Motorola DSP56305 Manuel d'utilisateur Page 31
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- Table des matières
- MARQUE LIVRES
Noté. / 5. Basé sur avis des utilisateurs
3-2 Optimizing DSP56300/DSP56600 Applications MOTOROLA
Program Control
Hardware Loops
A common programming technique is known as “loop unrolling”,
in which a high-level loop is replaced by the inner loop code,
repeated N times, thus saving the time needed to decrement the
counter, test for the end of the loop, and jumping back to the top.
From the above explanation, it follows that this technique is less
efficient in the DSP56300/DSP56600 family—the hardware executes
loops normally at the same speed as unrolled code (except for the
initializing DO instruction itself, which takes 5 cycles). Loops
should be unrolled only when the 5-cycle initialization is
meaningful in comparison to the total loop length, especially if this
loop is nested in another loop and the 5-cycle delay is multiplied.
See the example in Section 7.1.1 on page 7-1.
High-level “for” loops are normally implemented in assembly with
the DO instruction. The instructions DO FOREVER and BRKcc
(break on condition) may be used to implement high-level “while”
or “repeat” loops efficiently. The following example is a wave
generator that sends data to a peripheral (Host Interface HI08 in this
example) until a hardware interrupt (IRQA
) sets a flag, signalling
the end of the loop. The core drives the HI08 transmitter by polling
the HTDE (Host Transmitter Data Empty) bit in the HI08 status
register. The C high-level code may look like:
while (!flag){
a1 = next_wave_value();
wait_until_transmitter_empty();
send_data(a1);
}
and in Assembler:
org p:I_IRQA ;IRQA_ interrupt vector
bset #0,x:<FLAG ;occupies 2 words
org p:MAIN_PROGRAM
...
move #0,x0
move x0,x:FLAG ;clear FLAG register
bclr #0,sr ;clear carry bit
do forever,_END_LOOP
brkcs ;break loop if carry bit set
jsr NEXT_WAVE_VALUE;new value returned in a1
_WAIT
jclr #0,x:M_SSR,_WAIT;wait until transmitter empty
btst #0,x:FLAG ;set carry by flag value
movep a1,x:M_HTX ;transmit data to host.
_END_LOOP
- DSP56300/DSP56600 1
- Digital Signal 1
- Processors 1
- TABLE OF CONTENTS 2
- LIST OF FIGURES 6
- LIST OF TABLES 7
- INTRODUCTION 8
- 1.2 DSP56600 CORE FAMILY 9
- Table 1-1 11
- Introduction 12
- Description and Use 13
- Application Note Structure 14
- 1.4.3 Appendixes 15
- DATA OPERATIONS 16
- DSP56300 Family Manual 21
- 2.3 THE MAX INSTRUCTION 22
- 2.4 USING THE BARREL SHIFTER 23
- Data Operations 24
- Using the barrel shifter 24
- DSP56300 26
- DSP56600 Family 26
- Double precision arithmetic 27
- INSTRUCTIONS 28
- PROGRAM CONTROL 30
- Program Control 31
- Hardware Loops 31
- 3.2 THE HARDWARE STACK 32
- DSP56600 Family Manuals 35
- 3.3 USING THE STACK EXTENSION 36
- Using the Stack Extension 37
- EXTENSION 39
- Conditional DALU Instructions 40
- 3.6 PC RELATIVE INSTRUCTIONS 42
- DSP56600 Family Manual 43
- 3.7 USING FAST INTERRUPTS 46
- Using Fast Interrupts 48
- USING THE DMA 50
- Using the DMA 51
- Using Slow, Low-Cost Memories 54
- 4.4 SERVICING A PERIPHERAL 55
- Servicing a Peripheral 56
- Section 5 62
- 5.1 THE INSTRUCTION CACHE 62
- 5.1.1 Cache Sectors 64
- The Instruction Cache 65
- 5.1.3 Cache Burst Mode 67
- 5.2 MEMORY SWITCH 70
- Memory Switch 71
- 5.3 USING THE BOOTSTRAP ROM 72
- Using the Bootstrap ROM 73
- PIPELINE INTERLOCKS 74
- Pipeline Interlocks 75
- Data ALU Pipeline Interlocks 75
- DSP56000 Family Manual 76
- INTERLOCKS 80
- Interlocks 80
- 6.3 STACK EXTENSION DELAYS 81
- Interlocks? 83
- COMPACT OPCODE USE 86
- Instructions 87
- Compact Opcode Use 89
- Cycle Count of an Instruction 89
- 7.2 ADDRESSING MODES 90
- 7.2.2 Short Addressing Mode 91
- 7.2.3 Short Immediate Mode 91
- 7.2.5 Register Addressing 92
- 7.2.6 Word Count 92
- 7.3 PERIPHERAL ADDRESSING 92
- 7.4 SPECIAL INSTRUCTIONS 93
- 7.4.1 Dual Data Spaces 93
- 7.4.3 Clearing Registers 94
- Special Instructions 95
- SAVING POWER 96
- A.1.2 Stop Standby Mode 97
- A.1.3 Low-Power Clock Divider 97
- Saving Power 98
- Disabling Functional Blocks 98
- DEBUG AND TEST SUPPORT 100
- B.2 JTAG PORT FEATURES 101
- B.3 ADDRESS TRACING 102
- Debug and Test Support 103
- Address Tracing 103
- USING THE PROFILER 104
- C.3 THE PROFILING REPORT 105
- C.3.1 Basic Report 105
- C.3.2 Symbol Report 106
- Using the Profiler 107
- C.3.4 Code Coverage Report 108
- C.3.5 Basic Subroutine Report 109
- C.3.8 Subroutine Call Report 111
- C.4 USING THE PROFILE REPORT 111
- How to reach us: 112
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