Slow speed of UDP reception in Matlab - matlab

Question

My FPGA is sending UDP packets on network using 100 mbps ethernet and a have written a MATLAB code to capture the data. The problem is i am getting very low speed in MATLAB around 50 kbps during reception. FPGA kit is connected to a gbps switch and then to PC. No internet cable in the switch.
I am pasting the matlab code below. If i try to increase the speed by increasing buffer size, the packets are dropped. current settings are through hit and trial on which i receive all data successfully. IS there any way to increase data reception speed in MATLAB?
Code:: (UDP from FPGA to Matlab)
clc
clear all
close all
u=udp('192.168.0.100','RemotePort',4660,'Localport',4661);
set(u,'DatagramTerminateMode','off');
set(u, 'InputBufferSize', 18);
set(u,'Timeout',0.1);
fopen(u);
x=tic;
for i =1:1000
a(:,i) = fread(u,18);
end
fclose(u);
delete(u);
t=toc(x);
bw = (1000*18*8)/t;
/////////////////////////////////////////////////////////
A MODIFIED VERSION OF THE ABOVE CODE (EASE OF UNDERSTANDING) + IMAGE Showing the PROBLEM
also: An image showing Data Variable with a buffer size of 20 Packets (18 bytes / Packet). Data must not be all zero as pointed in the image. It represents missed packets.
/////////////////////////////////////////////////////////
clc
clear all
close all
packet_size = 18; % Size of 1 Packet
buffer_size = 1*packet_size; % Buffer to store 1024 packets each of Packet_Size
buffer_read_count = 10; % How many times the buffer must be read
u=udp('192.168.0.100','RemotePort',4660,'Localport',4661);
set(u,'DatagramTerminateMode','off');
set(u, 'InputBufferSize', buffer_size);
set(u,'Timeout',0.5);
fopen(u);
x=tic;
for i =1:buffer_read_count
[a, count] = fread(u,buffer_size); % Read the complete buffer in one Fread()
if (count == buffer_size)
data(:, i) = a; %If Read_BYtes(Count) == BufferSize Store in Data
end
end
fclose(u);
delete(u);
t=toc(x);
bw = (buffer_read_count*buffer_size*8)/t; %Speed / BW of UDP Reception

Answer 1

I looked at your code and found some basic corrections, let me know if it speed up your code.
u=udp('192.168.0.100','RemotePort',4660,'Localport',4661);
set(u,'DatagramTerminateMode','off', ...
'InputBufferSize', 18, ...
'Timeout',0.1); % I think only one call of set is needed here
fopen(u);
x=tic;
% The variable a is not pre-allocated before the loop
a = zeros(YourNumberOfLine, 1000)
for ii =1:1000 % Always use ii and jj and not i and j
a(:,ii) = fread(u,18);
end
fclose(u);
delete(u);
t=toc(x);
bw = (1000*18*8)/t;

Answer 2

Let me summarize my comments.
Low code efficiency
As #m_power has pointed out, using i and j slows down your code by a bit. See this for more information. In Matlab, you should always use ii and jj instead.
You didn't initialize data. See how Mathworks explain this. If #1 "slows by a bit", #2 then slows a lot.
Since your code is slow, it's not guaranteed that each time FPGA sends a packet, your PC is able to find any available buffer to receive the packet.
Full buffer
if (count == buffer_size)
data(:, i) = a; %If Read_BYtes(Count) == BufferSize Store in Data
end
So if the packet is smaller than the buffer, data(:,i) = nothing? That is the most possible reason why you are getting zeros in column 3,4,and 5.
Empty buffer
Zeros in column 3, 4 and 5 may also originate from an empty buffer, if you have done the previous changes. The buffer is not guaranteed to carry something when Matlab reads it, so some for iterations may catch zero-length contents, data(:,ii) = 0.
Use a while loop to solve this issue. Only count for non-empty buffer readings.
ii = 0;
while (ii < buffer_read_count)
[a, count] = fread(u, buffer_size);
if count % non-empty reading
ii = ii+1;
data(1:count,ii) = a;
end
end
....incomplete packets?
You wait for a full buffer, because each time you want to read an entire packet? I suddenly realized it; how stupid I was!
But what you have done is keeping reading the buffer, and throwing away the data as long as it's shorter than the buffer length.
Instead, you'll need aggregate the data in each loop.
data = zeros(buffer_size, buffer_read_count);
total_size = buffer_read_count*buffer_size;
ptr = 1; % 1-D array index of data
while (ptr < total_size)
[a, count] = fread(u, buffer_size);
if count % non-empty reading
if ( (ptr+count) > total_size )
data(ptr:end) = a(1:(total_size-ptr+1));
ptr = total_size;
else
data( ptr:(ptr+count-1) ) = a;
ptr = ptr+count;
end
end
end
Test - I changed fread to a random integer generator with ii remembering how many times the buffer is read.
clear all;clc;
buffer_size = 18;
buffer_read_count = 10;
data = zeros(buffer_size, buffer_read_count);
total_size = buffer_read_count*buffer_size;
ptr = 1; % 1-D array index of data
ii = 1;
while (ptr < total_size)
count = randi(buffer_size);
a = randi(9, count, 1) + ii*10; % 10's show number of buffer readings
ii = ii+1;
% [a, count] = fread(u, buffer_size);
if count % non-empty reading
if ( (ptr+count) > total_size )
data(ptr:end) = a(1:(total_size-ptr+1));
ptr = total_size;
else
data( ptr:(ptr+count-1) ) = a;
ptr = ptr+count;
end
end
end
disp(data)
The result is
13 38 51 63 72 93 104 125 141 164
12 35 53 63 73 96 101 123 148 168
14 33 55 68 72 99 106 124 142 168
14 37 51 69 77 91 109 127 145 165
12 33 57 66 76 96 114 137 143 168
14 39 56 63 72 94 117 139 144 169
11 46 55 61 72 93 111 139 146 164
16 42 58 68 75 93 119 135 153 164
26 41 58 66 79 109 126 139 152 166
33 43 58 69 75 102 122 132 152 177
35 48 53 61 81 108 125 131 153 174
36 49 55 66 95 102 125 133 165 177
31 47 57 63 94 109 129 136 164 179
35 47 51 72 98 108 128 135 162 175
36 43 51 74 94 104 129 139 169 175
32 46 53 74 95 107 127 144 164 173
38 48 55 78 97 105 124 145 168 171
39 44 59 77 98 108 129 147 166 172
As you can see, each time the length of fread output is either equal to or less than the buffer size. But it only jumps to the next column when the current one has been completely received.