RTEMS BSD Net on Atmel SAM Board

[Sebastian Huber]

On 06/06/16 10:36, Pavel Pisa wrote:
> Hello Isaac,
>
> On Thursday 02 of June 2016 17:09:31 Isaac Gutekunst wrote:
>> On 06/01/2016 07:18 PM, Pavel Pisa wrote:
>>> Hello Isaac,
>>>
>>> On Wednesday 01 of June 2016 23:09:39 Isaac Gutekunst wrote:
>>>> I believe I solved all my problems. Not enough memory. After updating
>>>> the linker script to use SDRAM, everything appears to be working well!
>>>> (Knock on wood).
>>> I think that SAM V71 setup with 2 MB of external SDRAM is not much
>>> above minimal limit for use of RTEMS with BSD networking.
>>> If the single chip solution with only 128kB of internal SRAM
>>> is considered (may be with additional 128kB which can be borrow
>>> for some buffer from the instruction TCM) then it cannot
>>> be used with libBSD based networking. So it would worth
>>> to consider lwIP. I hope that it would be integrated to
>>> the RTEMS file operations API as part of this year GSoC.
>>> So this option worth to be considered to support
>>> networking on the small systems.
>> Hi Pavel,
>>
>> Thanks for the info.
>>
>> We will definitely be adding the largest SDRAM chip we can find to our
>> final board, so I imagine we will be okay.
>>
>> Based on the weirdness I've experienced, not having enough RAM doesn't
>> necessarily result in a nice error message. What do you think is a good
>> amount of RAM to give the stack, and how can I be sure it's enough?
> I have no experience with libBSD on RTEMS. But I would expect that
> mentioned 2 MB are minimum for stack of this level/complexity.
> When I compare that with Linux then 8 MB SDRAM has been successfully
> used in many wireles routers etc. It has been minimum and I consider
> that it is not enough for latest kernel versions and full GLibC.
> Then 32 MB is OK for Linux.
>
> I expect that 8 MB should be OK for RTEMS and libBSD but some
> statistic about amount of allocated memory for example for
> 4 and 10 TCP/IP connections from Chris or Sebastian would
> be interresting. From my experience with LPC, we have
> found that 512 kB of Flash is too small for complete
> system code+initialization data if we want full RTEMS
> support for networking (TCP, TFTP, remote shell)
> even if we have 32 MB of external SDRAM.
> 1 MB of Flash should be enough for reasonable size application.
> 2 MB even for larger application.
>
> As for classical RTEMS stack, it has lower memory demand
> then libBSD, so I expect that 2 MB would be probably OK.
>
> As for lwIP, we have some experience with TMS570.
> 1 or 2 MB of Flash is OK. 256 kB of internal SRAM
> is OK for something like 4 to 10 TCP/IP connections.

If you want to go below 8MiB for the network stack, then you need fine 
tuning, e.g. of socket buffers, interface queues, etc. For this you have 
to know how the FreeBSD network stack works in detail. In addition an an 
SMP machine you need considerably more memory due to the per-processor 
UMA caches.

-- 
Sebastian Huber, embedded brains GmbH

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