BU-61582 データシートの表示（PDF） - Unspecified
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BU-61582 Datasheet PDF : 48 Pages
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CONFIGURATION
REGISTER #1
15 13
0
STACK
POINTERS
CURRENT
AREA B/A
DESCRIPTOR
STACK
LOOK-UP TABLES
BLOCK STATUS WORD
TIME TAG WORD
DATA BLOCK POINTER
RECEIVED COMMAND
WORD
LOOK-UP
TABLE
ADDRESS
LOOK-UP TABLE
ENTRY
Notes:
1. TX/RX/BCST_SA look-up table entry is updated following valid receive (broadcast) message
or following completion of transit message
CIRCULAR
DATA BUFFER*
(128,256,...8192 WORDS)
POINTER TO
CURRENT
DATA BLOCK
POINTER TO
NEXT DATA
BLOCK *
RECEIVED
(TRANSMITTED)
MESSAGE
DATA
(NEXT LOCATION)
50%
CIRCULAR
BUFFER
ROLLOVER
INTERRUPT
100%
CIRCULAR
BUFFER
ROLLOVER
INTERRUPT
FIGURE 6. RT MEMORY MANAGEMENT: CIRCULAR BUFFER MODE
CIRCULAR BUFFER MODE
FIGURE 6 illustrates the RT circular buffer memory manage-
ment scheme. The circular buffer mode facilitates bulk data
transfers. The size of the RT circular buffer, shown on the right
side of the figure, is programmable from 128 to 8192 words (in
even powers of 2) by the respective Subaddress Control Word.
As in the single message mode, the host processor initially
loads the individual Lookup Table entries. At the start of each
message, the SP’ACE stores the Lookup Table entry in the third
position of the respective message block descriptor in the stack
area of RAM, as in the Single Message mode. The SP’ACE
transfers Receive or Transmit Data Words to (from) the circular
buffer, starting at the location referenced by the Lookup Table
pointer.
At the end of a valid (or, optionally, invalid) message, the value of
the Lookup Table entry updates to the next location after the last
address accessed for the current message. As a result, Data
Words for the next message directed to the same Tx/RX(/Bcst)
subaddress will be accessed from the next contiguous block of
address locations within the circular buffer. As a recommended
option, the Lookup Table pointers may be programmed to not
update following an invalid receive (or broadcast) message. This
allows the 1553 bus controller to retry the failed message, result-
ing in the valid (retried) data overwriting the invalid data. This
eliminates overhead for the RT’s host processor. When the
pointer reaches the lower boundary of the circular buffer (locat-
ed at 128, 256, . . . 8192-word boundaries in the BU-61582
address space), the pointer moves to the top boundary of the cir-
cular buffer, as FIGURE 6 shows.
IMPLEMENTING BULK DATA TRANSFERS
The use of the Circular Buffer scheme is ideal for bulk data trans-
fers; that is, multiple messages to/from the same subaddress.
The recommendation for such applications is to enable the cir-
cular buffer interrupt request. By so doing, the routine transfer of
multiple messages to the selected subaddress, including errors
and retries, is transparent to the RT’s host processor. By strate-
gically initializing the subaddress’s Lookup Table pointer prior to
the start of the bulk transfer, the BU-61582 may be configured to
issue an interrupt request only after it has received the anticipat-
ed number of valid Data Words to the designated subaddress.
SUBADDRESS DOUBLE BUFFERING MODE
For receive (and broadcast) subaddresses, the BU-61582 RT
offers a third memory management option, Subaddress Double
Buffering. Subaddress double buffering provides a means of
ensuring data consistency. FIGURE 7 illustrates the RT
Subaddress Double Buffering scheme. Like the Single Message
and Circular Buffer modes, the Double Buffering mode may be
selected on a subaddress basis by means of the Subaddress
Control Word. The purpose of the Double Buffering mode is to
provide the host processor a convenient means of accessing the
most recent, valid data received to a given subaddress. This
serves to ensure the highest possible degree of data consisten-
cy by allocating two 32-bit Data Word blocks for each individual
receive (and/or broadcast) subaddress.
At a given point in time, one of the two blocks will be designated
as the “active” 1553 data block while the other will be designat-
ed as the “inactive” block. The Data Words from the next receive
message to that subaddress will be stored in the “active” block.
Data Device Corporation
www.ddc-web.com
18
BU-61582
M-08/04-0
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