Introduction to ARM Assembly Language and Keil uVision4

Important Information

1.      In the lab room CL105, computers are running the operating
        system Windows 7 Enterprise, and ARM Software Microcontroller 
	Development Kit Version 4.71a (Keil uVision4) is installed. 

2.      To install it on your home computer, you can download the following file: 

        ~ftp/pub/class/301/ftp/mdk470a.exe


3.      To know more about Keil, visit  http://www.keil.com/

4.      To know more about the ARM Cortex-M family, visit  
		http://www.arm.com/products/processors/cortex-m/index.php

5. 	To see STM32VLDISCOVERT board, visit STM32VLDISCOVERY Board.

6.      To view Keil uVision4 Tutorials,  check the following:   
		Tutorial One
		Tutorial Two
		http://www.youtube.com/watch?v=zJncQKNDZv8

Create an ARM Assembly Language Program

To create an assembly language program, you need to use a text editor such as NotePad in Microsoft Windows environment. There is a text edit in the Keil uVision4 for you to use. The file name must have a .s at the end. Let's look at the following program called MyFirstArm.s on a PC. The file MyFirstArm.s contains the source code of the program to load registers and demonstrate a few other operations. We will use Keil uVision4 to create a project and execute this program so that you can get a feel of how Keil uVision4 works.

;The semicolon is used to lead an inline documentation
;This is the first ARM Assembly language program you see in the lab
;This program skeleton is from Dave Duguid and Trevor Douglas in summer 2013.
;When you write your program, you could have your info at the top document block
;For Example:  Your Name, Student Number, what the program is for, and what it does etc.

;;; Directives
          PRESERVE8
          THUMB       
 
; Vector Table Mapped to Address 0 at Reset
; Linker requires __Vectors to be exported
 
          AREA    RESET, DATA, READONLY
          EXPORT  __Vectors
 
__Vectors 
	  DCD  0x20001000     ; stack pointer value when stack is empty
          DCD  Reset_Handler  ; reset vector
  
          ALIGN
 
; The program
; Linker requires Reset_Handler
 
          AREA    MYCODE, CODE, READONLY
 
   	  ENTRY
   	  EXPORT Reset_Handler
 
 
Reset_Handler
;;;;;;;;;;User Code Starts from the next line;;;;;;;;;;;;

   	  MOV R0, #12
 
STOP  
	  ADD R0, R0, #4
   	  B  STOP
 
          END	;End of the program

1. A complete list of DIRECTIVES from ARM Information Center
2. Cortex-M3 Devices Generic User Guide

Start up Keil uVision4

You can start up uVision4 by clicking on the icon from the desktop or from the "Start" menu or "All Programs" on a lab PC.
The following screen is what you will see.

Create a project

Let's create our firt ARM uVision4 project now. To create a project, click on the "Project" menu from the uVision4 screen and select "New uVision Project...".
 

Then, select a folder, give project a name and save.
 

From the "Select Device for Target" window, select "STMicroelectronics" as the vendor.

click on "+" beside "STMicroelectronics" and then select "STM32F100RB" and click on "OK".

Make sure you click on "NO" for the following pop up window.

Create Source File

Save the program by clicking on the "Save" or "Save As" from the "File" menu and give it a name.

Add Source File to the Project

Select "Files of type" as "Asm Source file (*.s*;*.src*;*.a*), then select the file "FirstARM.s" for example.
Click on "Add", and then click on "Close".

Build your project

Run the program in your project

 
Click on "OK" for the pop up window showing "EVALUATION MODE, Running with Code Size Limit: 32K".

Open your uVision4 to full screen to have a better and complete view. The left hand side window shows you the registers and the right side window shows the program code. There are some other windows open. You may adjust the size of them to see better.
Run the program step by step, you can observe the change of the values in the registers.

Click on the "Start/Stop Debug Session" again to stop executing the program.

We will analyze the program and see how it works.
It works with both the simulated target and the real circuit board STM32VLDISCOVERY Board.
I will demonstrate it in the lab for you.

ARM Architecture

Here is a diagram of the ARM architecture for your reference.

    ARM Architecture is an Enhanced RISC Architecture.
    It has large uniform Register file and uses Load Store Architecture.
       i.e. operations operate on registers and not in memory locations.

    ARM Architecture instructions are of uniform and fixed length.
    It is a 32 bit processor. 
    It also has 16 bit variant called THUMB. 
       i.e. it can be used as 32 bit and as 16 bit processor.

ARM cores are licensed to partners/manufacturers so as to develop and fabricate new microcontrollers around same processor cores. A microcontroller is a small computer on a single integrated circuit containing a processor core, memory, and programmable input/output peripherals. The ARM Cortex-M3 microcontroller will be used in the lab with the STM32VLDISCOVERT board.
For more information, visit STM32VLDISCOVERY Board.

Here is another link to the ARM Archicheture for your reference.

ARM Registers

Here is the Register Organization in ARM State.

Here is the Register Organization in THUMB State.

Here is the Program Status Register Format:

	In ARM State, there are 16 general purpose registers;  
		      one or more status registers are accessible at any one time.

	In  THUMB State, there are 8 general purpose registers; 
			 PC, SP, LR and CPSR are accessible.
 
	Conditonion code flags in CPSR:
	N - Negative or less than flag
	Z - Zero flag
	C - Carry or bowrrow or extendedflag
	V - Overflow flag

ARM Instructions

 
	MOV 	R2, #0x76	
	; Move the 8-bit Hex number 76 to the low portion of R2

	MOV 	R2, #0x7654	
	; Move the 16-bit Hex number 7654 to the low portion of R2

	MOVT 	R2, #0x7654	
	; Move the 16-bit Hex number 7654 to the high portion of R2

	MOV32 	R2, #0x76543210		; Move the 32-bit Hex number 76543210 to the R2

	LDR	R2, = 0x76543210	; Load R2 with the 32-bit Hex number 76543210

	ADD	R1, R2, R3		; R1 = R2 + R3
	
	ADDS 	R1, R2, R3		; R1 = R2 + R3, and FLAGs are updated

	SUB	R1, R2, R3		; R1 = R2 - R3

	SUBS	R1, R2, R3		; R1 = R2 - R3, and FLAGs are updated

	B	LABEL			; Branch to LABEL

ARM Reference Card by Dr. Gerhard

Lab Assignment

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