Altera Nios II C2H Compiler Manuel d'utilisateur Page 77
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- Table des matières
- MARQUE LIVRES
Noté. / 5. Basé sur avis des utilisateurs
Altera Corporation 9.1 3–37
November 2009 Nios II C2H Compiler User Guide
C-to-Hardware Mapping Reference
Figure 3–17. Using Another Pointer to Avoid Self-Dependence
1 If a data structure is referenced by two pointers and one or more
of them is restrict-qualified, the ISO C 99 standard specifies that
the behavior is undefined. Therefore, make sure that you fully
understand the range of values that a pointer can take on during
the execution of your application before applying the
__restrict__ qualifier. Improper application can result in
undesirable functional changes to the code than cannot be
debugged in software, due to the limitations of restrict-based
optimizations in conventional compilers.
1 The ISO C 99 standard specifies that the volatile type
qualifier overrides the __restrict__ pointer type. This
means that __restrict__ has no effect on volatile
pointers. To break pointer dependencies between volatile
pointers, use separate interrupt-enabled accelerators instead of
multiple loops in the same accelerator. For details about
interrupt-enabled accelerators, see “Interrupt Pragma” on
page 6–4.
Using Physically Separate Slave Ports to Break Dependencies
If the master ports associated with two pointers do not access any shared
slave ports in the SOPC Builder system, then the C2H Compiler assumes
that the pointers do not alias. Section “Master-Slave Connections” on
page 3–23 describes how to limit the master-slave connections, which can
be an effective method to prevent aliasing.
Read Operations with Latency
Memory latency and other access delays affect how the C2H Compiler
schedules operations. Inherently, an operation cannot proceed until the
data for the operation arrives, which depends on memory latency. The
C2H Compiler generates logic within hardware accelerators to manage
- Nios II C2H Compiler 1
- User Guide 1
- UG-N2C2HCMPLR-1.6 2
- Contents 3
- Chapter 6. Pragma Reference 4
- 1. Introduction to the 7
- Target Audience 8
- Introduction 8
- Altera Corporation 9.1 1–5 11
- C2H Compiler 12
- Concepts 12
- Hardware and Software 13
- 1–8 9.1 Altera Corporation 14
- C2H Compiler Concepts 14
- System Architecture 15
- Appropriate for 19
- Hardware 19
- Acceleration 19
- Poor Acceleration Candidates 20
- Next Steps 22
- 2. Getting Started Tutorial 23
- Typical Design 24
- OpenCore Plus Evaluation 25
- Tutorial 26
- Altera Corporation 9.1 2–5 27
- Getting Started Tutorial 27
- Create the Software Project 28
- Altera Corporation 9.1 2–7 29
- 2–8 9.1 Altera Corporation 30
- Altera Corporation 9.1 2–9 31
- Rebuild the Project 32
- Remove the Accelerator 37
- 3. C-to-Hardware Mapping 41
- Reference 41
- Assignments 42
- >> 44
- << 44
- Iteration Statements 45
- Selection Statements 46
- Altera Corporation 9.1 3–7 47
- Conditional Operator ?: 48
- Altera Corporation 9.1 3–9 49
- Subfunction Calls 51
- Variable 53
- Declarations 53
- Scalar Variables 54
- Accesses 55
- Memory Accesses 58
- Volatile Type Qualifier 59
- Address Computation 61
- Data Computation 62
- Master-Slave Connections 63
- Array Subscript Operator 66
- Structure and Union Operators 68
- Scheduling 70
- Data Dependencies 71
- Pointer Aliasing 72
- int offset_b) 75
- my_ptr[offset_a] = a + 7; 75
- my_ptrb[offset_b] = b + 8; 75
- Read Operations with Latency 77
- Stalling 79
- Loop Pipelining 82
- Loop-Carried Dependencies 84
- Subfunction Pipelining 89
- Resource 91
- Resource Sharing 92
- 4. Understanding the C2H 95
- Configuration Meaning 96
- Altera Corporation 9.1 4–5 99
- 4–6 9.1 Altera Corporation 100
- Resources 100
- Altera Corporation 9.1 4–7 101
- Understanding the C2H View 101
- 4–8 9.1 Altera Corporation 102
- Altera Corporation 9.1 4–9 103
- Performance 104
- Loop Latency 105
- Scheduling Information 108
- Further Reading 113
- 5. Accelerating Code Using 115
- Tools Command Line 115
- Altera Corporation 9.1 5–3 117
- 5–4 9.1 Altera Corporation 118
- C2H Performance Metrics 118
- 6. Pragma Reference 119
- Reducing Arbitration Logic 120
- Flow Control 121
- Interrupt 122
- Unshare Pointer 123
- 6–6 9.1 Altera Corporation 124
- Unshare Pointer Pragma 124
- 7. ANSI C Compliance and 125
- Restrictions 125
- 7–2 9.1 Altera Corporation 126
- Language 126
- Expressions 127
- Functions 128
- Altera Corporation 9.1 7–5 129
- 7–6 9.1 Altera Corporation 130
- Altera Corporation 9.1 7–7 131
- Goto (Section 6.8.6.1) 132
- Other Restrictions 134
- Additional Information 135
- Revision History 136
- How to Contact 137
- Typographic 137
- Conventions 137
- Visual Cue Meaning 138
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