Fabric DDR Subsystem
Microsemi ProprietaryUG0446 User Guide Revision 7.0
148
In the event of loss of FPLL lock, even though its output is not exactly in phase lock with the reference,
the FPLL still generates a clock. User logic in the FPGA fabric can use the FPLL_LOCK signal to prevent
communication with the FDDR subsystem during this time.
4.6.3.2
DDR_FIC
The following illustration shows the DDR_FIC block diagram.
Figure 77 •
DDR_FIC Block Diagram
Fabric masters can access the FDDR subsystem in the following ways:
•
Single AXI-64 interface
•
Single AHB-32 interface
•
Dual AHB-32 bit interfaces
If the AXI-64 interface is selected, the DDR_FIC acts as an AXI to AXI synchronous bridge and also
supports locked transactions. During locked transactions a user configurable 20-bit down counter keeps
track of the duration of the locked transfer. If the transfer is not completed before the down counter
reaches zero, a single clock cycle pulse interrupt is generated to the fabric interface.
If single or dual AHB-32 interfaces are selected, the DDR_FIC converts the single or dual 32-bit AHBL
master transactions from the FPGA fabric to 64-bit AXI transactions. The DDR bridge, which is
embedded as part of the DDR_FIC, is enabled in this case. The DDR bridge has an arbiter that uses a
round robin priority scheme on read and write requests from the two AHB masters. Refer to the
for a detailed description.
The DDR_FIC input interface is clocked by the FPGA fabric clock and the AXI transaction controller is
clocked by FDDR_CLK from the FDDR clock controller. Clock ratios between FDDR_CLK and DDR_FIC
clock can vary. Supported ratios are shown in the following table. Clock ratios can be configured through
Libero System-on-Chip (SoC) software or through the FDDR_FACC_DIVISOR_RATIO register.
Table 132 •
FDDR_CLK to FPGA Fabric Clock Ratios
DIVISOR_A[1:0]
DDR_FIC DIVISOR[2:0]
FDDR_CLK: FPGA FABRIC Clock Ratio
00
000
1:1
00
001
2:1
00
010
4:1
00
100
8:1
00
101
16:1
01
000
2:1
01
001
4:1
01
010
8:1
01
100
16:1
11
000
3:1
Configuration
Registers
16-Bit APB
Configuration Bus
64-Bit AXI / Single
32-Bit AHBL /
Dual 32-Bit AHBL
Slave Interface
MUX
DDR Bridge
AXI-AXI
Synchronous
Bridge
MUX
AHB
AHB
AXI
AXI
AXI
AXI Transaction
Controller