GSoC 2015: Raspberry Pi 2 Support

[Joel Sherrill]

On June 2, 2015 7:01:21 AM EDT, Rohini Kulkarni <krohini1593 at gmail.com> wrote:
>Dr. Joel,
>
>So we can't say something solely on the basis of this result? 

I don't think so. If Linux performs the same, then what you did is as good as it gets.

However, if Linux is faster then some setting still isn't right.

You need a reference measurement to have any confidence. It is possible you did something but didn't actually turn the cache (or all the cache) on.

>On 2 Jun 2015 16:28, "Rohini Kulkarni" <krohini1593 at gmail.com> wrote:
>
>I have not run it under linux on pi2 yet. Will have to run and check
>the result. 
>
>On 2 Jun 2015 16:16, "Joel Sherrill" <joel.sherrill at oarcorp.com> wrote:
>
>
>
>On June 2, 2015 5:58:33 AM EDT, Rohini Kulkarni <krohini1593 at gmail.com>
>wrote:
>>HI,
>>
>>I tried running the dhrystone benchmark with some changes for
>cache/mmu
>>set up.
>>
>>However, the output shows a reduction in performance.
>>The time to run through the dhrystone has increased from 12 to 13 and
>>dhrystones run per second decreased.
>>
>>According to this result, things were better with caches disabled.
>>
>>
>>I have been working on this since two days and could not figure out an
>>improvement. Any pointers?
>
>How did it do under Linux on the Pi2?
>
>
>>Thanks.
>>
>>
>>
>>On Thu, May 28, 2015 at 8:41 PM, Rohini Kulkarni
>><krohini1593 at gmail.com> wrote:
>>
>>Hi All,
>>
>>I have to implement the cache coherency support for Cortex A7. But for
>>A7 MPCore, unlike for A9, I am not able to find any register
>>description for the Snoop Control Unit from the TRM.
>>
>>I need help here on how to proceed.
>>
>>Additionally for A9 there is a single bit for A9 in the Auxiliary
>>Control Register which enables cache broadcast operations. The
>register
>>format is different for A7 and again I am unable to find how to
>achieve
>>the same for A7.
>>
>>Thanks!
>>
>>
>>
>>
>>
>>On Tue, May 5, 2015 at 10:42 PM, Joel Sherrill
>><joel.sherrill at oarcorp.com> wrote:
>>
>>
>>
>>On 5/5/2015 11:11 AM, Rohini Kulkarni wrote:
>>
>>Hi,
>>
>>I am working with the code for bsp hooks. I am referring to existing
>>ARM multicore bsp codes, zync mainly.
>>
>>1. There are existing hooks for the raspberry pi. Where should the
>code
>>for the  Pi2 hooks be added?
>>
>>The Pi and Pi2 are remarkably similar so Pi2 should be placed inside
>>the Pi BSP directory.
>>There is already a Pi2 variant of that code built. But we know
>specific
>>places where there
>>are variances. Depending on the scope of what is different, it can be
>>as simple as
>>a cpp conditional in a .h to select a value or two implementations of
>a
>>single method
>>and the Makefile.am picking the right file to build based on the board
>>variant.
>>
>>The big question to always ask is: Is this specific to the Pi2 and
>>incompatible with the Pi?
>>
>>Since the Pi BSP is still missing capabilities, it is likely code
>>common to both will
>>be added this summer. For example, did the mailbox interface change? I
>>don't know
>>but would guess that it didn't.  Each new capability added needs that
>>added.
>>
>>And any differences need to be analyzed to pick the least intrusive
>way
>>to provide
>>alternate implementations. Or enable special code like the Pi2 SMP
>>support which
>>is dependent on --enable-smp and being a Pi2.
>>
>>2. Am I right in understanding that I will have to implement A7
>>specific functions as have been for A9? I am referring specifically to
>>the arm-a9mpcore-start.h
>>
>>Yes.
>>
>>If the code is very similar between the a7 and a9, then a discussion
>>on devel@ should occur to decide the best way to minimize duplication.
>>
>>If you end up with a7 specific code, you should follow the location
>and
>>
>>naming patterns already established. That places it in
>>libbsp/arm/shared/...
>>so it can be used by any BSP with the right SMP core.
>>
>>
>>I am referring to existing codes to locate and get hold of what needs
>>to be done in the hooks. However, being new to such implementations, I
>>am taking longer to understand the details. Any suggestions that might
>>help here are welcome
>>
>>The answer will depend on the factors listed above. When code can
>>be shared, we want to share it across as many BSPs as makes sense.
>>When it is unique to a specific BSP **variant** (e.g. Pi vs Pi2), then
>>you want to find the way to account for the variation in the least
>>intrusive code way possible.
>>
>>Thanks!
>>
>>On 1 May 2015 12:45, "Rohini Kulkarni" <krohini1593 at gmail.com> wrote:
>>
>>
>>Hi,
>>
>>Excited to be a part of  this edition of GSoC! Thanks to everybody for
>>helping me get here and congratulations to all the participating
>>students!
>>
>>So, now getting to work, firstly I wish to know, specifically from my
>>mentors, any changes that must be made to my proposed project or
>>schedule.
>>
>>Secondly, are there any specifics for the development blog that we
>need
>>to create for the project? Over time what is the blog expected to
>>convey.
>>
>>Also, I have to create a new wiki page for my project as none exists.
>I
>>want to know how to add one.
>>
>>--
>>
>>Rohini Kulkarni
>>
>>
>>-- Joel Sherrill, Ph.D. Director of Research & Development
>>joel.sherrill at OARcorp.com On-Line Applications Research Ask me about
>>RTEMS: a free RTOS Huntsville AL 35805 Support Available (256)
>722-9985
>>
>>
>>
>>
>>
>>--
>>
>>Rohini Kulkarni
>>
>>
>>
>>
>>--
>>
>>Rohini Kulkarni
>
>--joel

--joel