions

Software timer processHandler for the hardware 10ms timer check Delta Queue

For expired timers


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Using A Software Timer

• word TMR_InstallTimeoutHandler(word timer_handle, void(*timeout_func)(word, dword))

• word TMR_Start(word timer_handle, word timeout, dword parameter);

• word TMR_Stop(word timer_handle);


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Features of RTOS (hard)

• Structure - OS components and user defined Tasks

• Multi-tasking• Provides hard time guarantee

– Schedulability test guarantees task deadline

• Priority Support– Pre-emption of tasks


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Drawbacks of RTOS

• Interrupt latency of context switching may introduce inefficiency

• Pre-emption requires extra attention to shared memory

• Multi-tasking requires private stack for each task.

• RTOS is difficult to debug• Commercial RTOS

– Portability can be difficult– License Fee– Learning Curve


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Next-time

• Programming assignment 1

eeng449b/savvides lec 6.1 2/1/05 feb 1, 2005 prof. andreas savvides spring 2005 g449b eeng...

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