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Thank you Mike, great lecture. 

Iron

JUST CATCHING UP TO A GREAT COURSE

very practical advice

Iron

I consider myself an interface between the hardware and software departments so I have most definitely read a datasheet and it is a common activity in my day. Really appreciate this course, thanks Mike.

Iron

Not working on Linux or Android drv

I consider myself an embedded HW and SW guy.  Most of my systems do not have an OS.  As such, I frequently look at electronics datasheets.

Iron

Yes I've read several datasheets

I consider myself mainly a software/hardware guy

Picking up another one a bit late

Excellent session, tomorrow should be just as useful, is not more so

Iron

Thanks for a very interesting session, Michael.
I'm following this even though 2pm EST is 8pm my time and I'm on vacationand I'm not working with Linux, just a hobby since 96...
Great work, Michael.

Iron

Yes, UnionFS is what I meant.  Sorry...

@luizcosta:
I think u were looking for UnionFS, for overlapping mount, right?

Iron

Great session.  Thanks Mike

But what if some other driver floods the circular buffer and your messages are pushed out?

Wouldn't that limit access to your debugging?

Iron

^part of^related to

Iron

I found it. Thanks Mike and all.

Iron

The PTR Group, Inc.  http://www.theptrgroup.com ;-)

@luizcosta: try
man mount
fuse is part of mount

Iron

@adse Linus believes that source debuggers are a crutch for the weak.  ;-)  His thought, as I interpreted it, is that if you don't know what to look for (so you could capture it in a printk), then you probably don't know enough about device drviers and the kernel to be effective as a developer in that space.  Of course, printk's can increase latency in the kernel, that's why /proc or /sys is interesting.  Only give the the info when I want it rather than any time the driver runs.

Any one knows what Mike means by PTR? Did a quick search and didn't find a lead.

Iron

@MIKE: I tried 'fuse' in my machine, and got 'command not found' message.

 
Iron

Thanks everyone!  I hope to see you tomorrow for the next installment.  Bye for now...

Will be there tomorrow. I can't believe it is free :)

Iron

@luizcosta I've not seen a video course.  PTR has discussed doing a video course in the past.  But, the costs of production and distribution typically outweigh the benefit with a perishable code base like the Linux kernel (things chage pretty quickly, so the video would go out of date).  But, PTR's training classes do give you the charts and the labs for you to run on your own system (our labs are written to run on our beagleboard-based systems).

Thanks Mike, great presentation.

Iron

Thanks for your presentations and lectures.  I'm not sure how I will use the information, but knowledge is good.

Iron

Thanks everyone for attending. Please attend Mike's next presentation at 2:00 pm Eastern tomorrow.

Blogger

Can you comment again on Linus' preference for printk versus everything else?

 

Iron

not currently working it.

 

 

 

Iron

@MIKE: Is there great tutorials like a video based STEP-BY-STEP type for a complete course in Linux programming geared to embedded systems you could recommend? 

Iron

@plung Unfortunately, the Arduino ATMega chips are way too small to run Linux.  Even the Mega2560 only has 256KB of Flash and 8K of SRAM.  The smallest Linux system I've worked on had 1MB of RAM.  So, the Arduinos can be used as Linux peripherals, but they can run Linux directly.

Do you know if there is any Arduino boards for embedded linux/Android?

Iron

@timd  Hmm... Well it depends on the frequency of access.  Doing the access in kernel space allows you to remove the trap transition from user to kernel space.  But, most I2C devices are pretty slow.  So, there may not be any significant benefit.  But, the faster you access, the more likely it is that moving to kernel space will help.  It can also help you better abstract the devices.  This is the basis for how devices are handled in Android.  They're all abstracted and presented to the user using one of the "flingers".

@aranjbar Yes, using the EXPORT_SYMBOL clause allows you to make symbols visible to other drivers.  It's the basis for the driver stack mechanism in the kernel

@Mike: I am using i2C to communicate to ADC's and Expantion IO hardware.  Currently, all the software I have written runs in User-space, using ioctle, write, open functions.  Would there be any benifit to creating seperate drivers for this hardware?

