libusb and OpenOCD?

Hi John,

There is some information on libusbx here - basically at the time I did have a discussion with the developers (they have a very responsive e-mail group and are very helpful) and they mentioned that the project was created because libusb was slow in improvements and had infrequent releases - so I went with the more 'dynamic' fork :-) @selsinork has provided lots of useful information in the comments at that URL by the way.

I've not used OpenOCD before however.

EDIT): A google search reveals that there is a kickstarter called 'laika' which looks like pretty much an FTDI chip and the libusb and libftdi code, so that's confirmation that libusb works on the RPI. I couldn't find the schematic however - if it is intentionally unavailable then to me it seems rather mean considering it looks like an educational project. Maybe they do intend on revealing it. Still, the URL mentioned above should be sufficient information for anyone to make their own equivalent easily, since the FTDI chips are so integrated..

Thank you so much, shabaz.  Your 'blog post is exactly what I need to get started.  I already have an FT2232H Mini-Module (it's abot 60% down on the page) which I've used on Windows 2000 with FTDI drivers.  Now that my main development system is Ubuntu, I'll switch my code over to libftdi.  One nice thing about libftdi is that I can let it worry about which libusb API to use.  Eventually I'll "eliminate the middleman" and go directly to libusb, but the first device I need to talk to is the FT2232H so libftdi is the obvious way to do.  Your 'blog will be very helpful.

Hi John,

You're welcome! I hope it helps.

John Beetem wrote:

 

I have a some questions about libusb and OpenOCD.  There might be a better group to ask about these, but a number of people who comment in this group know about these sorts of things.  Besides, I will want to run this stuff on RasPi so it applies.

I can see no reason why libusb won't work on the Pi, but haven't specifically tried myself. Not sure if the combination of OOCD on a low powered Pi with known usb problems would fill me with confidence though.

I don't want to write a device driver -- I want to do everything from Userland.

You mean you want to write a userspace device driver

1.  There are several versions of libusb out there, and it appears to have an interesting FLOSS history.  There's libusb-0.1 which is old, but stable.  There's libusb-1.0 which has a different API, but it's actively being developed.  Then there's libusbx which is a fork of libusb-1.0, but it may have rejoined since libusb.org today lists libusbx-1.0.16 (2013-07-11) as the latest version.  Has anyone here developed with any of version of libusb and has some tips to share?  Also, does anyone here know about libusb history?

currently I'd chose libusbx-1.0, there's a compatability layer as a separate package for anything that needs libusb-0.1.

for various obvious reasons, you can't have both libusb and libusbx installed in parallel, libusbx is trying to be a drop-in replacement and as such uses exactly the same soname, so you have to make a choice.

As usual with forks, the background is political, so some research on the history is probably a good idea before making a choice.

libusbx.org is at 1.0.17, so I'm not sure what libusb.org having 1.0.16 shows.

Looking at the source repo on libusb.org shows the last change here http://libusb.org/changeset/7634714aa696175b08016b6f2185a75a2f55a113/libusb/ which was a year ago and their repo has a last tag of 1.0.9 - I think this 'no progress' was a large part of the reason for the libusbx fork.

A little mailing list search reveals this:

http://marc.info/?l=libusb-devel&m=137088260618024&w=2

so reading between the lines, the original libusb is dead and libusbx is the new libusb. In my mind, this is a good thing, especially as the github direction they seem to want to take is far better than the existing Trac (no, I'm not a great fan of github either, but it mostly works and git trees are easy to clone from there).

2.  Is there any better libusb documentation that what's available at libusb.org?  Google found me this this tutorial from Jan 2010, which seems to be a good start.  I'd appreciate any pointers.  There's no point doing "program by experiment" if someone has already done it and written it up.

 

I'd probably try http://libusbx.sourceforge.net/api-1.0/index.html not sure how good it is, but it has to be better than the older stuff.

Most of what I've done has been with libftdi, so a lot of what little I've learned has been from looking at how libftdi uses libusb, nothing like a working example .  I've also found it fairly easy to move this sort of code between linux and windows.

I'm also interested in OpenOCD.  Has anyone here used it at the API level?

Not yet, I've still not finished my OOCDLink-h based design as I haven't really found a need so far.

Certainly have a read at the discussion in the blog post shabaz linked to as well

John Beetem wrote:

 

Now that my main development system is Ubuntu, I'll switch my code over to libftdi.

I successfully did libftdi / libusb code on windows with reference to this blog post:

http://embedded-funk.blogspot.co.uk/2013/03/libftdi-under-windows.html

biggest problem for me was working out how to get a windows app that didn't open any sort of window, but that's another story...

OK, I'm making progress.  I got the "simple.c" and "find_all.c" examples working, so libftdi is able to see my FT2232H Mini-Module.  I'm still on Ubuntu 11.10 [*] so it apt-got libftdi 0.19 and still has libusb-0.1, but that should be OK for now.

I didn't have to uninstall ftdi_sio explicitly: libftdi did that for me automatically.  I did have to sudo, which is an annoyance.

Onward to MPSSE, JTAG, and eternal youth!

[*] Why Ubuntu 11.10?  Two reasons: (1) I hate upgrading software and (2) I used a Univac 1110 in my undergrad days, so nostalgia I guess.

John Beetem wrote:

 

I did have to sudo, which is an annoyance.

https://github.com/libusbx/libusbx/wiki/FAQ#wiki-Can_I_run_libusbx_applications_on_Linux_without_root_privilege

however, with an old enough setup it may be using /proc/bus/usb instead of /dev/bus/usb and so different steps need to be taken.  I don't follow ubuntu, so have no idea what needs done for 11.10, but I'd be surprised if it's still using the /proc interface.  I have a vague memory that you could compile libusb in a way that disabled the new interface and that I had to do that at one point when libusb wasn't keeping up with kernel changes.

johnbeetem wrote:

 

Onward to MPSSE, JTAG, and eternal youth!

Yes!  MPSSE and JTAG work very nicely.  It's so nice to be talking to my Mini-Module from GNU/Linux instead of Windows, and without the obscurity of proprietary drivers.  I really prefer the libftdi calls to FTDI's.

But now for something completely different... PSoC5!  (to be continued...)

Thank you again for your help.

Oh, awesome!!

That's good news. I didn't get a chance to try this out at the time but I was wondering how easy/hard it was to use, or if I should stick with the few off-the-shelf USB-JTAG devices that I have. Glad it works!!