On the PSTART and PEND parameters, you specify the starting and ending addresses of the area to be referenced. If the reference is in a backward direction, the ending address will be smaller than the starting address.
PSTART identifies the first byte of the data area that the program references with the defined pattern; PEND identifies the last byte.
When a gap exists, define PSTART and PEND according to the following
rules:
- If direction is forward, PSTART must be the first byte (low-address end) of a reference unit; PEND can be any part of a reference unit or a gap.
- If direction is backward, PSTART must be the last byte (high-address end) of a reference unit; PEND can be any part of a reference unit or a gap.
Figure 1 illustrates a reference pattern that includes
a reference unit of 2000 bytes and a gap of 5000 bytes. When direction
is forward, PSTART must be the beginning of a reference unit. PEND
can be any part of a gap or reference unit.
Figure 1. Illustration
of Forward Direction in a Reference Pattern
Figure 2 illustrates the same reference pattern and
the same area; however, the direction is backward. Therefore, PSTART
must be the last byte of a reference unit and PEND can be any part
of a gap or reference unit.
Figure 2. Illustration
of Backward Direction in a Reference Pattern
If the data area is in a data space, use the STOKEN parameter to identify the data space. You received the STOKEN of the data space from another program or from the DSPSERV macro when you created the data space. STOKEN=0, the default, tells the system that the data is in the primary address space.