NetIPC 3000/XL Programmer's Reference Manual (5958-8600)

Chapter 3 63
NetIPC Intrinsics
Common Parameters
Figure 3-3 Data Location Descriptor — Vectored Data
Compatibility Mode
In compatibility mode, the data location descriptor is eight bytes long
and consists of four 2-byte fields. If the vector points to the stack, that
is, type = 0, the value you input into the Data Segment Table (DST) is
zero (DST = 0).
A compatibility mode data location descriptor consists of the following
fields:
• descriptor type (represented by a 2-byte integer); The
compatibility mode descriptor type field can have one of the
following values:
0 — (Stack) the offset is a DB-relative byte address on the calling
process’s data stack (the DST is ignored);
1 — (DST Index) DST is the logical index number returned by the
MPE XL HPGETDSEG intrinsic;
2 — (DST Number) DST is an actual data segment number. All data
segment references, that is, calls in split-stack mode, require
privileged mode.
• DST (data segment table) number or index;
• byte offset indicating the start of the data to be transmitted. (This
would be the byte count from DB on the calling process’s stack or
segment relative from the extra data segment (XDS)).
Byte
0
1
2
3
4
5
6
7
descriptor type
DST
byte offset
byte length
Byte
0
1
2
3
4
5
6
7
8
9
10
11
(64 bits)
native
mode
address
byte length
descriptor type = 4
Compatibility Mode Native Mode