wait.c

// Wait functions
// Jason Losh

//-----------------------------------------------------------------------------
// Hardware Target
//-----------------------------------------------------------------------------

// Target uC:       TM4C123GH6PM
// System Clock:    40 MHz

//-----------------------------------------------------------------------------
// Device includes, defines, and assembler directives
//-----------------------------------------------------------------------------

#include <stdint.h>
#include "tm4c123gh6pm.h"
#include "wait.h"

//-----------------------------------------------------------------------------
// Subroutines
//-----------------------------------------------------------------------------

// Approximate busy waiting (in units of microseconds), given a 40 MHz system clock
void waitMicrosecond(uint32_t us)
{
	__asm("WMS_LOOP0:   MOV  R1, #6");          // 1
    __asm("WMS_LOOP1:   SUB  R1, #1");          // 6
    __asm("             CBZ  R1, WMS_DONE1");   // 5+1*3
    __asm("             NOP");                  // 5
    __asm("             NOP");                  // 5
    __asm("             B    WMS_LOOP1");       // 5*2 (speculative, so P=1)
    __asm("WMS_DONE1:   SUB  R0, #1");          // 1
    __asm("             CBZ  R0, WMS_DONE0");   // 1
	__asm("             NOP");                  // 1
    __asm("             B    WMS_LOOP0");       // 1*2 (speculative, so P=1)
    __asm("WMS_DONE0:");                        // ---
                                                // 40 clocks/us + error
}