CC78K4 datasheet(159/523 Pages) NEC

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CHAPTER 10 LIBRARY FUNCTIONS

User’s Manual U15556EJ1V0UM

159

10.1 Interface Between Functions

To use a library function, the function must be called. Calling a library function is carried out by a call instruction.

The arguments and return value of a function are passed via a stack and a register, respectively. However, when the

old function interface supporting option (-ZO) is not specified, the first argument is, if possible, also passed via a

For the -ZO option, refer to CHAPTER 5 COMPILER OPTION in the CC78K4 C Compiler Operation User's

Manual (U15557E).

10.1.1 Arguments

Placing or removing arguments on or from the stack is performed by the caller (calling function). The callee

(called function) only references the argument values. However, when the argument is passed via a register, the

callee directly refers to the register and copies the value of the argument to another register, if necessary. Also,

when specifying the function call interface automatic pascal function option -ZR, removal of arguments from the stack

is performed by the called side if the argument is passed by the stack.

Arguments are placed on the stack one by one in descending order from bottom to top if the argument is passed

via the stack.

The minimum unit of data that can be stacked is 16 bits. A data type larger than 16 bits is stacked in units of 16

bits one by one from its MSB. An 8-bit type data is extended to a 16-bit type data for stacking.

When it is a large model and the argument is the address value or when it is a medium model and the argument is

the address value of the function, the argument is stacked in 3-byte units.

The following shows the list of the passing of the first argument. The second and subsequent arguments are

passed via a stack.

The function interface (passing of argument and storing of return value) of the standard library is the same as that

of normal function.

Table 10-1. List of Passing First Argument

Type of First Argument

Passing Method (Without -ZO Specification)

Passing Method

(with -ZO Specification)

1-byte, 2-byte integer

Passed via a stack

3-byte integer

WHL, small model: stack passing

Passed via a stack

4-byte integer

AX, RP2

Passed via a stack

Floating-point number

(float type)

AX, RP2

Passed via a stack

Floating-point number

(double type)

AX, RP2

Passed via a stack

Other

Passed via a stack

Remark

Of the types shown above, 1- to 4-byte integers include structures and unions.

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