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

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16-Bit C Compiler User’s Guide EXAMPLE 4-2: FUNCTION CALL MODEL, PASSING STRUCTURES typedef struct bar { int i; double d; } bar; void params1(int i, bar b) { /* ** W0 i ** W1 b.i ** W5:W2 b.d */ } Parameters corresponding to the ellipses (...) of a variable-length argument list are not allocated to registers. Any parameter not allocated to registers is pushed onto the stack, in right-to-left order. In the next example, the structure parameter cannot be placed in registers because it is too large. However, this does not prevent the next parameter from using a register spot. EXAMPLE 4-3: FUNCTION CALL MODEL, STACK BASED ARGUMENTS typedef struct bar { double d,e; } bar; void params2(int i, bar b, int j) { /* ** W0 i ** stack b ** W1 j */ } Accessing arguments that have been placed onto the stack depends upon whether or not a Frame Pointer has been created. Generally the compiler will produce a Frame Pointer (unless otherwise told not to do so), and stack-based parameters will be accessed via the Frame Pointer register (W14). The above example, b will be accessed from W14-22. The Frame Pointer offset of negative 22 has been calculated (refer to Figure 4-4) by removing 2 bytes for the previous FP, 4 bytes for the return address, followed by 16 bytes for b. When no Frame Pointer is used, the assembly programmer must know how much stack space has been used since entry to the procedure. If no further stack space is used, the calculation is similar to the above. b would be accessed via W15-20; 4 bytes for the return address and 16 bytes to access the start of b. 4.11.2 Return Value Function return values are returned in W0 for 8- or 16-bit scalars, W1:W0 for 32-bit scalars, and W3:W2:W1:W0 for 64-bit scalars. Aggregates are returned indirectly through W0, which is set up by the function caller to contain the address of the aggregate value. 4.11.3 Preserving Registers Across Function Calls DS51284H-page 74 © 2008 Microchip Technology Inc.
Run Time Environment The compiler arranges for registers W8-W15 to be preserved across ordinary function calls. Registers W0-W7 are available as scratch registers. For interrupt functions, the compiler arranges for all necessary registers to be preserved, namely W0-W15 and RCOUNT. 4.12 REGISTER CONVENTIONS Specific registers play specific roles in the C run-time environment. Register variables use one or more working registers, as shown in Table 4-3. TABLE 4-3: REGISTER CONVENTIONS Variable Working Register char, signed char, unsigned char W0-W13, and W14 if not used as a Frame Pointer. short, signed short, unsigned W0-W13, and W14 if not used as a Frame short Pointer. int, signed int,unsigned int W0-W13, and W14 if not used as a Frame Pointer. void * (or any pointer) W0-W13, and W14 if not used as a Frame Pointer. long, signed long, unsigned long A pair of contiguous registers, the first of which is a register from the set {W0, W2, W4, W6, W8, W10, W12}. The lower-numbered register contains the least significant 16-bits of the value. long long, signed long long, A quadruplet of contiguous registers, the first of unsigned long long which is a register from the set {W0, W4, W8}. The lower-numbered register contains the least significant 16-bits of the value. Successively higher-numbered registers contain successively more significant bits. float A pair of contiguous registers, the first of which is a register from the set {W0, W2, W4, W6, W8, W10, W12}. The lower-numbered register contains the least significant 16-bits of the significant. double* A pair of contiguous registers, the first of which is a register from the set {W0, W2, W4, W6, W8, W10, W12}. The lower-numbered register contains the least significant 16-bits of the significant. long double A quadruplet of contiguous registers, the first of which is a register from the set {W0, W4, W8}. The lower-numbered register contains the least significant 16-bits of the significant. structure 1 contiguous register per 2 bytes in the structure. * double is equivalent to long double if -fno-short-double is used. © 2008 Microchip Technology Inc. DS51284H-page 75
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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 29 and 30: 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 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
Page 93 and 94: ead_external16 Additional C Pointer
Page 95 and 96: Additional C Pointer Types } else {
Page 99 and 100: 7.5 USING SFRS Device Support Files
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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Page 111 and 112: 8.4.3 PIC24F MCUs Interrupt Vectors
Page 113 and 114: Interrupts TABLE 8-3: INTERRUPT VEC
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Page 117 and 118: 85 _Interrupt85 _AltInterrupt85 Res
Page 119 and 120: 8.8 ENABLING/DISABLING INTERRUPTS I
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Mixing Assembly Language and C Modu
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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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