Asynchronous Serial Communications Programmer's Reference Manual (32022-90052)

50 Chapter2

Controlling Asynchronous Devices Programmatically

MPE/iX System Intrinsics

Other Types of Intrinsics

The discussion in this manual pertains exclusively to system intrinsics.

Certain application programs and system utilities also provide

subroutines that are referred to as intrinsics. For example,

VPLUS/3000 iX provides a set of intrinsics for handling page block

mode programming. For a description of VPLUS/3000 iX intrinsics see

the VPLUS Reference Manual. For descriptions of intrinsics provided

by any other application or utility, see the documentation for that

program.

Using Intrinsics in your Program

You can call any system intrinsic from any supported language, but the

details of the calling procedure vary according to the language being

used. In general, you should follow the steps as summarized:

1. Refer to the intrinsic description in Chapter 8, “Intrinsics

Reference,” to determine the parameter types and their positions in

the parameter list.

2. Declare variables to be passed as parameters, using types

appropriate to the language you are using to write your program.

3. Include the name of the intrinsic in a declaration statement, if

appropriate for your programming language.

4. Issue the intrinsic call at the appropriate place in your program.

Depending on the intrinsic call, error checking is provided either

through condition codes or through a special status parameter. Because

the condition code or status return value can provide you with useful

information about what happened during execution of an intrinsic, you

should routinely check for error conditions at the completion of each

intrinsic call.

Condition Codes

Most of the intrinsics discussed in this manual use condition codes for

error checking. Condition codes are status ﬂags stored in two bits of the

status register. Their values and general meanings are shown in Table

2-1. Because the condition code status ﬂags are affected by almost every

instruction, you should check condition codes immediately after

execution of an intrinsic to make sure that the information being

returned pertains to the intrinsic and not to some subsequent activity.

The method of accessing condition codes is language speciﬁc. Pascal/iX,

for example, provides the function ccode, which returns the value 0, 1,

or 2, depending on the current condition code stored in the status

determine how to access condition code information.