main.cpp

00001 #include "mbed.h"
00002 Serial pc(USBTX, USBRX);  //serial channel over HDK USB interface
00003 Timer timer;
00004 /************************************************************************//**
00005 * \file main.c
00006 * \brief LAB EXERCISE 5.2 - SQUARE ROOT APPROXIMATION
00007 *
00008 * Write an assembly code subroutine to approximate the square root of an 
00009 * argument using the bisection method. All math is done with integers, so the 
00010 * resulting square root will also be an integer
00011 ******************************************************************************
00012 * GOOD LUCK!
00013  ****************************************************************************/
00014 
00015  #include "stdint.h"
00016  
00017  
00018  /** @cond DO_NOT_INCLUDE_WITH_DOXYGEN */
00019  #include "string.h"
00020  /** @endcond */
00021  
00022  /**
00023  * @brief 5863 Write a brief description of the function here
00024  *
00025  * Detailed description of the function after one line gap
00026  *
00027  * @note You can also add a note this way
00028  *
00029  * @param[in] 
00030  *  You can also start writing on a new line. 
00031  *  And continue on the next line. This is how you describe an input parameter
00032  *
00033  * @return
00034  *  This is how you describe the return value
00035  * 
00036  */
00037  
00038 __asm int my_sqrt(int x){
00039     
00040     
00041     PUSH {R4-R7} ;
00042     LDR R1, =0      ;done = 0
00043     LDR R7, =0 ;a=0
00044     LDR R2, =0xFFFF ;b=2^31 -1
00045     LDR R3, =0xFFFFFFFF ;c=-1
00046 DO_WHILE
00047     MOV  R4, R3    ;c_old = c HERE R4 is being considered as c_old
00048     ADDS R5, R2, R7 ;R5 = a+b
00049     ASRS R5, R5, #1 ;R5 >> 1 which is nothing but (a+b/2) 
00050     MOV  R3, R5 ;c = (a+b)/2
00051     MOV  R6,R3
00052     MULS R6, R3, R6       ;R6 = c*c
00053     CMP  R6,R0 ;compare c*c and x (input integer)
00054     BEQ  DONE
00055     BLT LESS_THAN
00056     MOV  R2, R3 ;setting b=c
00057     B FINAL
00058 
00059 LESS_THAN
00060     MOV R7,R3 ;setting a=c
00061     B FINAL
00062 
00063 
00064 DONE
00065     LDR R1, =1 ;setting done = 1
00066     B FINAL ;return C
00067 
00068 
00069 FINAL
00070     CMP R1, #1 ;compare done = 1
00071     BEQ END
00072     BNE COMPARE
00073 
00074 
00075 COMPARE
00076     CMP R4, R3 ;compare c_old and c
00077     BNE DO_WHILE
00078     BEQ END
00079 
00080 
00081 END
00082     MOV R0, R3
00083     POP {R4-R7}
00084     BX LR
00085 }
00086 
00087 void printCpuCycles(double readValue, int number, int sqrt)
00088 {
00089     double cpuCycles = 0;
00090      
00091     cpuCycles = (readValue * 48000000);   // read value * frequqncy of clock
00092     pc.printf("Sqrt of %d using bisection menthod is %d \n\r", number, sqrt);
00093     pc.printf("Total time of execution for sqrt of(%d)is %f \n\r", number, readValue);
00094     pc.printf("Number of CPU cycles for sqrt(%d): %d\n\r\n\r", number, (int)cpuCycles);    
00095 }
00096 /*----------------------------------------------------------------------------
00097  MAIN function
00098  *----------------------------------------------------------------------------*/
00099  /**
00100  * @brief Main function
00101  *
00102  * Detailed description of the main
00103  */
00104 int main(void){
00105     
00106     volatile int r, j=0;
00107     
00108     double timer_read = 0.0;
00109     double sum = 0;   
00110     
00111     pc.printf("/*----------------------------------------------------------------------------*/\r\n\r\n");
00112     pc.printf("Frequency of KL25Z (ARM Cortex M0+): 48 MHZ\n\r\n\r");
00113     
00114     timer.start();
00115     
00116     timer.reset();
00117     r = my_sqrt(2);     // should be 1
00118     timer_read = timer.read();
00119     printCpuCycles(timer_read, 2, r);  
00120     sum = sum + timer_read;
00121     timer.reset();
00122     
00123     
00124       
00125     r = my_sqrt(4);    // should be 2
00126     timer_read = timer.read();
00127     printCpuCycles(timer_read, 4, r); 
00128     sum = sum + timer_read; 
00129     timer.reset(); 
00130     
00131 
00132          
00133     r = my_sqrt(22);    // should be 4
00134     timer_read = timer.read();
00135     printCpuCycles(timer_read, 22, r);  
00136     sum = sum + timer_read;
00137     timer.reset();  
00138     
00139     r = my_sqrt(121);   // should be 11
00140     timer_read = timer.read();
00141     printCpuCycles(timer_read, 121, r);  
00142     sum = sum + timer_read;
00143     
00144     pc.printf("Total time of operation: %f\n\r\n\r", sum);
00145     sum = sum * 48000000;
00146     pc.printf("CPU cycles: %d\n\r\n\r", (int)(sum));
00147     
00148     pc.printf("/*----------------------------------------------------------------------------*/\r\n\r\n"); 
00149 
00150 }
00151 
00152 // *******************************ARM University Program Copyright © ARM Ltd 2014*************************************/
00153