Specifications

40 Software Interface
The flag field contains four flags (bits 0 through 3). The rest of the bits
in the field must be 0 or the result is undefined. The sender can change
any flag in the field, except the LIR flag. The receiver can only change the
OWN flag. Table 3-4 describes each flag.
Table 3–4 Flag Field Flags
Flag
Name Bit Function
OWN 0 This flag indicates the current owner of the buffer.
If the flag is 0, the sender owns the buffer. If
the flag is 1, the receiver owns the buffer. On
initialization, the OWN flag in each buffer is set to
0.
FIB 1 This flag indicates that the buffer is the first in
a block of data. The sender sets or clears this bit
as required. This flag cannot be changed by the
receiver.
LIB 2 This flag indicates that the buffer is the last in a
block of data. The sender sets or clears this bit
as required. This flag cannot be changed by the
receiver.
LIR 3 This flag indicates that the buffer is the last in the
ring. This flag must always be valid. Senders and
receivers should be sure not to invalidate this flag
while changing the other flags.
Size
The size field indicates the exact size (in bytes) of the data section of the
buffer. The address of the next flag word in the next buffer is equal to
the value in the size field plus the address of the first data word in the
current buffer. However, if the current buffer is flagged by LIR as the
last in the ring, then a wraparound operation is needed. After module
initialization, the size field becomes a read-only field.
Used
The used field indicates the size of the used portion of the data buffer.
The sender sets this field before ownership of the buffer is given to the
receiver.