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Re: [Discuss-gnuradio] [GSoC] Co-Processors Update #9

From: Philip Balister
Subject: Re: [Discuss-gnuradio] [GSoC] Co-Processors Update #9
Date: Mon, 11 Aug 2014 14:06:10 -0400
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.7.0

On 08/11/2014 01:42 PM, Tom Tsou wrote:
> On Mon, Aug 11, 2014 at 10:06 AM, Philip Balister <address@hidden> wrote:
>> On 08/08/2014 11:54 PM, Alfredo Muniz wrote:
>>> Plan for GNU Radio:
>>> - From my talks with Pendlum, I think this approach will work for both Zynq
>>> and Keystone and any device that has shared memory with the coprocessors.
>> I doubt depending on contiguous memory will ever work for GNU Radio.
>> I've heard a lot of talk about changing the guts of GNU Radio, but no
>> real action. Especially given GNU Radios dependence on double mapped
>> buffering to handle wrap around. For things with hard IP blocks like
>> Keystone, this may be a difficult problem. Unless the IP blocks can be
>> configured to operate on non-contiguous blocks. FPGA code should be
>> written to avoid dependencies on specific buffer layouts. (Yes, I know I
>> have made this mistake, but I ahve seen the error of my ways)
> The typical use case for the TCP is variable length packets up to a
> fixed maximum (6144 bits for LTE). Message passing is inherently a
> better fit and the double-mapped buffer probably shouldn't apply. Each
> block of (soft) bits going in/out of the TCP would be contiguous, but
> subsequent chunks of memory carrying different block segments need not
> be.
>> I understand why TI drives you towards the CMEM driver, but that is a
>> lousy long term plan. They are just reusing code from prior generations
>> of drivers. And I do want to see something work so we can evaluate the
>> hard IP based GNU Radio block. My concern with your wording is that
>> people might think depending contiguous memory buffers is a good idea.
> At least from a high level, a message queue with a rotating set of
> buffer pointers seems OK to me. Though, not being familiar with the
> current Keystone transport options, what are the other preferred
> approaches?

These are good points. To date, we think of co processors accelerating
traditional signal processing operations, not operations on functions
that are better treated as message queues.

If there was more time left in GSoC, I'd ask Alfredo to look into this
line of thought :)


>   -TT

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