Software :: Delay When Reading From An USB-A-port?
Jun 29, 2010
Working on a project based on embedded linux. The system is based on an Atmel ARM9 processor.
On one of the ports, an USB-A, we are constantly talking with several pieces external equipment (hereafter called slaves) at the speed of 4800 baud.
The communication is designed so that one messages is sent to a certain slave. The answer is expected to arrive directly. If no answer is received within 2 seconds, the sent message is sent in a resend buffer, and will be sent next cycle.
My problem is now that sometimes, the answer isn't received in 2 seconds. But when the message to the next slave is sent, the answer from the previous slave is received.
That is at least how it looked like from my software point of view.
But, then I used a serial sniffer on the USB port, and found out that the answer actually did arrive in time. Thus the delay must be somewhere between the USB port and my software. Linux in other words?
My software uses standard functions read() and write() for the communication.
I am trying to read the /proc/net/tcp6 file of a huge server (chat server) for monitoring the tcp6 connection states.
This tcp6 file has more than 26000 lines. For monitoring the server connections, my monitoring tool has to read the /proc/net/tcp6 file quickly in regular interval. Presently it takes minimum 6-7 seconds for reading the whole file.
My tool can able to read the normal file (26,000 lines) less than 1 second, but it is not possible to read the same size of proc file.
I have 2 questions:
1) Why proc file takes more read time than normal file?
2) Is there any way to read the /proc/net/tcp6 file more quickly?
I have two usb2serial adapters connected to my PC with a null modem (I am doing some testing to learn serial comm for a particular application). I am writing to /dev/ttyUSB0 a trying to read /dev/ttyUSB1. I have used screen (screen /dev/ttyUSB1 115200) and am able to see the characters being written. I am also able to read and write with Python with the following code
I've got a box with 2 interfaces, with IP1 = 192.168.100.1 and IP2 = 10.1.1.1 respectively on them. I've got an iptables rule that looks like: Code: iptables -t nat -A POSTROUTING -s 192.168.100.0/24 -d 10.0.0.0/8 -p udp -j SNAT --to-source 10.1.1.1 --random
If I get 2 consecutive packets from the same address and port from 192.168.100.0/24, they get SNAT-ed and come out of the same port on 10.1.1.1. If then I get another packet from the same address and port 10 minutes later, then it gets SNAT-ed, but comes out of a different port on 10.1.1.1. My question is: how can I set the time delay I would like iptables to remember its incoming address/port to outgoing port mappings?
I have got a problem while reading from the serial port. I'm working on iMX-31 board and Eclipse IDE. Whenever I'm trying to read any data through the serial port, it's displaying I/O Possible and the application is being terminated. After reading I'm trying to write this data on a file. Here are the excerpts from the code:
After GRUB 2 comes up (I'm running Ubuntu 10.10) and I choose the OS to boot, there is about a 5 second delay where nothing appears to happen after I make the selection -- no disk activity. It happens consistently every time I boot. Again, this is after I choose the OS to boot, so it shouldn't have anything to do with the standard delay to allow me to choose the appropriate OS.Is there a good way to troubleshoot this and determine what is causing the delay?
I have an application where I am sending data via serial port from PC1 (Java App) and reading that data in PC2 (C++ App). The problem that I am facing is that my PC2 (C++ App) is not able to read complete data sent by PC1 i.e. from my PC1 I am sending 190 bytes but PC2 is able to read close to 140 bytes though I am trying to read in a loop.Below is code snippet of my C++ AppOpen the connection to serial port
I don't understand the results of a simple performance test I ran using two basic scripts (running on a high end server):
perfVar.zsh :
#!/bin/zsh -f MYVAR=`cat $1` for i in {1..10}
[code]...