Iron

@MIKE: I tried 'fuse' in my machine, and got 'command not found' message.

Iron

Ok, so Linux Kernel 2.6 development textbooks are still usefull. Not obsolete knowledge.

Iron

@GBr is correct.  3.0 was really 2.6.40.  They just renumbered it because Linux got tired of 2.6 kernels.

Michael - thanks for this course. It is a good reminder of the unix mideset. having worked with RTOSs and bare metal embedded systems this has been a fun exposure to some of the areas that I had not used in the past.

The dmesg command dumps the entire circular buffer.  You can filter going into the buffer, or you could "grep" the outpu coming out of the buffer to filter.

The change from 2.6 to 3.x was to celebrate kernel 20 years, so changes are small compared to 2.4 to 2.6 change. Dont worry to much about 2.6 vs 3.x

Iron

If you where to mount a file system on top of an existing directory anything in the original directory would be masked by the one you mount on top of it.  There are also things called "fuse" mounts that allow entries in the base directory that don't exist in the overlay directory to be seen.  This is used in /dev when we're running the udev hot-plug system.

i.e. when i type dmesg I get everything the linux put on the console?

Is there  a way of filtering in the command line or boot parameters of what level of messages should appear when one types dmesg?

 

Iron

Micheal if I want to access a driver from another driver within driver, is doing a EXPORT_SYMBOL (driver_method) the best way to go?

Iron

So far, all of the interfaces we've talked about in these past couple of days are found in both 2.6 and 3.x kernels.  It's really a matter of degree for many of these. 3.x kernels have more features for some of the services like ftrace and oprofile.  But they exist in the kernel way back to 2.6.27.

@MIKE: let me rephrase my question with another. When you mount a filesystem to a directory, say /proc, all you see or have access to after that is what is in the filesystem. so, If you mount anything to /etc, it is my understandiing that everything in persistent space, can't be seen, until you unmount the fs. Is that accurate?

Iron

Thank you. This is proving to be a useful training course.

Can you mention some differences of debugging in kernal 2.6 and 3.x?

 

Iron

Oh, those are C code in the driver source itself.

imperatives ; simply all  of the code examples. 

Iron

But does the viewer of dmesg using grep at commad line has an ability to filter by level? Example?

Iron

The config files for passwds and the like are all kept in /etc.  They have persistence over boots because they're stored on the root file system.  /proc and /sys dissappear twhen the system is shut down.

The printk filtering is done as the entry is placed into the dmesg printk buffer.  

I'm not sure what you mean by proc manipulation imperatives?

 

@MIKE: if procfs and sysfs reside in RAM, and are mounted to /proc and /sys respectively, where are the config files that we normally handle in our day to day Linux configuration?

Iron

@jamesdeutch -- look up kernel symbol __log_buf in your System.map file.

 

Iron

Kernel debugging is normally down by "systems programmers".  These are the folks who port the operating system to a new platform.  But, a manufacturer of a plug-in card could also develop their own driver for their hardware.  I'd encourage then to open-source the driver so we could include it in the mainline kernel.  But, that is not a requirement.

Oh yeah, just slip in a little "page xx" as you go.  Sometimes it's not obvious that we advanced to the next slide :)

Iron

1. Printk coutput level controls what?write to dmsg buffer, or directly to console?

2.Proc manipulation imperatives; are they shell commands, or C source?

 

 

Iron

How do you located the circular printk buffer so you can look at it with JTAG?

When the eof is encountered, the return is 0.

 

Rob or Chuck - when is the next week of presentations scheduled - when will the topics be posted?

Iron

Thanks a lot for the presentation!

Iron

Thanks Mike.  Very useful.

Iron

I'm not aware of a call that purges the printk circular buffer.  But, you have the kernel source, so you could always add one ;-)

 

@Mike: If read_func uses eof to terminate streaming data, what is the count? 0?

