Description

Open FreeList Readme

General Description

The Open FreeList module is used to manage a set of variable sized packets inside a fixed memory block. The memory block is partitioned into fixed sized chunks and each packet uses one or more chunks. The module offers three possible actions:

1. Write a packet into memory
2. Read a packet from memory
3. Release a packet

Using the Module

Parameters

Name	Description	Unit	Default Value
RAM_W	Memory block width	bits	128
RAM_E	Memory block extra data	bits	0
RAM_S	Memory block size	KBytes	64
CHK_S	Chunk size	Bytes	128
RAM_TYPE	Memory block type	string	"MRAM"
FL_AEMPTY_LVL	FreeList almost empty level	#	2

Interface

Name	Direction	Width	Description
global signals
reset_n	input	1	async reset (active low)
clk	input	1	clock
write interface
fl_q	output	clog(#_of_chunks)	first chunk number for a new packet. capture this value and use it to read/release the packet
fl_aempty	output	1	indicates that the number of chunks reached the almost empty level
fl_empty	output	1	no more chunks available. do not write any more
wren	input	1	write pulse. writes the data on din into the memory block
din	input	RAM_W+RAM_E	data to write into memory block
eop	input	1	end-of-packet indication. assert on last write of packet
read interface
chunk_num	input	clog(#_of_chunks)	first chunk in a packet to be read or released
load_req	input	1	request to read a packet starting at chunk number 'chunk_num'
rel_req	input	1	request to release a packet starting at chunk number 'chunk_num'. also required after a packet is read
load_rel_ack	output	1	acknowledge a read or release request
rden	input	1	read request. data on 'dout' is valid one clock later
dout	output	RAM_W+RAM_E	data read from memory block

Operations

Write

To write a packet, do the following:

• make sure 'fl_empty' is de-asserted
• capture the value on 'fl_q'. it will be used later to reference this packet
• while 'fl_empty' is not asserted do:
• write the next data line in 'din'
• assert 'wren'
• on the last line of the packet, assert 'eop' as well

Read

To read a packet that was previously written, do the following:

• set 'chunk_num' to the value of the first chunk in the packet.
  this value was obtained from 'fl_q' when the packet was written
• assert 'load_req'
• when 'load_rel_ack' is asserted, for each line of data do:
• assert 'rden'
• capture 'dout' one cycle later

To determine the last line of data, you could:

• store the packet length in an external structure
• use the extra bits in the memory block to hold an indication such as end-of-packet

Note that the 'eop' indication that is written in the write operation is not available on a read operation.

Important: after a read is complete, a release operation must be explicitly performed. There is no need to set the 'chunk_num' value after a read operation. The chunks are released when the packet is read, but the last chunk requires an explicit release operation.

Release

A packet can be released under two circumstances:

1. when a read is complete, a release must be issued
2. if a packet is not needed, it can be released without reading it

To release a packet, do the following:

• set 'chunk_num' to the first chunk of the packet (not required after a read)
• assert 'rel_req'
• when 'load_rel_ack' is asserted, you are done

Memories

Three memories are used in this module:

1. ram - dual port memory. two cycles to read
2. free_list - single clock lookahead FIFO
3. link_list - dual port memory. two cycles to read

The target architecture is Altera Sratix. There should be matching memory blocks in other architectures.

Code: Alex Manash - Crescendo Networks
Docs: Amit Fridman - Crescendo Networks