Subversion Repositories fade_ether_protocol

DESCRIPTION

This archive implements the simple and light protocol for transmission
of data from low resources FPGA connected to the Ethernet MAC
and an embedded system running Linux OS.
The main goal was to assure the reliable transmission over unreliable
Ethernet link without need to buffer significant amount of data
in the FPGA. This created a need to obtain possibly early 
acknowledgment of received packets from the embedded system,
and therefore the protocol had to be implemented in layer 3.

The Ethernet type 0xfade was used (unregistered, but as this
protocol should be used only in a small private networks,
without routers, with switches only, it should not be a problem).

We assume, that the FPGA is capable to store one "set" of packets
(in the example design length of this set is equal to 32).
To start the transmission, receiver sends the "start transmission"
packet:
TGT,SRC,0xfade,0x0001,pad to 64 bytes

After reception of the "start transmission" packet, the transmitter
(FPGA) starts to send the data packets:
TGT,SRC,0xfade,0xa5a5,set & packet number, delay, 1024 bytes of data


After reception of the correct data packet, the receiver sends the
"acknowledge" packet:
TGT,SRC,0xfade,0x0003,set & packet number, pad to 64 bytes

Another packet may be used to request immediate stop of transmission:
TGT,SRC,0xfade,0x0005, pad to 64 bytes

When first packets from the current set buffered in FPGA are 
transmitted and acknowledged, they may be replaced with the packets
from the next set - the current state of transmission is stored
in desc_memory in the desc_manager entity.

When particular packet is not acknowledged, it is transmitted once
again. In current example design each packet has simple attributes:
1. set number
2. valid (ready to be sent)
3. sent (has been sent at least once - used for delay adaptation)
4. confirmed (reception has been confirmed, packet may be replaced
   with the same packet from the next set)

List of packets is cyclically browsed to move the "head" and "tail"
pointers.
I've also tried another approach with more sophisticated packet
manager based on linked lists, but it is not fully debugged and not
ready for release yet. However the approach with cyclic browsing is
sufficient, as anyway an additional delay between packets had to be
introduced to achieve optimal transmission.

If the data packets are sent too quickly, the acknowledge
packets from the embedded system are received too late,
and the packet is retransmitted before acknowledge arrives.
The same may occur if the embedded system is overloaded 
with packets from different slaves and drops some packets.

Therefore paradoxically resending of packets as soon as possible
does not provide the maximal throughput, and a delay between
packets must be introduced.
Of course if this delay is too big, the transmission also slows down.

To find the optimal delay, I have implemented a simple adaptive
algorithm based on analysis of the ratio between number of all sent
packets and of retransmitted packets: Nretr/Nall
If the data packets are sent too quickly, the ratio of Nretr/Nall
increases indicating, that the delay should be higher.
If the ratio Nretr/Nall is near to 0, we may reduce the delay.
Such a simple algorithm works quite satisfactory.

In the embedded system, the fpga_l3_fade.ko driver allows you
to service multiple FPGA slaves connected to different network
interfaces.
The "max_slaves" parameter lets you to set the maximum number of 
slaves, when module is loaded.

After that, you can open /dev/l3_fpga0, /dev/l3_fpga1 ...
devices, to connect different slaves.
To connect one of those devices to particular FPGA slave,
you need to use the ioctl command L3_V1_IOC_STARTMAC 
(please see the attached receiver2.c application for
an example).
The data received from the FPGA are placed in a kernel
buffer (each subdevice has its own buffer) which may be mmapped
to the user space application, providing very quick access
to the data. Another ioctl commands:  L3_V1_IOC_READPTRS
and L3_V1_IOC_WRITEPTRS allow you to read the head and tail
pointers in this buffer and to confirm reception of data.
The attached receiver2.c application uses the described
mechanisms and simply tests, if the connected FPGA slave
sends consecutive 32-bit integers.

DISCLAIMER:
The published sources are "the first iteration". They work for me,
but I do not provide any warranty. You can use it only on your 
own risk!

I hope to prepare the new, more mature version, which will be 
described in a "official" publication (I'll send the reference, 
when it is ready).

I'll also publish further versions of sources on my website:
http://www.ise.pw.edu.pl/~wzab/fpga_l3_fade


LICENSING:
1. My kernel driver is released under the GPL license
2. My user space application is public domain
3. My FPGA code is published with BSD license
4. I include also very slightly modified Ethernet MAC 
   http://opencores.org/project,ethernet_tri_mode
   which is published under LGPL.
5. Due to licensing issues I can include only xco files for blocks
   generated by Xilinx tools (in case of sources for 
   Spartan 3E Starter Kit instead of binary dcm1.xaw file
   I had to include the generated dcm1.vhd file to avoid binary
   attachment in shar archive).
   I hope that you'll be able to rebuild my design with them

REBUILDING of FPGA CORES
The sources are split into two sections:
FPGA_with_MAC - this is the older version with Ethernet MAC taken from
                http://opencores.org/project,ethernet_tri_mode
FPGA_no_MAC - this is the newer version with renoved Ethernet MAC
              instead two small state machines are implemented in
              ethernet_sender_X and ethernet_receiver_X (X=4 or 8)
              controlling the PHY directly.

My sources have been tested with three boards: SP601, Atlys and
Spartan-3E Starter Kit. In the FPGA subdirectory there are
three subdirectories: sp601, atlys and sk3e. In each of those
subdirectories you there is the "build.sh" script, which
should recreate the .bit file needed to configure particular
board.

If you create something basing on this my work, I'll be glad if you
provide information about my project (especially if you cite my 
article, after it is ready and published)

EXPERIMENTAL 10Gb/s IMPLEMENTATION
In the directory experimental_fade_10g you can find experimental
version of my protocol, working with the 10Gb/s link on the 
KC705 board.
The design has been initially tested, and is working, but it still
needs some improvments.
Please note, that this version uses the "jumbo" frames,
with 8192 bytes of user data in each packet (plus header).
Therefore it was necessary to make some changes in the kernel
driver.