Function Declarations

The C51 Compiler provides a number of extensions for standard C function declarations. These extensions allow you to:

• Declare a function as an interrupt procedure
• Choose the register bank used
• Select the memory model
• Declare a reentrant function
• Declare alien functions

You may include these extensions or attributes (many of which may be combined) in the function declaration. Use the following standard format for your C51 Compiler function declarations.

« return_type » funcname (« args ») « {small | compact | large} »
                                    « reentrant »
                                    « interrupt x »
                                    « using y »

where:

return_type	is the type of the value returned from the function. If no type is specified, int is assumed.
funcname	is the name of the function.
args	is the argument list for the function.
small	explicitly defines the function uses the small memory model.
compact	explicitly defines the function uses the compact memory model.
large	explicitly defines the function uses the large memory model.
reentrant	indicates that the function is recursive or reentrant.
interrupt	indicates that the function is an interrupt function.
x	is the interrupt number.
using	specifies which register bank the function uses.
y	is the register bank number.

Descriptions of these attributes and other features are described in detail in the following sections.