[time-nuts] FPGA GPSDO (Was: Re: NTP jitter with Linux)

[Javier Herrero]

El 07/04/2012 16:02, Jim Lux escribió:
> On 4/7/12 4:47 AM, Javier Herrero wrote:
>
> I'm very familiar with the LEON and RTEMS, having managed a software 
> development project with it for the last 3 or 4 years at work.
>
> http://www.gaisler.com/ for LEON
> http://www.rtems.org/ for RTEMS
I will have a look to RTEMS
>
> And yes, there is a port (maybe two) of Linux for the LEON as well (A 
> few years ago, we loaded up the Snapgear port, but since we went 
> RTEMS, I haven't fooled with it).  You'd have to check the Gaisler.com 
> website.
I've done. The Snapgear port is quite old now, but the other port is 
actively maintained and updated with current kernel.
>
> You can drop a LEON core into a Virtex II in about a day, and judging 
> from the traffic on the LEON yahoo list (where the Gaisler folks hang 
> out), lots of people are doing things like multiple cores and things 
> on all manner of Xilinx eval boards.
And also for Altera (for example, the Terasic DE2-115 with a Cyclone IV) 
and others. I've seen you int that list :) An I've seen implementations 
for smaller FPGAs like the Spatarn 6LX25
>
>
> RTEMS wise... It's pretty well supported by the community, it's open 
> source, it does all the stuff you want a RTOS to do.  it's NOT a 
> multitasking, dynamic loading OS like Linux.  That is it doesn't 
> support an MMU and process space isolation (although that might be 
> possible in newer versions.. there's a lot of configurability).  It's 
> basically a statically linked single task with threads.  They've got 
> RAM (and disk) file systems, IP stacks, a shell, YAFFS, etc.
>
> Like all open source, there's quite a lot of interesting stuff 
> available (not from rtems.org, but others) that is 90% complete.  
> Somebody at Google Summer of Code or for their Masters decides to 
> implement something cool, and gets most of the way done, then wanders 
> away (the summer ended, they got their degree, the usual story).
>
> But there's also a core of users who are serious and rigorous and 
> contribute back, so the main stuff in the distribution from Joel 
> Sherrill at OAR (who make RTEMS) is pretty rock solid. 
I will learn more about RTEMS. For the application I've (and this links 
directly to the message from Javier Serrano), the hardware platform is 
one of the CERN Open Hardware ones, the SPEC. For the purpose and 
interface needs, really an operating system is not required (no 
filesystem, no TCP/IP needed, no multitasking, no framebuffer...), and 
certainly a Linux would have a very large footprint without providing 
any real help. And about the processor selection, the trade-off that 
Javier exposes are the same I'm confronting. Both are open-sourced and 
well supported, and in one side the LM32 is smaller, in the other the 
LEON3 has more capabilities that can be implemented or not (like MMU or 
FPU, and better multi-core support, although not currently needed in my 
project). I probably will take the LEON3 road, but also because it is 
more popular in my current field, but for now I usually do not need the 
FT version since I'm more related with GSEs.
>
>
> ESA has several rigorously verified flight qualified versions of RTEMS 
> (in Portugal and Austria, as I recall)
>
Yes, this is one of the reasons to gain experience in that road :) I 
have some tendency to stay in Linux because I'm very familiarized with 
it in the non-MMU implementations (for Blackfin) and also with MMU - and 
I've found that for a small embedded system, to have the MMU is not so 
important, even sometimes it is a drawback.

In any case we are running a bit OT (except considering that this 
general discussion has timing applications, of course ;) ). Also I'm 
happy to have found a time-nut colleage in other list, and probably I 
will ask you some things about off-list in order to not increase noise, 
if possible.

Best regards,

Javier