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

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16-Bit C Compiler User’s Guide 5.5 FLOATING POINT 5.6 POINTERS For information on implementation-defined behavior of integers, see Section A.7 “Integers”. The compiler uses the IEEE-754 format. Table 5-2 shows floating point data types are supported. TABLE 5-2: FLOATING POINT DATA TYPES Type Bits E Min E Max N Min N Max float 32 -126 127 2 -126 2 128 double* 32 -126 127 2 -126 long double 64 -1022 1023 2 -1022 E = Exponent N = Normalized (approximate) * double is equivalent to long double if -fno-short-double is used. For information on implementation-defined behavior of floating point numbers, see section Section A.8 “Floating Point”. All standard pointers are 16-bits wide. This is sufficient for full data space access (64 KB) and the small code model (32 Kwords of code.) In the large code model (>32 Kwords of code), pointers may resolve to “handles”; that is, the pointer is the address of a GOTO instruction which is located in the first 32 Kwords of program space. A set of special purpose, 32-bit data pointers are also available. See Chapter 6. “Additional C Pointer Types” for more information. DS51284H-page 80 © 2008 Microchip Technology Inc. 2 128 2 1024
6.1 INTRODUCTION MPLAB ® C COMPILER FOR PIC24 MCUs AND dsPIC ® DSCs USER’S GUIDE Chapter 6. Additional C Pointer Types MPLAB C Compiler for PIC24 MCUs and dsPIC ® DSCs (formerly MPLAB C30) offers some extended pointer modes to help access more of the unique features of Microchip’s 16-bit product architecture. Extended pointers and their use will be covered in this chapter. • Managed PSV Pointers - for reading more data through the PSV • PMP Pointers - for accessing data via the PMP peripheral (where available) • External Pointers - for accessing external memory in a user-defined fashion Although the concentration will be on pointer access, defining variables and ensuring that the data is allocated in the correct region of the 16-bit architectures (bi-polar) memory is also covered. This chapter will make use of concepts introduced in Chapter 2. “Differences Between 16-Bit Device C and ANSI C”. 6.2 MANAGED PSV POINTERS The dsPIC30F/33F and PIC24F/H families of processors contain hardware support for accessing data from within program Flash using a hardware feature that is commonly called Program Space Visibility (PSV). More detail about how PSV works can be found in device data sheets or family reference manuals. Also, see Section 4.14 “Program Space Visibility (PSV) Usage” and Section 8.10 “PSV Usage with Interrupt Service Routines”. Briefly, the architecture allows the mapping of one 32K page of Flash into the upper 32K of the data address space via the Special Function Register (SFR) PSVPAG. By default the compiler only supports direct access to one single PSV page, referred to as the auto_psv space. In this model, 16-bit data pointers can be used. However, on larger devices, this can make it difficult to manage large amounts of constant data stored in Flash. The extensions presented here allow the definition of a variable as being a ‘managed’ PSV variable. This means that the compiler will manipulate both the offset (within a PSV page) and the page itself. As a consequence, data pointers must be 32 bits. The compiler will probably generate more instructions than the single PSV page model, but that is the price being paid to buy more flexibility and shorter coding time to access larger amounts of data in Flash. 6.2.1 Defining Data for Managed PSV Access Chapter 2. “Differences Between 16-Bit Device C and ANSI C” introduces C extensions which allows the identification of extra information for a variable or function. The compiler provides the space attribute to help place variables into different areas (spaces) of memory. © 2008 Microchip Technology Inc. DS51284H-page 81
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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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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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Peephole Optimization..............
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-Wsequence-point...................
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