Writing and reading a mixed-width fifo, Limitations of concurrent read/write operations – Achronix Speedster22i User Macro Guide User Manual
Page 163
Memories
BRAM80KFIFO
Speedster22i Macro Cell Library
PAGE 146
Writing and Reading a Mixed-Width FIFO
Figure 6-21: Writing and Reading a Mixed-Width FIFO
Limitations of Concurrent Read/Write Operations
FIFO operations may be performed simultaneously from both sides of the memory, however
there is a restriction with memory collisions. A memory collision is defined as the condition
where both of the ports access the same memory address within the same clock cycle (both
ports connected to the same clock), or within a TBD ps window (if each port is connected to a
different clock). If one of the ports is writing an address while the other port is reading the
same address, the write operation will occur, but the read data will be invalid. If the user
programs either the en_wr_when_full or en_rd_when_empty parameters to 1’b1, it is possible
for simultaneous memory operations to occur, resulting in corrupted reads from the FIFO.
Even though memory collisions corrupt the read data, no damage to the hardware will occur.
wrclk
rdclk
wren
rden
din
dout
empty
almost_empty
2. wptr_sync_stages = 2’b00
Note: This timing diagram assumes:
3. sync_mode = 1’b0
4. fwft = 1’b0
word 0
word 0[15:0]
word 1
word 0[31:16] word 1[15:0] word 1[31:16]
1. write_width = 32, read_width = 16