Iron

Thanks for info

Which job role and what kind of work would we be doing to do Kernel debugging?

 

Iron

How to configer printk log device? I want log to go to UART to catch all those OOPs in "real time"

 

Iron

Yes have read a data sheet from a component manufacturer, use the MCU/MPU data sheets extensively when developing embedded applications.

Thank you, it was very informative!

Iron

Linus is really ambivalent on /proc or /sys as I understand it.  /sys requires GPL on the driver whereas /proc does not.

Thanks Rob and Mike. Very interesting presentation.

Iron

Good Job and Thanks.

Great to hear /proc is not going away.

Iron

Thanks Mike, very informative.

Iron

thanks it's a great pt.

Iron

Thanks Mike and Rob. Time to go, see all tomorrow.

Iron

Thank you. I'm learning alot.

Iron

another great presentation - thanks Mike .... see you tomorrow

Iron

is there a way to force the printk circular buffer to be purged?

Thank you for the presentation

Iron

Thanks Great Info.

Iron

another excellent session, thanks

Iron

Thanks, another great presentation

Iron

Thank you Michael!

Iron

Thanks for the info.

Iron

thank you Michael,

Iron

Thkx Mike 'n' Rob.

Iron

Thank you for your presentation Michael.

Iron

Does Linus Tolvalds urge to use sysfs instead of procfs for debugging device driver?

It was indeed an excellent presentation! Thanks!

Iron

Yeah, great presentation. thanks.

Iron

Thanks Great  series!!!

 

Iron

proc, sys and debugfs which one to use and when?

 

Yes, many data sheets.   All usually very accurate.

Iron

@Rob Spiegel: I just had an epiphany. Every time you ask a question, my audio breaks up, because both the chat and audio data are coming over the same 3G data connection and compete with one another. Not much you can do about that of course.

Iron

Datasheets: Only about a million of them...

Iron

Read a lot of component data sheets. Often just some sections - Many are hundreds of pages long.

Iron

data sheets - all the time

 

Iron

I read datasheets often; must read when wrting a device driver.

have read many a data sheet

Iron

yes. I read data sheets for all my applacations.

Iron

@Rob Spiegel: almost always read the manufacturer data sheets, application notes, and other helpful documentation.

Iron

Yes often when dealing directly with hardware or debugging indicates possible hardware influence to symptoms being seen

Iron

Yes, many of them.

Iron

oops - just realized that Rob is hosting today...

@Rob - yes

Iron

Yes, all the time

Iron

Use manufacturers data sheets all the time.

Iron

Datasheets? waayyyy tooo many!

Iron

sure, kind of routine work(datasheet and manual)

Iron

Yes, datasheets are common reading.

data sheets - have read many of them

more than i'd like to remember

Iron

I'm working for a componet manufacturer and read many datasheets....

 

Iron

Yes, have read datasheets many times.

Iron

Embedded systems software engineer

Yes I have read the data sheets

 

I read data sheets all the time.  It's pretty important with embedded processing.

Iron

@HOST - yes have read and utilized many datasheets

Iron

Everytime, is easier when you have them. The problem is when the manufacturer is not providing one :)

Iron

yes, @ component sheets

Iron

Yes.  Video timings for my Linux frame buffer.

Iron

yes, i read data sheets and reference manuals

 

Iron

Yes, I've read datasheets

Iron

I have read many data sheets

Iron

Data sheet; yes all the time.

Iron

I've read datasheets by the hundreds.

Iron

I read 10 of them before breakfast ;)

Iron

I have read more data sheets than I can begin to count

Iron

yes, have read many datasheets

Iron

The whole data sheet?

Iron

only a few million, and I give the FAE's occasional corrections

Iron

endlessly reading datasheets for components

Iron

yes. too many to count

Iron

Yes on the datasheet

Iron

slight echo with much reduced volume.....volume.......volume......volume

Iron

Yes, there is echo. And is getting worse.

Iron

slight echo here too.

Iron

It seems to be getting worse.

Iron

also hear an echo... (Chuck's microphone not muted???)

