Chapter 5
Issuing BlockTransfer Commands
5-6
The host application issues a
Host BT Read
command when it wants to
initiate a block transfer from an adapter. To match the response to the
request on completion of the block transfer, the host must supply:
the logical rack address
the block-transfer module slot address
the data size to read from the module
a unique transaction number
As many as 64 block-transfer commands can be queued at one time, with
the limitation of one BT per block-transfer module (as many as 16 BTs per
logical rack). The scanner sets a 4 second timer for each BT request. If
the timer expires before the BT exchange with the adapter completes, the
BT request is cancelled and a confirmation is returned to the host
indicating there was a BT timeout.
Command Syntax
host_command
5
transaction_number
0 - 255
command_length
3
module_slot_address
0 - 15
logical_rack_address
0 - 31
bt_data_len
# of data words
1
1
You can specify 0 - 63; if you specify 0, the adapter decides the data length.
This command queues a confirmation when the block transfer exchange is
completed, i.e., it has received a BT reply packet from the adapter, or when
the 4 second timer has expired. The confirmation looks like:
Host BT Read Confirmation
host_command
5
transaction_number
0 - 255 (whatever host supplied)
confirmation_status
(see Table 5.B)
confirmation_length
# of data bytes (if successful, otherwise 0)
bt_read_data
1 - 64 words of data
Host BT Read
