Figure 130 Flow Chart For Read Operation - Microchip Technology Microsemi SmartFusion2 User Manual

DDR Bridge
Figure 130 • Flow Chart for Read Operation
Send read request to arbiter. Make AHB master
ready High. Initiate single read transaction.
The read buffer is invalidated under the following conditions:
• If the address from the master is outside the TAG region, the current data in the read buffer is
invalidated (TAG mismatch).
• To ensure proper data coherency, every master's write address is tracked. If an address matches
that of the read buffer TAG, the read entry is invalidated.
• A non-bufferable or locked transaction is initiated by any master.
• An Invalidate command is issued.
• A buffer disable command is issued.
• An error response from DDR for the expected word read.
5.1.2.3 Arbiter
The DDR bridge arbiter includes two independent arbitration controllers for read and write requests.
5.1.2.3.1 Write Access Controller
The write access controller (WAC) arbitrates write requests from the WCBs and grants access to one of
the requesting masters based on its priority. All transactions from a single master have a dedicated
master ID.
Combinations of fixed and round robin priorities are assigned to the following masters:
• Master Interface 1: Fixed first priority (Master Interface 0 is read only)
• Round robin between Master Interface 2 and Master Interface 3 for second and third priorities
Once a burst transaction is initiated to the external DDR memory, the transactions are completed without
an interruption. No other master, even a high priority master, can interrupt this process. Subsequent write
requests from the same master are held until the previous write transactions are completed to the
external DDR memory. Subsequent write requests from other masters can be accepted and allowed to
Start
Read request = 1
NO
YES
Other master is holding
the read transaction?
YES
NO
NO
Non bufferable read
request?
YES
Make ready high. Read data from
buffer and send it to Master
Microsemi Proprietary UG0446 User Guide Revision 7.0
YES
Read buffer is
empty?
NO
NO
Send read request to arbiter with burst size
Read address is
of read buffer size. Send expected word to
matching with buffer
tag?
YES
AHB Master
211