Raspberry Pi test report
Alan Cudmore
alan.cudmore at gmail.com
Wed Jan 8 15:26:05 UTC 2020
The Debian Linux variant for the Raspberry Pi (Raspbian) is still 32 bit
for both the Pi 3 and 4, so I would think 32 bit ports would run on both.
The Raspberry Pi 4 has a Quad Core A72, 1 to 4 Gigabytes of LPDDR4 SDRAM,
Gigabit ethernet, USB 3, Wi-fi and bluetooth. I have not looked into it
enough to see what UARTs it uses.
On Wed, Jan 8, 2020 at 1:18 AM Christian Mauderer <
christian.mauderer at embedded-brains.de> wrote:
> On 08/01/2020 00:24, Joel Sherrill wrote:
> >
> >
> > On Tue, Jan 7, 2020 at 12:42 PM Christian Mauderer <list at c-mauderer.de
> > <mailto:list at c-mauderer.de>> wrote:
> >
> > Hello Alan,
> >
> > I pushed the patches mentioned further below. So the raspberry BSP
> > should now work again for all raspberry 1 and 2 on the official
> master
> > branch. Note that the
> >
> > kernel_address=0x200000
> >
> > is still necessary.
> >
> >
> > This is awesome work. What about the Pi 3 and and Pi 4? I think Niteesh
> > has the Pi 3 working so that leaves the 4. Any idea?
> >
> > --joel
> >
>
> As far as I followed his work Niteesh had some minimal version working
> with the mini UART and thought about trying the existing NS16550 (after
> I suggested that one). But I haven't seen a patch yet. So currently even
> if some basic stuff runs there will be no console.
>
> Beneath that: Pi 3 and Pi 4 are both 64Bit cores. I don't have any
> experience with aarch64. Therefore I'm not sure whether we can safely
> use them with 32Bit fallback. It seems to work to some extend but
> according to
>
> https://en.wikipedia.org/wiki/ARM_architecture#AArch64
>
> "ARMv8-A allows 32-bit applications to be executed in
> a 64-bit OS, and a 32-bit OS to be under the control
> of a 64-bit hypervisor."
>
> So I'm not sure in which situations we will run into problems. Maybe on
> interrupts?
>
> Best regards
>
> Christian
>
> >
> > Best regards
> >
> > Christian
> >
> > On 06/01/2020 11:10, Christian Mauderer wrote:
> > > Hello Alan,
> > >
> > > thanks for your very detailed tests.
> > >
> > > On 05/01/2020 23:42, Alan Cudmore wrote:
> > >> I finally found the time to try the latest RTEMS head on my
> > collection
> > >> of Raspberry Pi models.
> > >> The last time I tried to run RTEMS on a Pi, I had trouble with the
> > >> current version of the Raspberry Pi Firmware, so I had to go back
> > to a
> > >> specific tag on the Rasberry Pi firmware repository to get RTEMS
> to
> > >> work. This time, the head of the firmware repository seems to
> > work (at
> > >> least on the single core models)
> > >>
> > >> To keep things simple, I'm just going address the single core
> models
> > >> here, I can follow up after I finish testing the Raspberry Pi 2.
> > >>
> > >> Test Setup:
> > >> I used the git.rtems.org <http://git.rtems.org>
> > <http://git.rtems.org> rtems master from Jan 03
> > >> 2020.
> > >> I used the Raspberry Pi firmware from the same date.
> > >> The firmware can be found here:
> > >> https://github.com/raspberrypi/firmware/tree/master/boot
> > >> To boot an RTEMS image, you can copy all files from the above
> "boot"
> > >> directory on a DOS formatted SD/MicroSD card along with the RTEMS
> > image
> > >> (more about that in a minute).
> > >> On the SD card, I deleted the "dtb" files, as well as the overlay
> > >> directory. I dont think these are necessary to boot an RTEMS
> image.
> > >>
> > >> I built a new arm-rtems5 toolchain using the RSB tool (head from
> the
> > >> same date) and built the "raspberrypi" BSP. After a quick test
> > failed, I
> > >> reviewed the latest mailing list posts, and ended up applying the
> > linker
> > >> script patch:
> > >> https://lists.rtems.org/pipermail/devel/2019-December/056551.html
> > >
> > > I don't think that we will apply that patch. It moves code in an
> area
> > > that is protected against access to catch null pointer accesses
> later.
> > > This increases the image size.
