MPLAB C Compiler for PIC24 MCUs and dsPIC DSCs ... - Microchip

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16-Bit C Compiler User’s Guide 4.9 THE C STACK USAGE The C compiler uses the software stack to: • Allocate automatic variables • Pass arguments to functions • Save the processor status in interrupt functions • Save function return address • Store temporary results • Save registers across function calls The run-time stack grows upward from lower addresses to higher addresses. The compiler uses two working registers to manage the stack: • W15 – This is the Stack Pointer (SP). It points to the top of stack which is defined to be the first unused location on the stack. • W14 – This is the Frame Pointer (FP). It points to the current function’s frame. Each function, if required, creates a new frame at the top of the stack from which automatic and temporary variables are allocated. The compiler option -fomit-frame-pointer can be used to restrict the use of the FP. FIGURE 4-1: STACK AND FRAME POINTERS Stack grows toward greater addresses Function Frame SP (W15) FP (W14) The C run-time startup modules (crt0.o and crt1.o in libpic30.a) initialize the Stack Pointer W15 to point to the bottom of the stack and initialize the Stack Pointer Limit register to point to the top of the stack. The stack grows up and if it should grow beyond the value in the Stack Pointer Limit register, then a stack error trap will be taken. The user may initialize the Stack Pointer Limit register to further restrict stack growth. The following diagrams illustrate the steps involved in calling a function. Executing a CALL or RCALL instruction pushes the return address onto the software stack. See Figure 4-2. DS51284H-page 70 © 2008 Microchip Technology Inc.
FIGURE 4-2: CALL OR RCALL Stack grows toward greater addresses Run Time Environment The called function (callee) can now allocate space for its local context (Figure 4-3). FIGURE 4-3: CALLEE SPACE ALLOCATION Stack grows toward greater addresses Return addr [23:16] Return addr [15:0] Parameter 1 SP (W15) FP (W14) © 2008 Microchip Technology Inc. DS51284H-page 71 : Parameter n-1 Parameter n Caller’s Frame Local Variables and Temporaries Previous FP Return addr [23:16] Return addr [15:0] Parameter 1 : Parameter n-1 Parameter n Caller’s Frame SP (W15) FP (W14)
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MPLAB ® C COMPILER FOR PIC24 MCUs
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Table of Contents A.5 Identifiers .
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INTRODUCTION MPLAB ® C COMPILER FO
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CONVENTIONS USED IN THIS GUIDE The
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THE MICROCHIP WEB SITE Preface C Re
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1.1 INTRODUCTION 1.2 HIGHLIGHTS MPL
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1.5 COMPILER FEATURE SET Compiler O
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Differences Between 16-Bit Device C
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Page 25 and 26: Differences Between 16-Bit Device C
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Page 41 and 42: Using the Compiler on the Command L
Page 65 and 66: 3.6 ENVIRONMENT VARIABLES Using the
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Page 71 and 72: 4.5 MEMORY SPACES Run Time Environm
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Page 79 and 80: 4.11 FUNCTION CALL CONVENTIONS Run
Page 81 and 82: Run Time Environment The compiler a
Page 83 and 84: 4.14.2 String Literals as Arguments
Page 85 and 86: 5.1 INTRODUCTION 5.2 HIGHLIGHTS MPL
Page 87 and 88: 6.1 INTRODUCTION MPLAB ® C COMPILE
Page 89 and 90: 6.3 PMP POINTERS Additional C Point
Page 91 and 92: 6.4 EXTERNAL POINTERS 6.3.3 Define
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Page 95 and 96: Additional C Pointer Types } else {
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Page 101 and 102: 7.6 USING MACROS Device Support Fil
Page 103 and 104: EXAMPLE 7-2: EEDATA ACCESS VIA PSV
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Mixing Assembly Language and C Modu
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A.5 IDENTIFIERS A.6 CHARACTERS Impl
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Implementation-Defined Behavior The
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A.15 PREPROCESSING DIRECTIVES Imple
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A.17 SIGNALS A.18 STREAMS AND FILES
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A.24 GETENV A.25 SYSTEM A.26 STRERR
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B.1 INTRODUCTION MPLAB ® C COMPILE
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__builtin_btg Built-in Functions De
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__builtin_clr_prefetch Argument: xp
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__builtin_dmaoffset Built-in Functi
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__builtin_fbcl Built-in Functions A
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__builtin_modsd Argument: dividend
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__builtin_mpy Error Messages An err
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__builtin_mulss Built-in Functions
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__builtin_psvoffset Built-in Functi
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__builtin_subab Built-in Functions
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__builtin_tblwth Built-in Functions
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C.1 INTRODUCTION C.2 ERRORS MPLAB
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Diagnostics ambiguous abbreviation
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Diagnostics cast specifies function
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F Diagnostics ‘identifier’ fail
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Diagnostics initializer for static
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Diagnostics invalid use of undefine
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N Diagnostics negative width in bit
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R Diagnostics redeclaration of ‘i
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Diagnostics symbol ‘symbol’ not
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Diagnostics void expression between
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Diagnostics anonymous union declare
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Diagnostics comparison between sign
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duplicate ‘const’ The ‘const
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Diagnostics function might be possi
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Diagnostics ‘identifier’ is nar
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Diagnostics library function ‘ide
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P Diagnostics parameter has incompl
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Diagnostics shift count >= width of
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Diagnostics too many arguments for
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V Diagnostics __VA_ARGS__ can only
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MPLAB C Compiler for PIC18 MCUs vs.
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E.1 INTRODUCTION E.2 HIGHLIGHTS MPL
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G.1 PREAMBLE MPLAB ® C COMPILER FO
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G.3 VERBATIM COPYING G.4 COPYING IN
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GNU Free Documentation License incl
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Glossary File Registers On-chip dat
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Glossary Machine Language A set of
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Glossary Stack, Software Memory use
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Symbols __builtin_add..............
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-fpack-struct .....................
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-idirafter.........................
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Peephole Optimization..............
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-Wsequence-point...................
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