77 lines
2.6 KiB
NASM
77 lines
2.6 KiB
NASM
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;// TI File $Revision: /main/4 $
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;// Checkin $Date: July 30, 2007 10:28:57 $
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;//###########################################################################
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;//
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;// FILE: DSP2833x_usDelay.asm
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;//
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;// TITLE: Simple delay function
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;//
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;// DESCRIPTION:
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;//
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;// This is a simple delay function that can be used to insert a specified
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;// delay into code.
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;//
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;// This function is only accurate if executed from internal zero-waitstate
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;// SARAM. If it is executed from waitstate memory then the delay will be
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;// longer then specified.
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;//
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;// To use this function:
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;//
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;// 1 - update the CPU clock speed in the DSP2833x_Examples.h
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;// file. For example:
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;// #define CPU_RATE 6.667L // for a 150MHz CPU clock speed
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;// or #define CPU_RATE 10.000L // for a 100MHz CPU clock speed
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;//
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;// 2 - Call this function by using the DELAY_US(A) macro
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;// that is defined in the DSP2833x_Examples.h file. This macro
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;// will convert the number of microseconds specified
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;// into a loop count for use with this function.
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;// This count will be based on the CPU frequency you specify.
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;//
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;// 3 - For the most accurate delay
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;// - Execute this function in 0 waitstate RAM.
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;// - Disable interrupts before calling the function
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;// If you do not disable interrupts, then think of
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;// this as an "at least" delay function as the actual
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;// delay may be longer.
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;//
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;// The C assembly call from the DELAY_US(time) macro will
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;// look as follows:
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;//
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;// extern void Delay(long LoopCount);
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;//
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;// MOV AL,#LowLoopCount
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;// MOV AH,#HighLoopCount
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;// LCR _Delay
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;//
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;// Or as follows (if count is less then 16-bits):
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;//
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;// MOV ACC,#LoopCount
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;// LCR _Delay
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;//
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;//
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;//###########################################################################
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;// $TI Release: DSP2833x/DSP2823x Header Files V1.20 $
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;// $Release Date: August 1, 2008 $
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;//###########################################################################
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.def _DSP28x_usDelay
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.sect ".text"
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.global __DSP28x_usDelay
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_DSP28x_usDelay:
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SUB ACC,#1
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BF _DSP28x_usDelay,GEQ ;; Loop if ACC >= 0
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LRETR
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;There is a 9/10 cycle overhead and each loop
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;takes five cycles. The LoopCount is given by
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;the following formula:
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; DELAY_CPU_CYCLES = 9 + 5*LoopCount
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; LoopCount = (DELAY_CPU_CYCLES - 9) / 5
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; The macro DELAY_US(A) performs this calculation for you
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;
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;//===========================================================================
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;// End of file.
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;//===========================================================================
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