> > >
> > > The alternative is to add the line
> > >
> > > kernel_address=0x200000
> > >
> > > to the config.txt of the raspberry SD image. Niteesh is in the
> process
> > > of documenting this:
> > >
> > >
> https://lists.rtems.org/pipermail/devel/2020-January/056796.html
> > >
> > >>
> > >> After applying this patch and rebuilding, a few RTEMS samples
> > seemed to
> > >> work fine on the Raspberry Pi Zero Models 1.2 and 1.3 (no
> > wireless). I
> > >> ran hello.exe, ticker.exe, and unlimited.exe
> > >>
> > >> The above images must be prepared using the following command:
> > >> $ arm-rtems5-objcopy -Obinary ticker.exe kernel.img
> > >> Then I copied kernel.img over the linux kernel on the SD card.
> > >>
> > >> For all of these tests, I found this serial to USB board to be
> very
> > >> useful in my tests:
> > >> https://www.adafruit.com/product/3589
> > >> It can power the pi through the USB cable and has a power switch
> > as well.
> > >>
> > >> After the Pi Zero models, I tried my remaining older single core
> > models:
> > >> 1. Raspberry Pi Model B ( Original single core model with 512MB
> > of RAM
> > >> and 26 pin GPIO header)
> > >> 2. Raspberry Pi Model B+ (Updated Single core model with 512MB of
> RAM
> > >> and 40 pin GPIO header)
> > >> 3. Raspberry Pi Model A+ (Smaller form factor single core model
> with
> > >> 256MB of RAM and 40 pin GPIO header)
> > >> (Note this model has been updated to now have 512MB of RAM)
> > >>
> > >> All three of the above models had the same exception that has been
> > >> discussed on the mailing list:
> > >> https://lists.rtems.org/pipermail/devel/2019-December/056556.html
> > >
> > > I addressed that issue in the following patch set:
> > >
> > >
> https://lists.rtems.org/pipermail/devel/2019-December/056623.html
> > >
> https://lists.rtems.org/pipermail/devel/2019-December/056622.html
> > >
> https://lists.rtems.org/pipermail/devel/2019-December/056624.html
> > >
> > > I'll push it in the next days together with patches regarding the
> > > console from Niteesh. I just gave it some more time for review
> during
> > > the public holidays.
> > >
> > > Basically it addresses the issues that you describe below.
> > >
> > >>
> > >> All of these single core models are supposed to be compatible, and
> > >> should run the same RTEMS image given the same memory
> configuration.
> > >> Since the previous message was discussing the bspgetworkarea.c
> > changes,
> > >> I made a couple of changes:
> > >> - Reverted to the generic bspgetworkarea.c file, and changed the
> > memory
> > >> size from 256MB to 128MB ( same as the 4.11 release ).
> > >> With these changes, the same RTEMS images worked on all single
> > core models:
> > >> - RPi Zero 1.2 and 1.3
> > >> - RPi Model B
> > >> - RPi Model B+
> > >> - RPi Model A+
> > >>
> > >> Findings:
> > >> 1. The code that identifies the models in bspstart.c does not
> account
> > >> for the older models:
> > >>
> >
> https://git.rtems.org/rtems/tree/bsps/arm/raspberrypi/start/bspstart.c
> > >> The RPi Model B, B+, and A+ that I have all use the older
> > revision which
> > >> is not in the table in bspstart.c. I think we can fix this by
> > adding the
> > >> older revision codes in the table, but I think this code is
> > mostly cosmetic.
> > >>
> >
> https://www.raspberrypi.org/documentation/hardware/raspberrypi/revision-codes/README.md
> > >>
> > >> 2. I think the code that determines the memory size in
> > bspgetworkarea.c
> > >> is not correct:
> > >>
> >
> https://git.rtems.org/rtems/tree/bsps/arm/raspberrypi/start/bspgetworkarea.c
> > >> a) The mask for the memory size field should probably be 0x7
> > rather
> > >> than 0xf. The 0xF picks up the "new revision" field of the word.
> > >>
> > >>
> >
> https://git.rtems.org/rtems/tree/bsps/arm/raspberrypi/start/bspgetworkarea.c#n70
> > >> b) I'm not sure if the rpi_mem array is correct. The values
> > are used
> > >> in address size calculations, but the values seem to be in
> Kilobytes,
> > >> not Megabytes. Maybe I'm not catching a shift that is done on
> > these values.
