Achronix Speedster22i User Macro Guide - Manual (Page 180)

Memories LRAMFIFO
Speedster22i Macro Cell Library Achronix Semiconductor Proprietary PAGE 163
transferring the Read Pointer across clock domains. As an example, setting rdptr_sync_stages
to 2’b00 configures the read pointer synchronization circuit to have two back‐to‐back registers
in the Read Pointer Synchonizer. The default value of the rdptr_sync_stages parameter is
2’b00.
Table 6-53: Mapping rdptr_sync_stages Parameter Settings to Synchronization Stage Depth
rdptr_sync_stages Read Pointer Synchronization Stage Depth
2’b00 2
2’b01 3
2’b10 4
2’b11 5
Figure 6-34: Read Pointer Synchronizer Block Diagram
rst_sync_mode
The rst_sync_mode parameter affects the behavior of the reset operation of the write and read
pointers. When the rst_sync_mode parameter is set to 1’b0, both the read and write pointers
resets utilize the Reset Synchronizer circuitry. When the rst_sync_mode parameter is set to
1’b1 the rstn input must be synchronous to the wrclk/rdclk clock driving the FIFO. The default
value of the rst_sync_mode parameter is 1’b0.
wrrst_sync_stages
The wrrst_sync_stages parameter defines the number of stages of registers used to
synchronize the rstn input pin to the rdclk clock domain. The value of the wrrst_sync_stages
parameter is only used if the rst_sync_mode is set to 1’b0. The mapping of the
wrrst_sync_stages parameter value to the number of sychronization stages is defined in
Table
6‐54: Mapping wrrst_sync_stages Parameter Settings to Synchronization Stage Depth ,
where each stage corresponds to a register in Figure 6‐35: Write Pointer Reset Input
Selection Block Diagram . For example, setting wrrst_sync_stages to 2’b00 configures the rstn
synchronization circuit to have two back‐to‐back registers in the Write Reset Synchonizer. The
default value of the wrrst_sync_stages parameter is 2’b00.
Table 6-54: Mapping wrrst_sync_stages Parameter Settings to Synchronization Stage Depth
wrrst_sync_stages Write Reset Synchronization Stage Depth
2’b00 2
2’b01 3
2’b10 4
2’b11 5
Read
Pointer
Read Pointer Synchronizer
d q d q d q d q d q
rdclk
wrclk
ptr_sync_mode
rdptr_sync_stages
Synchronized
Read Pointer
used for flag
00
01
10
11
0
1
calculations