Performance test result:
> time ./perfVar.zsh BigTextFile > /dev/null ./perfVar.zsh FE > /dev/null 6.86s user 0.32s system 100% cpu 7.177 total > time ./perfCat.zsh BigTextFile > /dev/null ./perfCat.zsh FE > /dev/null 0.01s user 0.10s system 91% cpu 0.118 total
I would have thought that accessing a VARIABLE was way faster than reading a FILE on the file system... Why this result ?Is there a way to optimize the perfCat.zsh script by reducing the number of accesses to the file system ?
i installed kernel 2.6.34 to fix my lid closing issue, and that went great. but now when i go to reinstall my broadcom i get this error. Code: Reading package lists... Done Building dependency tree Reading state information... Done bcmwl-kernel-source is already the newest version. 0 upgraded, 0 newly installed, 0 to remove and 1 not upgraded. 1 not fully installed or removed. After this operation, 0B of additional disk space will be used. Setting up bcmwl-kernel-source (5.60.48.36+bdcom-0ubuntu3) ... Removing old bcmwl-5.60.48.36+bdcom DKMS files...
I want to do a simple port redirect, i.e. whatever comes trough whatever interface on port AAAA will get redirected to port BBBBI thought that iptables -t nat -I PREROUTING --source 0/0 --destination 0/0 -p tcp --dport AAAA -j REDIRECT --to-ports BBBBhowever it doesn't work, e.g. nc -v -w2 -z localhost AAAA gives:
nc: connect to localhost port AAAA (tcp) failed: Connection refused while nc -v -w2 -z localhost BBBB
I have a mail server i need it to send message via port 587 not port 25, i make some changes to my postfix server which i use and it is already successed making a telnet to 587 port like it :
VERY new to linux, erm but I have an issue that needs solving!I recently moved to university, where their network blocks sftp port 22, this means that I cannot connect to my FTP server which is running a version of linux.Now I've got this ftp server connected to a seedbox and it was created using the following walk through..Code:I have written this guide for a friend, but I though it would be useful for others as well.
There are several guides floating around, but I found that most always cock up in some way. This one is tried and tested to work on Debian Etch (on an OVH rps, but should apply to most servers).If there is a new stable release of rtorrent/libtorrent then I will update this guide to show you how to update it (without reinstalling the whole server).
At the bottom there are also instructions to install ftp access & some network monitoring software.Basically, I would really like someone to be able to construct the commands on how to change the listen port for sftp connection on linux or add another port to the list that Linux would use so that I could put in through putty.
sudo ssh -L 750:192.168.123.103:873 username@192.168.123.103It does exactly what it's supposed to do, but how do i edit / remove this rule?Is there some config file where i can alter the forwarding? How does it get stored?Im using Ubuntu 10.10Server Edition (allthough i recon it would be pretty much the same across all versions
Is there any way to verify if packets being trafficked over a certain port are valid for the service you want to use this port for?
One obvious example that probably clarifies my question: When I open port 443 (outgoing or incoming) for https/ssl traffic, I don't want this port to be used for say openvpn traffic. Thus: when someone wants to surf to a website with https, it should be ok but if someone wants to connect to his home openvpn server over that same port, it should be blocked.
I'm not that great with mailservers, and just been thrown a curveball with a MS Exchange environment for which there is apparently no solution... yeah, right. But is there a workaround?
The problem is that the site mail (SMTP) needs to be sent via port 26 instead of the commonly used 25. Port 25 is mapped to a mailfilter, which apparently causes havoc with some of the mail, and the techs that have been on site trying to coax the Exchange server to co-operate have said that the only way would be to get rid of the filter.
The problem is that there are number of apps that are unable to have the outgoing port changed and so keep sending mail out on port 25.
I look after the Unix/Linux side of things at work, and I was wondering if there was an easy way to set up a Ubuntu box to receive mail on port 25 and just forward it to the MS box on port 26? So, in other words (and I hope this makes sense): monitor port 25, and forward whatever comes in on port 25 to the server on port 26. Simple portforwarding, or is it? What steps do I need to take?
everything works fine. I can log in, and local port forwarding is done. Otherwise when I use the command:
ssh user@ssh_server -R 5500:localhost:5500 -p 22
I get an error "remote port forwarding failed for listen port 5500". However when I try remote port forwarding in WinXP by use of putty there is no problem...
