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Lib/asm/DSP2833x_usDelay.asm

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+;// TI File $Revision: /main/4 $
+;// Checkin $Date: July 30, 2007   10:28:57 $
+;//###########################################################################
+;//
+;// FILE:  DSP2833x_usDelay.asm
+;//
+;// TITLE: Simple delay function
+;//
+;// DESCRIPTION:
+;//  
+;// This is a simple delay function that can be used to insert a specified
+;// delay into code.  
+;// 
+;// This function is only accurate if executed from internal zero-waitstate
+;// SARAM. If it is executed from waitstate memory then the delay will be
+;// longer then specified. 
+;// 
+;// To use this function:
+;//
+;//  1 - update the CPU clock speed in the DSP2833x_Examples.h
+;//    file. For example:
+;//    #define CPU_RATE 6.667L // for a 150MHz CPU clock speed
+;//    or #define CPU_RATE 10.000L // for a 100MHz CPU clock speed 
+;//
+;//  2 - Call this function by using the DELAY_US(A) macro
+;//    that is defined in the DSP2833x_Examples.h file.  This macro
+;//    will convert the number of microseconds specified
+;//    into a loop count for use with this function.  
+;//    This count will be based on the CPU frequency you specify.
+;//
+;//  3 - For the most accurate delay 
+;//    - Execute this function in 0 waitstate RAM.  
+;//    - Disable interrupts before calling the function
+;//      If you do not disable interrupts, then think of
+;//      this as an "at least" delay function as the actual
+;//      delay may be longer. 
+;//
+;//  The C assembly call from the DELAY_US(time) macro will
+;//  look as follows: 
+;//
+;//  extern void Delay(long LoopCount);                
+;//
+;//        MOV   AL,#LowLoopCount
+;//        MOV   AH,#HighLoopCount
+;//        LCR   _Delay
+;//
+;//  Or as follows (if count is less then 16-bits):
+;//
+;//        MOV   ACC,#LoopCount
+;//        LCR   _Delay
+;//
+;//
+;//###########################################################################
+;// $TI Release: DSP2833x Header Files V1.00 $
+;// $Release Date: September 7, 2007 $
+;//###########################################################################	
+
+       .def _DSP28x_usDelay
+       .text
+
+        .global  __DSP28x_usDelay
+_DSP28x_usDelay:
+        SUB    ACC,#1
+        BF     _DSP28x_usDelay,GEQ    ;; Loop if ACC >= 0
+        LRETR 
+
+;There is a 9/10 cycle overhead and each loop
+;takes five cycles. The LoopCount is given by
+;the following formula:
+;  DELAY_CPU_CYCLES = 9 + 5*LoopCount
+; LoopCount = (DELAY_CPU_CYCLES - 9) / 5
+; The macro DELAY_US(A) performs this calculation for you
+;
+;//===========================================================================
+;// End of file.
+;//===========================================================================