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Laboratory Exercise #9 Assembly Language Solution
1 Introduction
In this lab you will incorporate an assembly language subroutine into a FreeRTOS task. Templates for the main FreeRTOS routine, a task, and an assembly language program will be provided to you. You will have to modify the task and assembly language program to compute the algebraic expressions assigned to you.
The algebraic expressions will have four input values. You will compute two intermediate values and then a result. The result may be dependent on the intermediate results. For example, your expressions might be:
X=A+(B+(C*D))+A;
Y=A+B+C+D;
if ( X = Y ) {
return( X );
} else {
return( Y );
}
Expressions can be assignment statements, if statements, or for statements. For this exercise we will not use constants.
2 References
The summary slides for the ARM ISA are at:
http://www.ittc.ku.edu/~gminden/Embedded_Systems/Lectures/EECS_388_ARM_Co rtexM3_ISA_B60329.pdf
The brief ARM description of the ISA is at:
http://www.ittc.ku.edu/~gminden/Embedded_Systems/PDFs/TI_Stellaris_ARM_Instr SetUm.pdf
The full description of the ARM assembler is at:
http://www.ittc.ku.edu/~gminden/Embedded_Systems/PDFs/TI_ARM_AssemblerMa nual.pdf
The slides I used in class are at:
http://www.ittc.ku.edu/~gminden/Embedded_Systems/Lectures/EECS_388_Subrotin eCalls_B30411.pdf and
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http://www.ittc.ku.edu/~gminden/Embedded_Systems/Lectures/EECS_388_Subrotin eCalls_B30411.pdf
Finally, a description of the ARM compiler is at:
http://www.ittc.ku.edu/~gminden/Embedded_Systems/PDFs/TI_ARM_CompilerMan ual.pdf
Valvano has numerous examples of assembly language and describes assembly language starting on page 90.
Actions
Make a project copy of your initial FreeRTOS823_LM3S_Prototype project from Laboratory #04.
Import “Task_AsmCompute.c” into your project. This task carries out the computation and calls your assembly language routine.
Import “AsmCompute.asm” into your project.
Modify the “Main_Blinky.c” to include a call to xCreateTask to add “Task_AsmCompute” to FreeRTOS.
Modify “Task_AsmCompute.c” and “AsmCompute.asm” to include the algebraic statements assigned to you.
Demonstrate your program.
The prototype source code for “Main_AsmCompute.c”, “Task_AsmCompute.c”, and “AsmCompute.asm” is available below.
The example code is also included below (formatting may vary).
The GTAs will assign individual computations.
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xTaskCreate( Task_AsmCompute, ( signed portCHAR * ) "AsmCompute", 512, NULL, 1, NULL );
//***************************************************************************** //
Call assembly language subroutine
// Author: Gary J. Minden
Organization: KU/EECS/EECS 388
//
Date:
2014-04-18
//
Version:
1.0
//
Purpose:
Call assembly language subroutine and check result
//
//
Notes:
//*****************************************************************************
#include "drivers/uartstdio.h"
#include "FreeRTOS.h"
#include "task.h"
#include "stdio.h"
//
Make the Task and Assembly language subroutines external (global)
extern void Task_AsmCompute( void *pvParameters ); extern int AsmCompute( int I1, int I2, int I3, int I4 );
//***************************************************************************** //
Task initialization
void Task_AsmCompute( void *pvParameters ) {
//*****************************************************************************
//
Constants and Variables #define MaxRange 10
Variables for testing assembly language subroutine
long int A, B, C, D;
long int CValue, AsmValue; unsigned long int Delay_2000mS;
Delay_2000mS = (2000 * configTICK_RATE_HZ ) / 1000;
while ( 1 ) {
for ( A = 0; A < MaxRange; A++ ) {
for ( B = 0; B < MaxRange; B++ ) {
for ( C = 0; C < MaxRange; C++ ) {
for ( D = 0; D < MaxRange; D++ ) {
//
You will replace the following statement with the
algebraic expressions assigned to you.
//
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CValue = A + B + C + D;
//
This is the invocation of your assembly language
subroutine to compute the same algebraic expression
AsmValue = AsmCompute( A, B, C, D );
//
Compare the C computation to the assembly language
computation and report discrepancies.
//
if ( CValue != AsmValue ) {
UARTprintf( "Boo! CValue: %d; AsmValue: %d\n", CValue,
AsmValue );
}
}
}
}
//
Log progress to the serial port
UARTprintf( "A: %d\n", A );
}
//
Report final results to indicate progress and completion.
UARTprintf( "Last CValue, AsmValue: %d, %d\n", CValue, AsmValue );
//
Delay for 2 seconds.
vTaskDelay( Delay_2000mS );
}
}
;;***************************************************************************** ;;
Assembly language subroutine
;; Author: Gary J. Minden
Organization: KU/EECS/EECS 388
;;
Date:
2014-04-18
;;
Version:
1.0
;;
Purpose:
Assembly language subroutine
;;
;;
Notes:
;;*****************************************************************************
;;
This subroutine computes a value based on four input arguments.
The arguments are assumed to be in CPU registers R0 - R3
(aka A1 - A4).
The result is returned in R0.
;;
;; Declare sections and external references
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.global AsmCompute ; Declare entry point as a global symbol
No constant data
No variable allocation
Program instructions
.text
; Program section
AsmCompute:
; Entry point
;;
Save necessary registers
Since this subroutine does not use registers other than R0 - R3,
and we do not call another subroutine, we don't need to save
any registers.
;;
;;
Allocate local variables on the Stack
Since this subroutine does not have local variables,
no Stack space need be allocated.
;;
;;
For demonstration, this subroutine computes R0 + R1 + R2 + R3
and returns the result in R0.
;;
You should replace the following three instructions with the
the instructions necessary to carry out your assigned
algebraic assignment statements.
;;
ADDS R0,R1
ADDS R0,R2
ADDS R0,R3
;;
Return from the subroutine with the result in R0
BX
LR
; Branch to the program address in
the Link Register
.end
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