Motorola MVME2600 Series User Manual download pdf (Page 325)

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5System Calls

Introduction

This chapter describes the PPCBug System Call handler, which

allows system calls from user programs. The system calls can be

used to access selected functional routines contained within the

debugger, including input and output routines. The System Call

handler may also be used to transfer control to the debugger at the

end of a user program (refer to .RETURN on page 5-62).

In the descriptions of some input and output functions, reference is

made to the default input port or the default output port. After

power-up or reset, the default input and output port is initialized to

be port 0 (the debug port). The defaults may be changed, however,

using the .REDIR_I and .REDIR_O functions.

Invoking System Calls

The System Call handler is accessible through the SC (system call)

instruction, with exception vector $00C00 (System Call Exception).

To invoke a system call from a user program, insert the following

code into the source program. The code corresponding to the

particular system routine is specified in register R10. Parameters

are passed and returned in registers R3 to Rn, where n is less than

10.

ADDI R10,R0,$XXXX

$XXXX is the 16-bit code for the system call routine, and SC is the

system call instruction (system call to the debugger). Register R10

is set to $0000XXXX.

Refer to Chapter 4 for information on using the SYSCALL system

call instruction in the One-line Assembler.

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Motorola MVME2600 Series User Manual Page 325

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