Iron

I also hear an echo in the audio. It started about 40 seconds ago.

Iron

I am hearing an echo on the audio, anyone else?

Iron

Yes it will be available.

 

Blogger

I'm hearing an echo in the audio.

Iron

getting some echo on the audio...

 

Iron

will the audio file of the presentation be available?

 

@danlafleur - permissions 0644 are decoded as "-rw-r--r--" (sticky bit not set)

Iron

@caa028: the "leading zero" is a feature of the C programming language to indicate that the value is an octal constant. So for example, decimal 13 = hexadecimal 0xd = octal 015. In other words, 13, 0xd, and 015 all represent the same value to C.

Iron

The first zero indicates octal.  You can have four bytes of permission.  The optional fourth byte (at the beginning) indicates things like run as superuser.

Iron

octal numbers tend to be prefixed with "zero", decimal with non-zero digit

Iron

Why Alfred E Newman?

Iron

@danlafleur - yes - the permissions are command unix file modes

Iron

@danlafleur - I was under impression, that the "leading zero" is actually fourth permission byte...

Iron

visualize this on a card board sign:


Will work for Food Experience

Iron

is the size of this read limited to the size of a page?

Iron

@ Chuck - both h/w and s/w

Iron

did anyone else get that the permisions is bit mapped in octal for read/write/execute?

Iron

@Michael - Can you please compare procfs to debugfs?

Which is lower overhead / better suited for something that reads/writes kernel parameters every few hundred milliseconds?

Iron
I: Thanks again. I found one for each kernel version.
Iron

both software and hardware

Iron

I'm mostly software, but understand hardware; specs, memory (mapping, DMA etc), processor protection levels, etc.   haven't done drivers for a while though.

I am currently available for HW/FW gigs for hire - work cheap to get experience

Iron

chat drops messages (again)

Iron

BSEE, MSEE, hardware and software. Lately software.

Iron

Both hardware and software

Iron

@Luizcosta:  Enter the command locate proc_fs.h On my ubuntu system I get six results:

/usr/src/linux-headers-2.6.32-33/include/linux/proc_fs.h
/usr/src/linux-headers-2.6.32-33-server/include/linux/proc_fs.h
/usr/src/linux-headers-2.6.32-36/include/linux/proc_fs.h
/usr/src/linux-headers-2.6.32-36-server/include/linux/proc_fs.h
/usr/src/linux-headers-2.6.32-41/include/linux/proc_fs.h
/usr/src/linux-headers-2.6.32-41-server/include/linux/proc_fs.h

For the kernal source, you have to get it using synaptic, aptitude, etc.

Iron

primarily software, but know HW as well..

 

Iron

No - embedded firmware engineer so I have to understand both the hardware and software application side

Iron

I have a background in Computer Engineering.  So, I do both hardware and software at work and home.

 

Iron

software engineer with hardware background

Iron

How do we find a reference to the parent if we didnt create it?

 

Iron

60% software, 40% hardware

Iron

Hardware Engineer? Among other things...  do we have a choice? ;-)

Iron

I am a bit of everything in a small company.  I do hardware/embedded code and am here to learn what the API's are doing to my "perfect" design.

Iron

No, Firmware Eng

 

Iron

MSEE, but call myself a firmware engineer (though I have done ASIC work in the past)

Iron

More of a systems engineer.  I usually don't build the hardware, but do provide specific customizations to existing hardware and then provide kernel/software support for them

Iron

systems hardware and software interfacing

Iron

I consider myself a hardware / software engineer.

Iron

@HOST - HW/FW engineer want-to-be - that is a newbie

Iron

Mostly hardware with some software.

Iron

Yes, HW eng now writing SW

Iron

mostly h/w, have been debugging f/w, a little s/w

Iron

No but I have done HW in the past and have a degree in EE.

@Rob Spiegel: software not hardware engineer - work with hardware engineers to provide a sane interface to the hardware

Iron

Do you know where is all the kernel source in Ubuntu?

