VHDL Programming

Subprograms and Packages 129

MEMORY

CPU

IO_PORT

DISK_CONTROL

XBUS

Figure 5-6
Block Diagram of
Computer.

END RECORD;

TYPE xtypevector IS ARRAY( natural RANGE <>) OF xtype;

CONSTANT notdriven : xtype := (-1,-1);

FUNCTION cresolve( t : xtypevector) RETURN xtype;

END composite_res;

PACKAGE BODY composite_res IS

FUNCTION cresolve( t : xtypevector) RETURN xtype IS

VARIABLE result : xtype := notdriven;

VARIABLE drive_count : INTEGER := 0;

BEGIN

IF t’LENGTH = 0 THEN RETURN notdriven;

END IF;

FOR i IN t’RANGE LOOP

IF t(i) /= notdriven THEN

drive_count := drive_count + 1;

IF drive_count = 1 THEN

result := t(i);

ELSE

result := notdriven;

ASSERT FALSE

REPORT “multiple drivers detected”

SEVERITY ERROR;

END IF;

END IF;

END LOOP;

RETURN result;