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

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16-Bit C Compiler User’s Guide D.18 OPTIMIZATIONS The following optimizations are part of each compiler. D.19 OBJECT MODULE FORMAT The MPLAB C Compiler for PIC18 MCUs and the MPLAB C Compiler for PIC24 MCUs and dsPIC ® DSCs use different COFF File Formats that are not interchangeable. D.20 IMPLEMENTATION-DEFINED BEHAVIOR MPLAB ® C Compiler for PIC18 MCUs 16-Bit Devices Branches(-Ob+) Optimization settings (-On where n is 1, 2, 3 or s) Code Straightening(-Os+) Tail Merging(-Ot+) Unreachable Code Removal(-Ou+) Copy Propagation(-Op+) Redundant Store Removal(-Or+) Dead Code Removal(-Od+) (1) Duplicate String Merging (-Om+) -fwritable-strings Banking (-On+) N/A – Banking not used WREG Content Tracking(-Ow+) All registers are automatically tracked Procedural Abstraction(-Opa+) Procedural Abstraction(-mpa) Note 1: These optimization settings will satisfy most needs. Additional flags may be used for “fine-tuning". See Section 3.5.6 “Options for Controlling Optimization” for more information. For the right-shift of a negative-signed integral value: • The PIC18 MCU Compiler does not retain the sign bit • The 16-Bit Device Compiler retains the sign bit DS51284H-page 208 © 2008 Microchip Technology Inc.
MPLAB C Compiler for PIC18 MCUs vs. 16-Bit Devices D.21 BIT FIELDS Bit fields in the PIC18 MCU Compiler cannot cross byte storage boundaries and, therefore, cannot be greater than 8 bits in size. The 16-Bit Device Compiler supports bit fields with any bit size, up to the size of the underlying type. Any integral type can be made into a bit field. The allocation cannot cross a bit boundary natural to the underlying type. For example: struct foo { long long i:40; int j:16; char k:8; } x; struct bar { long long I:40; char J:8; int K:16; } y; struct foo will have a size of 10 bytes using the 16-Bit Device Compiler. i will be allocated at bit offset 0 (through 39). There will be 8 bits of padding before j, allocated at bit offset 48. If j were allocated at the next available bit offset, 40, it would cross a storage boundary for a 16 bit integer. k will be allocated after j, at bit offset 64. The structure will contain 8 bits of padding at the end to maintain the required alignment in the case of an array. The alignment is 2 bytes because the largest alignment in the structure is 2 bytes. struct bar will have a size of 8 bytes using the 16-Bit Device Compiler. I will be allocated at bit offset 0 (through 39). There is no need to pad before J because it will not cross a storage boundary for a char. J is allocated at bit offset 40. K can be allocated starting at bit offset 48, completing the structure without wasting any space. © 2008 Microchip Technology Inc. DS51284H-page 209
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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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Using the Compiler on the Command L
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3.6 ENVIRONMENT VARIABLES Using the
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4.1 INTRODUCTION 4.2 HIGHLIGHTS 4.3
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4.5 MEMORY SPACES Run Time Environm
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Run Time Environment 1. It is possi
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4.8 SOFTWARE STACK Run Time Environ
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FIGURE 4-2: CALL OR RCALL Stack gro
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4.11 FUNCTION CALL CONVENTIONS Run
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Run Time Environment The compiler a
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4.14.2 String Literals as Arguments
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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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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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Page 169 and 170: C.1 INTRODUCTION C.2 ERRORS MPLAB
Page 171 and 172: Diagnostics ambiguous abbreviation
Page 173 and 174: Diagnostics cast specifies function
Page 175 and 176: F Diagnostics ‘identifier’ fail
Page 177 and 178: Diagnostics initializer for static
Page 179 and 180: Diagnostics invalid use of undefine
Page 181 and 182: N Diagnostics negative width in bit
Page 183 and 184: R Diagnostics redeclaration of ‘i
Page 185 and 186: Diagnostics symbol ‘symbol’ not
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Page 189 and 190: Diagnostics anonymous union declare
Page 191 and 192: Diagnostics comparison between sign
Page 193 and 194: duplicate ‘const’ The ‘const
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Page 201 and 202: P Diagnostics parameter has incompl
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Page 217 and 218: E.1 INTRODUCTION E.2 HIGHLIGHTS MPL
Page 221 and 222: G.1 PREAMBLE MPLAB ® C COMPILER FO
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Page 229 and 230: Glossary File Registers On-chip dat
Page 231 and 232: Glossary Machine Language A set of
Page 233 and 234: Glossary Stack, Software Memory use
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Page 237 and 238: -fpack-struct .....................
Page 239 and 240: -idirafter.........................
Page 241 and 242: Peephole Optimization..............
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