pTAL Reference Manual (H06.08+)

Pointers
HP pTAL Reference Manual—523746-006
10-5
Structure
Structure
When you declare a VOLATILE structure pointer, the compiler generates code that
maintains the value of the pointer in memory, not in a register. Each reference to a
VOLATILE data item causes the data item to be read or written to memory even when
code is optimized. Based on the order of reads and writes in the source code,
VOLATILE also causes that precise order of memory references to be preserved,
again, when code is optimized.
You must specify the VOLATILE attribute on each field that you want to be volatile.
Address Types
pTAL address types control the addresses you store into pointers. A 32-bit address can
reference data anywhere in memory with optimal performance. The hardware does not
require programs to specify an addressing type or memory storage area.
The compiler determines the address type of a pointer from the pointer declaration.
You cannot explicitly declare a pointer’s address type.
Address types are used primarily to describe the addresses that you assign to a
pointer, not the data your program is processing.
Only operations that are meaningful for addresses are valid on address types.
Example 10-2. Declaring VOLATILE Structure Pointers
INT i;
STRUCT s;
BEGIN
INT m; ! Field m is never treated as volatile
VOLATILE INT n; ! Field n is always treated as volatile
END;
VOLATILE INT .s1(s) := @s;
INT .s2(s) := @s;
i := s1.m; ! Value of pointer s1 is read from memory on
! every reference, but value of field s1.m
! might be maintained in a register
i := s1.n; ! Value of pointer s1 is read from memory on
! every reference, as is value of s1.n
! because field n specifies VOLATILE
i := s2.n; ! Value of pointer s2 might or might not be
! from memory, but having read the pointer,
! the field s2.n is always read from memory