I'm trying to set rxtxSerial to work so a Java app has access to a serial port (via SiLabs CP210x driver, port /dev/ttyUSB0). When I use update-alternatives --config java, there are 3 alternatives which provide `java'. I have tried openJDK and Sun. Both fail but with completely different messages.
In SuSE firewall0. I do have a openSuse 11.4 and multiple IP addresses on eth0 interface
I run (trying to/have to) multiple TOMCAT servers.
I am trying to have each tomcat instance listen to on separate IP address for example:
What i am trying to do is to redirect
a) tomcat 1 -
a) tomcat 2 -
And so on.
I know that it has to be possible.
I do have just eth0/
Is is it possible. Do I have to create "vittual interfaces"? eth0:1, .......... and do redirection ?
"Server" has got just single interface - just 1 ethernet calbe goes to that server. I am planning to have 10-15 tomcat's on that server (I have to unfortunatley) and each has to run on port 80
Is it possible to "grant" permissions to normal users to run app on port 80 - that would solve me lots of problems if impossible to redirect.
I tried to setcap 'cap_net_bind_service=+ep' /path/to/tomcat ...... but no luck
i am running ncat (netcat's new version from nmap) on centos . I am listening on different ports. My question is , is it possible that when a connection is received on a port say 123, i redirect this connection to a different port and use the 123 port again for listening connections. ncat has an option -k which u can add with -l , it will force fully listen on the port. It can accept multiple connections on a single port but i want that once a client connects on to 123 port, he is forwarded to some other port and no longer on 123.
I'm using a Debian servers, as router/firwall.. I've two ethernet interfaces into the server, one for wan and one for lan. The i use SNAT so my LAN clients can access the internet throgh the debian router. That is working... Now i want to be able to access servers on the LAN site from the WAN site, and i wanna use port address translation (PAT). I have a FTP server running on a lan server, so i'm trying to portward port 21.
When people try to access my FTP from the WAN site, they are redirected to the local FTP server, and they are promted for crendentials, but when the credentials are typed, and the local ftp server should answer the wan request, the connections dies.
The wan clients are being promted for credentials, so they are redirected to the local lan server, but after that the connections dies, so i think there is some kind of nat problem, when the local lan server is trying to respond to the wan request..
I make an application on GNU/Linux which listening on a MULTICAST stream, so I open my unconnected socket, bind it on a MULTICAST address and a port, join the multicast group with the "setsockopt (IP_ADD_MEMBERSHIP)", then I receive datagram on my socket.
Now I've two different instances of the same application that run with their own MULTICAST address and port. And what I found strange is that, after a misconfiguration, I switch the ports, for example:
Emitting on 225.0.0.1/23451 and 225.0.0.2/23452 Receiving on 225.0.0.1/23452 and 225.0.0.2/23451
And my receiving part doesn't care about the MULTICAST address, it looks like the socket is listening on the port number only! I mean that the receiver [225.0.0.1/23452] take its datagrams from emitter [225.0.0.2/23452] and vice-versa!
I'll explain this in one sentence: Is it possible to program a port-binding shellcode in which people across the Internet can connect to, without being thwarted by the router blocking their data because the port its bound to doesn't allow port-forwarding
If I forward port 80 to port 3128 for squid with an iptable rule, does port 3128 have to be open on the firewall or is this all routed behind the firewall?
I have a mail server on which I would like to block port 25 on my eth0 for everyone except our external spam filter. the problem is that I want our users to be able to connect via port 10025 which is forwarded to port 25, which then is blocked...
what should I add/change to set up port forwarding of port 1000 to ip 192.168.1.200. also how to get the answer sent by 192.168.1.200 follow the same route used by the data received through port forwarding.
