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

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16-Bit C Compiler User’s Guide ordering, so these functions cannot rely on other user_init functions having been previously run; these functions will be called after PSV and data initialization. A user_init may still be called by the executing program. For example: void __attribute__((user_init)) initialize_me(void) { // perform initalization sequence alpha alpha beta } weak See Section 2.3.1 “Specifying Attributes of Variables” for information on the weak attribute. 2.3.3 Inline Functions By declaring a function inline, you can direct the compiler to integrate that function’s code into the code for its callers. This usually makes execution faster by eliminating the function-call overhead. In addition, if any of the actual argument values are constant, their known values may permit simplifications at compile time, so that not all of the inline function’s code needs to be included. The effect on code size is less predictable. Machine code may be larger or smaller with inline functions, depending on the particular case. Note: Function inlining will only take place when the function’s definition is visible (not just the prototype). In order to have a function inlined into more than one source file, the function definition may be placed into a header file that is included by each of the source files. To declare a function inline, use the inline keyword in its declaration, like this: inline int inc (int *a) { (*a)++; } (If you are using the -traditional option or the -ansi option, write __inline__ instead of inline.) You can also make all “simple enough” functions inline with the command-line option -finline-functions. The compiler heuristically decides which functions are simple enough to be worth integrating in this way, based on an estimate of the function’s size. Note: The inline keyword will only be recognized with -finline or optimizations enabled. Certain usages in a function definition can make it unsuitable for inline substitution. Among these usages are: use of varargs, use of alloca, use of variable-sized data, use of computed goto and use of nonlocal goto. Using the command-line option -Winline will warn when a function marked inline could not be substituted, and will give the reason for the failure. In compiler syntax, the inline keyword does not affect the linkage of the function. When a function is both inline and static, if all calls to the function are integrated into the caller and the function’s address is never used, then the function’s own assembler code is never referenced. In this case, the compiler does not actually output assembler code for the function, unless you specify the command-line option -fkeep-inline-functions. Some calls cannot be integrated for various reasons (in particular, calls that precede the function’s definition cannot be integrated and neither can recursive calls within the definition). If there is a nonintegrated call, then the function is compiled to assembler code as usual. The function must also be compiled DS51284H-page 26 © 2008 Microchip Technology Inc.
Differences Between 16-Bit Device C and ANSI C as usual if the program refers to its address, because that can’t be inlined. The compiler will only eliminate inline functions if they are declared to be static and if the function definition precedes all uses of the function. When an inline function is not static, then the compiler must assume that there may be calls from other source files. Since a global symbol can be defined only once in any program, the function must not be defined in the other source files, so the calls therein cannot be integrated. Therefore, a non-static inline function is always compiled on its own in the usual fashion. If you specify both inline and extern in the function definition, then the definition is used only for inlining. In no case is the function compiled on its own, not even if you refer to its address explicitly. Such an address becomes an external reference, as if you had only declared the function and had not defined it. This combination of inline and extern has a similar effect to a macro. Put a function definition in a header file with these keywords and put another copy of the definition (lacking inline and extern) in a library file. The definition in the header file will cause most calls to the function to be inlined. If any uses of the function remain, they will refer to the single copy in the library. 2.3.4 Variables in Specified Registers The compiler allows you to put a few global variables into specified hardware registers. Note: Using too many registers, in particular register W0, may impair the ability of the 16-bit compiler to compile. You can also specify the register in which an ordinary register variable should be allocated. • Global register variables reserve registers throughout the program. This may be useful in programs such as programming language interpreters which have a couple of global variables that are accessed very often. • Local register variables in specific registers do not reserve the registers. The compiler’s data flow analysis is capable of determining where the specified registers contain live values, and where they are available for other uses. Stores into local register variables may be deleted when they appear to be unused. References to local register variables may be deleted, moved or simplified. These local variables are sometimes convenient for use with the extended inline assembly (see Chapter 9. “Mixing Assembly Language and C Modules”), if you want to write one output of the assembler instruction directly into a particular register. (This will work provided the register you specify fits the constraints specified for that operand in the inline assembly statement). 2.3.4.1 DEFINING GLOBAL REGISTER VARIABLES You can define a global register variable like this: register int *foo asm ("w8"); Here w8 is the name of the register which should be used. Choose a register that is normally saved and restored by function calls (W8-W13), so that library routines will not clobber it. Defining a global register variable in a certain register reserves that register entirely for this use, at least within the current compilation. The register will not be allocated for any other purpose in the functions in the current compilation. The register will not be saved and restored by these functions. Stores into this register are never deleted even if they would appear to be dead, but references may be deleted, moved or simplified. © 2008 Microchip Technology Inc. DS51284H-page 27
Page 1 and 2: MPLAB ® C COMPILER FOR PIC24 MCUs
Page 5 and 6: Table of Contents A.5 Identifiers .
Page 7 and 8: INTRODUCTION MPLAB ® C COMPILER FO
Page 9 and 10: CONVENTIONS USED IN THIS GUIDE The
Page 11 and 12: THE MICROCHIP WEB SITE Preface C Re
Page 13 and 14: 1.1 INTRODUCTION 1.2 HIGHLIGHTS MPL
Page 15 and 16: 1.5 COMPILER FEATURE SET Compiler O
Page 19 and 20: Differences Between 16-Bit Device C
Page 31: Differences Between 16-Bit Device C
Page 41 and 42: Using the Compiler on the Command L
Page 65 and 66: 3.6 ENVIRONMENT VARIABLES Using the
Page 69 and 70: 4.1 INTRODUCTION 4.2 HIGHLIGHTS 4.3
Page 71 and 72: 4.5 MEMORY SPACES Run Time Environm
Page 73 and 74: Run Time Environment 1. It is possi
Page 75 and 76: 4.8 SOFTWARE STACK Run Time Environ
Page 77 and 78: FIGURE 4-2: CALL OR RCALL Stack gro
Page 79 and 80: 4.11 FUNCTION CALL CONVENTIONS Run
Page 81 and 82: Run Time Environment The compiler a
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4.14.2 String Literals as Arguments
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5.1 INTRODUCTION 5.2 HIGHLIGHTS MPL
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6.1 INTRODUCTION MPLAB ® C COMPILE
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6.3 PMP POINTERS Additional C Point
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6.4 EXTERNAL POINTERS 6.3.3 Define
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ead_external16 Additional C Pointer
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Additional C Pointer Types } else {
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7.5 USING SFRS Device Support Files
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7.6 USING MACROS Device Support Fil
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EXAMPLE 7-2: EEDATA ACCESS VIA PSV
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Interrupts When using the interrupt
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8.4.1 dsPIC30F DSCs (Non-SMPS) Inte
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8.4.3 PIC24F MCUs Interrupt Vectors
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Interrupts TABLE 8-3: INTERRUPT VEC
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Interrupts TABLE 8-4: INTERRUPT VEC
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85 _Interrupt85 _AltInterrupt85 Res
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8.8 ENABLING/DISABLING INTERRUPTS I
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Interrupts 2. Unsafe: read bar inte
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LATGbits.LATG2 = 0; /* No problem l
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MPLAB ® C COMPILER FOR PIC24 MCUs
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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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MPLAB C Compiler for PIC24 MCUs and dsPIC DSCs ... - Microchip

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