GSoC 2015: Raspberry Pi 2 Support

[Joel Sherrill]

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