> > >>
> > >>
> >
> https://git.rtems.org/rtems/tree/bsps/arm/raspberrypi/start/bspgetworkarea.c#n73
> > >> c) I'm not sure that the numbers all add up. Line 80 computes
> the
> > >> ram_end value by adding the Work Area start to the total size of
> the
> > >> RAM. I think this will overrun the end of the RAM.
> > >>
> > >>
> >
> https://git.rtems.org/rtems/tree/bsps/arm/raspberrypi/start/bspgetworkarea.c#n80
> > >> d) I would like to look at the relationship between the
> ram_end
> > >> calculation and the ram_size given in the autoconfigure setting (
> > >> currently at 256MiB). Are the MMU settings done based on the hard
> > coded
> > >> linker script value that may conflict with the sizes set here?
> > >> e) the code may not work for the older models that do not
> > have the
> > >> updated revision fields.
> > >>
> > >> If the intent is to cover the different raspberry pi memory sizes
> > >> automatically, then we can probably rework this code to work for
> > all models.
> > >> We may be able to use the following rationale to simplify the
> > memory logic:
> > >> 1. All of the current production single core raspberry Pi models
> have
> > >> 512MB of RAM. Do we need to worry about out of production 256MiB
> > models?
> > >> I have an older A+ model with 256MiB, but I am unlikely to use it
> for
> > >> anything serious. I would rather use a Raspberry Pi Zero instead.
> > Given
> > >> that, we could assume that the "raspberrypi" BSP has 512 MiB of
> RAM.
> > >> This would only require the calculation of how much memory is
> > devoted to
> > >> the GPU.
> > >>
> > >> 2. All of the Raspberry Pi 2 models have 1 Gigabyte of RAM, so the
> > >> raspberrypi2 BSP can safely assume 1 gigabyte.
> > >>
> > >> We could also use the specific revision code register (old and
> > new) to
> > >> set the RAM size, since that should be accurate.
> > >>
> > >> Anyway, that is what I have so far on the single core models. I
> would
> > >> like to take a look at the Pi 2 next. Note that the Pi 2 is a
> > Quad A7,
> > >> that is considered "legacy" but it is still in production. The
> latest
> > >> Raspberry Pi 2 has been switched to a Quad core A53, so it is now
> > very
> > >> similar to the Raspberry Pi 3 without the Wireless/Bluetooth
> > module. I
> > >> dont have a Raspberry Pi 2 with an A53.
> > >>
> > >> There are quite a few newer models as well, so it's probably
> worth a
> > >> discussion of what we really want to support. My personal
> > preferences:
> > >> - Of the single core models, I would be happy with Raspberry Pi
> Zero
> > >> (and possibly Zero W) support. These are are very inexpensive and
> > >> available worldwide. It may be the least expensive non-simulator
> > RTEMS
> > >> target board available.
> > >> - I would like one multi-core model as an inexpensive SMP target
> > to work
> > >> with and learn RTEMS SMP details. Again, my focus is on low cost
> and
> > >> wide availability.
> > >
> > > In the ideal case: All models.
> > > In the real case: It's unfunded. Therefore we take the ones that
> > someone
> > > is ready to add and maintain during free time.
> > >
> > > Beneath that I think it's more a question which models should be in
> > > which BSP variant.
> > >
> > > The `raspberry` variant uses the following CPU_CFLAGS:
> > >
> > > CPU_CFLAGS = -mcpu=arm1176jzf-s
> > >
> > > The `raspberry2` variant uses the following CPU_CFLAGS:
> > >
> > > CPU_CFLAGS = -march=armv7-a -mthumb -mfpu=neon -mfloat-abi=hard
> > > -mtune=cortex-a7
> > >
> > > Maybe we will need a variant in the future for an aarch64 support
> when
> > > the core is supported in RTEMS somewhen. Currently I hope that we
> can
> > > just fall back to 32 Bit mode for the newer models.
> > >
> > > So the variants will end up with only a different core. It should
> be
> > > possible to handle other differences by parsing the FDT. Niteesh
> > already
> > > started that with the console.
> > >
> > >>
> > >> Thanks for you attention, and happy new year!
> > >
> > > A happy new year to you too.
> > >
> > > Best regards
> > >
> > > Christian
> > >
> > >> Alan
> > >>
> > >>
> > >>
> > >> _______________________________________________
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> > >>
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> > >
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> >
> >
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>
> --
> --------------------------------------------
> embedded brains GmbH
> Herr Christian Mauderer
> Dornierstr. 4
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> Germany
> email: christian.mauderer at embedded-brains.de
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