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

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16-Bit C Compiler User’s Guide 4.4 STARTUP AND INITIALIZATION Two C run-time startup modules are included in the libpic30.a archive/library. The entry point for both startup modules is __reset. The linker scripts construct a GOTO __reset instruction at location 0 in program memory, which transfers control upon device reset. The primary startup module (crt0.o) is linked by default and performs the following: 1. The Stack Pointer (W15) and Stack Pointer Limit register (SPLIM) are initialized, using values provided by the linker or a custom linker script. For more information, see Section 4.8 “Software Stack”. 2. If a .const section is defined, it is mapped into the program space visibility window by initializing the PSVPAG and CORCON registers. Note that a .const section is defined when the “Constants in code space” option is selected in MPLAB IDE, or the default -mconst-in-code option is specified on the compiler command line. 3. The data initialization template in section .dinit is read, causing all uninitialized sections to be cleared, and all initialized sections to be initialized with values read from program memory. The data initialization template is created by the linker, and supports the standard sections listed in Section 4.3 “Address Spaces”, as well as the user-defined sections. Note: The persistent data section .pbss is never cleared or initialized. 4. If the application has defined user_init functions, these are invoked. The order of execution depends on link order. 5. The function main is called with no parameters. 6. If main returns, the processor will reset. The alternate startup module (crt1.o) is linked when the -Wl, --no-data-init option is specified. It performs the same operations, except for step (3), which is omitted. The alternate startup module is smaller than the primary module, and can be selected to conserve program memory if data initialization is not required. Source code (in dsPIC DSC assembly language) for both modules is provided in the c:\Program Files\Microchip\MPLAB C30\src directory. The startup modules may be modified if necessary. For example, if an application requires main to be called with parameters, a conditional assembly directive may be changed to provide this support. DS51284H-page 64 © 2008 Microchip Technology Inc.
4.5 MEMORY SPACES Run Time Environment Static and external variables are normally allocated in general purpose data memory. Const-qualified variables will be allocated in general purpose data memory if the constants-in-data memory model is selected, or in program memory if the constants-in-code memory model is selected. The compiler defines several special purpose memory spaces to match architectural features of 16-bit devices. Static and external variables may be allocated in the special purpose memory spaces through use of the space attribute, described in Section 2.3.1 “Specifying Attributes of Variables”: data General data space. Variables in general data space can be accessed using ordinary C statements. This is the default allocation. xmemory - dsPIC30F/dsPIC33F devices only X data address space. Variables in X data space can be accessed using ordinary C statements. X data address space has special relevance for DSP-oriented libraries and/or assembly language instructions. ymemory - dsPIC30F/dsPIC33F devices only Y data address space. Variables in Y data space can be accessed using ordinary C statements. Y data address space has special relevance for DSP-oriented libraries and/or assembly language instructions. prog General program space, which is normally reserved for executable code. Variables in program space can not be accessed using ordinary C statements. They must be explicitly accessed by the programmer, usually using table-access inline assembly instructions, or using the program space visibility window. auto_psv A compiler-managed area in program space, designated for program space visibility window access. Variables in this space can be read (but not written) using ordinary C statements and are subject to a maximum of 32K total space allocated. psv Program space, designated for program space visibility window access. Variables in PSV space are not managed by the compiler and can not be accessed using ordinary C statements. They must be explicitly accessed by the programmer, usually using table-access inline assembly instructions, or using the program space visibility window. Variables in PSV space can be accessed using a single setting of the PSVPAG register. eedata - dsPIC30F/dsPIC33F devices only Data EEPROM space, a region of 16-bit wide non-volatile memory located at high addresses in program memory. Variables in eedata space can not be accessed using ordinary C statements. They must be explicitly accessed by the programmer, usually using table-access inline assembly instructions, or using the program space visibility window. dma - PIC24H MCUs, dsPIC33F DSCs only DMA memory. Variables in DMA memory can be accessed using ordinary C statements and by the DMA peripheral. © 2008 Microchip Technology Inc. DS51284H-page 65
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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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Page 19 and 20: Differences Between 16-Bit Device C
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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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Interrupts 2. Unsafe: read bar inte
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LATGbits.LATG2 = 0; /* No problem l
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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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