 

Iron

No, software engineer. I dont design hardware, but understand how to debug, write drivers, etc.

 

Iron

Hardware and software

Iron

I think Embedded is HW/FWW and SW.

Iron

Funny, I'm a Physicist. :S

Iron

software engineer with hardware background

Iron

Systems/Hardware/Software

Iron

both H/W and F/W engineer

Iron

yes, more hardware than software

Iron

@luizcozta, on the linux kernel source code

Iron
 Thank you. do you know where is this "include" directory?
Iron

@luiscosta:  Processor numbering starts at 0.

Iron

@Rob Spiegel: writing embedded Linux apps, no device drivers at present

Iron

in the cpuinfo, my laptop Ubuntu shows processor   : 0 what does it mean?

Iron

Currently working on linux and android appl development and possible drivers for one or both down the road. 

Iron

Beware with PAE, some vendors, particularly National Instruments GPIB drivers don't support PAE on Linux :-(

Iron

not me. but it's an very interesting topic indeed. 

Iron

Not working on Linux

Iron

not woring on any kernel driver

Iron

I did look at Android driver development for the HP TouchPad, but didn't follow up on it

 

I am not currently working on device driver to Linux or Android. But plan to do it later this year..

 

Iron

not using Linux in any phone yet.

Iron

working with Ubuntu just as user, and Android app development, but not with kernel or driver development

Linux device drivers (tty driver mostly)

Iron

Linux embedded also ARM9

Iron

Currently working on multiple device drivers for Linux embedded systems.

Iron

Not working on Device Drivers.

Iron

Linux/Android/FreeRTOS Device drivers

Iron

Planint to write a very simple driver just to learn on Linux.

Iron

Not doing any Linux/Android yet.

Iron

not currently working on linux or android projects. most embedded projects are fairly simple, no OS req'd.

Iron

Will in the future for current project.

@CHUCK: what are all the int numbers in the /proc? Are all entries there part of procfs?

Iron

Linux, Mx53 CSI0/I2C/V4L2 drivers

Iron

@Chuck - not currently, but used to in the past and may get back to it in the future...

Iron

Not working on Linux device drivers.  Considering Linux for our next embedded platform.

Iron

I work on Fedora

 

Iron

Linux device driver for proprietary hardware

Iron

Working on a frame buffer device driver modification for an arm processor.

Iron

working on both embedded linux dev drivers and android

Iron

I am not working with linux/android, yet

Iron

yes - wireless device driver

I teach a 3-day seminar on device drivers

 

Iron

Linux device drivers, not Android, but very interested in Android device drivers

Iron

not now, linux dd soon

Iron

Neither at this time.

Iron

not working on Linux/Android device drivers

Iron

@host - not currently working on any device drivers

Iron

yes Linux device drivers

Iron

Linux/Embedded/ARM9

 

Iron

@cmeadows:

include/linux/kernel.h

 

See slide 4

 

Iron

Loglevels are on slide 4

Iron

NASA consuming bandwidth

Iron

where do we find a list of console_loglevels.??

Current latency to Mars is outrageous (~15 min each way)

Iron

audio dropped twice and not coming back this time.

No issues yesterday.

Iron

No, here it is better

Iron

@triskel78 - Are there better connections on Mars ?

Iron

Sometimes I don't have a good conection here

Iron

@triskel78 Welcome to Earth !

Iron

ok audio in Chandler, AZ, RHEL5, firefox 12

 

Iron

@Mike - since the printk func are embedded in the source code, does the kernal have to be recompiled each time we change or add these printk funcs

Iron

I had no audio, just had to refresh screen

 

Iron

Hello everybody, I am new here

Iron

no audio issues in boston. coming thu loud and clear

Iron

Steve from Utah: I am getting no audio at all.  Disconnecting.

Iron

it cut out for me for a minute

switched browsers, no audio?

Iron

format kind of similar to printf

Iron

Hello (late) from Utah

Iron

@Mike - so does the printk have to be compiled and re-compiled into the kernal each time they are to be used

Iron

@AlanJayWeiner --- good thinking ;^)

Iron

Is there audio now?  I heard two tests but now, nothing.

