6.6.3 xc16-gcc (16-bit C Compiler)

Although the MPLAB XC16 C Compiler works with MPLAB X IDE, it must be acquired separately. The full version may be purchased, or a student (limited-feature) version may be downloaded for free. See the Microchip website (www.microchip.com) for details.

A subset of command-line options may be specified in MPLAB X IDE. Select a category and then set up compiler options. For additional options, see the Driver Option Descriptions.

See also Options Page Features.

Table 6-4. General Category
Option	Description	Command Line
Generate debugging info	Create a COFF or ELF file with information to allow debugging of code in MPLAB X IDE. Note: COFF supports debugging in the `.text` section only.	`-g`
Isolate each function in a section	Check to place each function into its own section in the output file. The name of the function determines the section’s name in the output file. Note: When you specify this option, the assembler and linker may create larger object and executable files and will also be slower. Uncheck to place multiple functions in a section.	`-ffunction-sections`
Place data into its own section	Place each data item into its own section in the output file. The name of the data item determines the name of the section. When you specify this option, the assembler and linker may create larger object and executable files and will also be slower.	`-fdata-sections`
Use 64-bit double	Use `long double` instead of `double` type equivalent to float. Mixing this option across modules can have unexpected results if modules share double data either directly through argument passage or indirectly through shared buffer space	`-fno-short-double`
Fill upper value for data in flash	Fill upper flash memory with the value specified.	`-mfillupper=value`
Name the text section	Place text (program code) in a section named `name` rather than the default`.text`section.	`-mtext=name`

Table 6-5. Memory Model Category
Option	Description	Command Line
Code model	Select a code (program memory/ROM) model. - default - large (>32 K words) - small (<32 K words)	`-msmall-code` `-mlarge-code` `-msmall-code`
Data model	Select a data (data memory/RAM) model. - default - large (device dependent¹) - small (device dependent¹)	device dependant² `-mlarge-data` `-msmall-scalar`
Scalar model	Select a scalar model. - default - large (device dependent¹) - small (device dependent¹)	`-msmall-scalar` `-mlarge-scalar` `-msmall-scalar`
Location of constant model	Select a memory location for constants. - default - Data - Code	`-mconst-in-code` `-mconst-in-data` `-mconst-in-code`
Place all code in auxiliary flash	Place all code from the current translation unit into auxiliary Flash. This option is only available on devices that have auxiliary Flash.	`-mauxflash`
Put constants into auxiliary flash	When combined with -mconst-in-code, put constants into auxiliary Flash.	`-mconst-in-auxflash`
Allow arrays larger than 32K	Allow arrays that are larger than 32K, regardless of memory model.	`-menable-large-arrays`
Aggregate data model	Use aggregate data model.	`-mlarge-aggregate`
Note: For most devices 6K of RAM is the near data space, but for some devices it is 4K of RAM. For devices that have all of their data memory in the near space, the memory model is "small data" "smallscalar" so that all memory will be allocated in the near space. For all other devices the default memory model is "large data" "small scalar". This will have the effect ofallowing the tool chain to place aggregate objects, such as arrays and structure, into the far memory space. This can be over-ridden by explicitly selecting "small data" in the compiler options.

Table 6-6. OPTIMIZATION CATEGORY
Option	Description	Command Line
Optimization Level	Select an optimization level. Equivalent to `-On` option, where `n` is an option. See Options for Controlling Optimization. Your compiler license may support only some optimizations. See Chapter 18. “Optimizations.”	`-On`
Unroll loops	Check to perform the optimization of loop unrolling. This is only done for loops whose number of iterations can be determined at compile time or run time. Uncheck to not unroll loops.	`-funroll-loops`
Omit frame pointer	Check to not keep the Frame Pointer in a register for functions that don’t need one. Uncheck to keep the Frame Pointer.	`-fomit-frame-pointer`
Unlimited procedural abstraction	Enable the procedure abstraction optimization. There is no limit on the nesting level.	`-mpa`
Procedural abstraction	Enable the procedure abstraction optimization up to level `n`. Equivalent to `-mpa=n` option, where `n` equals: 0 - Optimization is disabled. 1 - The first level of abstraction is allowed; that is, instruction sequences in the source code may be abstracted into a subroutine. 2 or greater - A second level of abstraction is allowed; that is, instructions that were put into a subroutine in the first level may be abstracted into a subroutine one level deeper. This pattern continues for larger values of `n`. The net effect is to limit the subroutine call nesting depth to a maximum of `n`.	`-mpa=n`
Align arrays	Set the minimum alignment for array variables to be the largest power of two less than or equal to their total storage size, or the biggest alignment used on the machine, whichever is smaller.	`-falign-arrays`

Table 6-7. Preprocessing and Messages Category
Option	Description	Command Line
Include C dirs	Add the directory `dir` to the head of the list of directories to be searched for header files. For more information, see Additional Search Paths and Directories	`-I"dir"`
Define C macros	Define macro `macro` with the string 1 as its definition.	`-Dmacro`
ANSI-std C support	Check to support all (and only) ASCI C programs. Uncheck to support ASCI and non-ASCI programs.	`-ansi`
Use CCI syntax	Check if your code is written per the Common C Interface (CCI) syntax (see Chapter 2. “Common C Interface.”). Uncheck if you are not.	`-mcci`
Use IAR syntax	Check if your code is written per the Embedded Compiler Compatibility Mode syntax for IAR (see Appendix B. “Embedded Compiler Compatibility Mode”). Uncheck if you are not.	`-mext=IAR`
Errata	This option enables specific errata work-arounds identified by ID. Valid values for ID change from time to time and may not be required for a particular variant. The ID `all` will enable all currently supported errata work-arounds. The ID `list` will display the currently supported errata identifiers along with a brief description of the errata.	`-merrata=id`
Smart IO forwarding level	This option attempts to statically analyze format strings passed to printf, scanf and the ‘f’ and ‘v’ variations of these functions. Uses of nonfloating point format arguments will be converted to use an integer-only variation of the library functions. Equivalent to`-msmart-io=n` option where `n` equals: 0 - disables this option. 1 - only convert the literal values it can prove. 2 - causes the compiler to be optimistic and convert function calls with variable or unknown format arguments.	`-msmart-io=n`
Smart IO format strings	Specifies what the format arguments are when the compiler is unable to determine them.
Make warnings into errors	Check to halt compilation based on warnings as well as errors. Uncheck to halt compilation based on errors only.	`-Werror`
Additional warnings	Check to enable all warnings. Uncheck to disable warnings.	`-Wall`
Strict ANSI warnings	Check to issue all warnings demanded by strict ANSI C. Uncheck to issue all warnings.	`-pedantic`
Disable ISR warn	Disable warning for inappropriate use of ISR function names. By default the compiler will produce a warning if the `interrupt` is not attached to a recognized interrupt vector name. This option will disable that feature.	`-mno-isr-warn`
Enable SFR warnings	Enable warnings related to SFRs.	`-msfr-warn=on\|off`