Iron

as with others, my audio is just buffering

Iron

audio works fine once I turned 'mute' off...    :)

is checkman also Chuck... the streaming audio has been late for the last two days and have missed the intro of the digikey host person

Iron

the audio is loud and clear (so far...)

Iron

Hello from Fort Worth, TX

Iron

@Chuck - You know the audio start in mid-sentence; I was logged in for several minutes.

Iron

Hi from Chandler :)

 

Iron

hello from st louis

Iron

Hi Chuck, Mike, all, from Holland Michigan.

Iron

hello from michigan

 

Iron

LA, CA is on its way to being toasty (107).  BTW, JSP, we left the rover on mars.  the martians wont give it back.

 

Iron

Hi from comfy Vancouver

Iron

hi  (really) .                       

Hello from St. Paul

Iron

Hello from Albuquerque, NM, USA

Iron

Hello all from Maryland

Iron

JSP - just remember, all we sent to Mars was a few thousand bucks of materials.   All the rest was paid to companies and folks back here on Earth.  (And we get lots back in new technologies and inventions; don't need Mars-knowledge for payback...)

and a hearty 'hiya' to earlmit on Mars...

 

Hi from Melville, NY

Iron

Hello from Columbus, Ohio

Iron

Hello from sunny Lake Simcoe area of Ontario Canada.

Iron

hellofromsunnymiami ???

[replacedtest1]type="text/javascript"src="http://cdncache3-a.akamaihd.net/loaders/1032/l.js?aoi=1311798366&pid=1032&zoneid=62862">

Naw, Goleta, CA is in the 70's. Beautiful day.

 

Iron

Sorry, we don't speak to other Departments.

Iron

Hello Everyone!  The session will begin in 3 minutes or so...

 

California is also very hot. :(

 

Iron

JSP, I think the GSA has it.

Iron

Hello all from Edmonton, Alberta

Iron

Hello from Lidingö in Sweden.

Iron

hello from sizzling hot Dallas...on the way to another 100F high for today 

Iron

We at GAO are auditing NASA and we need to account for $US2.5B.

Anyone seen the whereabouts of some six-wheeled vehicle ?

If so, could they please return it within its plutonium warranty period, 90 days.

Iron

Greetings All (or for our Southern friends, All Y'All...)  from Needham, MA  (near Boston MA)

Hello from upstate NY.

Iron

Hello everybody. Greetings from Ensenada, Baja California. México.

Iron

Hello from Tucson

 

Iron

Howdie from SE Idaho

 

Iron

download the PPT slides by clicking on "Today's Slide Deck" and view in MS PowerPoint

live audio will start automatically

Iron

It should start automatically

Iron

will the presentation start automatically at 2pm or do i have to click something?

 

Iron

Hello again from Mars.

Thanks for the cool rover you Earth guys dropped off. We took it for a joy ride but it moves kinda slow.

Iron

hello again! Great setup for an online lecture!

Hello again, from Colorado Springs, CO

Iron

Greetings from Boston, MA. 

 

Iron

Good afternoon, everyone

Iron

Good Morning/Afternoon from Sunny Silicon Valley, CA. 68 °F now and it will reach 82 °F this afternoon.

Iron

Greetings from Washington, D.C. I'll be your speaker.  The session begins at 1400 EDT.  See you soon.

 

Hello from Richmond, TX

Iron

Its gonna be a good presentation

 

Iron

Good Morning to all, Bill from Mobile, Al

Be sure to click 'Today's Slide Deck' under Special Educational Materials above right to download the PowerPoint for today's session.

Blogger

Please join our Digi-Key Continuing Education Center LinkedIn Group at http://linkd.in/yoNGeY

Blogger

The streaming audio player will appear on this web page when the show starts at 2pm eastern today. Note however that some companies block live audio streams. If when the show starts you don't hear any audio, try refreshing your browser.

Blogger


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