Raspberry Pi SD card support
Andre Marques
andre.lousa.marques at gmail.com
Tue Apr 22 11:06:38 UTC 2014
On 04/17/14 19:21, Alan Cudmore wrote:
> On 4/17/2014 5:42 AM, Andre Marques wrote:
>> On 04/17/14 03:22, Alan Cudmore wrote:
>>>
>>> On Wed, Apr 16, 2014 at 4:49 PM, Joel Sherrill
>>> <joel.sherrill at oarcorp.com <mailto:joel.sherrill at oarcorp.com>> wrote:
>>>
>>>
>>> On 4/16/2014 2:06 PM, Alan Cudmore wrote:
>>>>
>>>>
>>>>
>>>> On Thu, Apr 10, 2014 at 7:11 PM, Andre Marques
>>>> <andre.lousa.marques at gmail.com
>>>> <mailto:andre.lousa.marques at gmail.com>> wrote:
>>>>
>>>> On 04/04/14 20:19, Joel Sherrill wrote:
>>>>
>>>> On 4/4/2014 1:15 PM, Gedare Bloom wrote:
>>>>
>>>> The license looked fine to me.
>>>>
>>>> +1
>>>>
>>>> As always, we just need to be careful on a file per
>>>> file basis just in case
>>>> something else in rpi-boot has a different license.
>>>>
>>>>
>>>> All files in rpi-boot use a similar licence, so I will be
>>>> using some code from rpi-boot as a base for this.
>>>>
>>>>
>>>> Great.
>>>>
>>>>
>>>>
>>>> On Thu, Apr 3, 2014 at 10:06 PM, Alan Cudmore
>>>> <alan.cudmore at gmail.com
>>>> <mailto:alan.cudmore at gmail.com>> wrote:
>>>>
>>>> From my limited research, it looks like the
>>>> emmc controller in the Raspberry
>>>> Pi BCM2835 may be the way to go.
>>>> It looks like it is a high level controller for
>>>> the SD/MMC card slot on the
>>>> Pi.
>>>>
>>>> Since this is a custom controller, I don't
>>>> think there would be an existing
>>>> driver in RTEMS.
>>>>
>>>> It seems that this emmc controller in the Pi
>>>> may handle different types of
>>>> cards, and at a higher level than just using
>>>> the SPI bus to access the card.
>>>> ( This is based on some searches of
>>>> conversations on the raspberry pi forums
>>>> , not my experience )
>>>>
>>>> You would have to write a driver for this emmc
>>>> controller and provide the
>>>> interface to libblock for the file system
>>>> interface on RTEMS. The code you
>>>> have linked above for rpi-boot looks like it
>>>> has a permissive license, so it
>>>> *may* be possible to use this code in the RTEMS
>>>> driver. There is some other
>>>> potentially useful code in there too.
>>>>
>>>>
>>>> The mailbox access, mmio read and write and the timer code
>>>> will also be usefull, and not only for emmc. This timer
>>>> code differs from the misc/timer.h currently in the
>>>> raspberrypi BSP, as it waits a certain amount of time
>>>> (until some register gets updated). The misc/timer.h is a
>>>> benchmark timer, so one of them would have to be renamed or
>>>> reorganized.
>>>>
>>>>
>>>> Can an RTEMS timer be used for the mailbox communication?
>>>> Also, I don't think the benchmark timer code in the RTEMS
>>>> Raspberry Pi BSP is functional.
>>>>
>>> Do you mean rtems_timer_XXX or the timer in the BSP?
>>>
>>>
>>> I mean the rtems_timer_ api. Maybe we can use this, or other RTEMS
>>> features to implement the mailbox interface rather than just going
>>> directly to the timer hardware like we see in the "bare metal"
>>> examples.
>>
>> Maybe the "timer" concept here is a little misleading. I was talking
>> about a wait with timeout, until some register gets updated. The
>> rtems_timer api schedules a routine to be executed after some period
>> of time, but the register may (and should) be updated before the
>> timeout.
>>
>> I am not sure if this would be recommended, but using the rtems_timer
>> api a timer could be set for a period of time (the timeout), and
>> while the timer is going the driver would check if the register has
>> been updated. If so the timer would be cancelled. Is this good
>> practice with the rtems_timer api?
>
> I agree that the rtems_timer might not be the best mechanism for the
> waiting on the mailbox.
> If the CPU<->GPU interface supports interrupts, then a non-blocking
> driver could be written.
From what I understand the CPU<->GPU interface does support interrupts.
> Otherwise, what is the best approach?
> - a sleep call
> - polling a status register
>
Yes a small sleep followed by a polling on the register can be used.
> While I am on the subject of polling, I just remembered that the UART
> driver in the BSP does not support interrupts. We should look at this
> sometime too.
>
>>
>>>
>>> The timer driver in the BSP is strictly for benchmarking --
>>> nothing else. It is used
>>> by the tmtests and psxtmtests. It should not be used for any
>>> other purpose.
>>>
>>> How does the mailbox work? Describe it and we can figure out how
>>> to best address
>>> it.
>>>
>>>
>>> The mailbox is the interface between the Video Core GPU and the ARM
>>> processor on the Pi. Here are some docs:
>>> https://github.com/raspberrypi/firmware/wiki/Mailboxes
>>> https://github.com/raspberrypi/firmware/wiki/Accessing-mailboxes
>>> https://github.com/raspberrypi/firmware/wiki/Mailbox-property-interface
>>>
>>
>> The mailbox interface is a register that has several channels ("mail
>> accounts") for different resources on the board, so a driver sends a
>> buffer with a request (an "email") to one of them and gets answers.
>> This is an abstraction layer mainly usefull to communicate with the
>> GPU since its documentation isn't available (that is how I see it),
>> but can be used to get other types of information, not related with
>> the GPU.
>>
>> Any work with the GPU, however, will probably need to use this interface.
>>
>> In practice it is just a matter of dealing with reading and writting
>> to the mailbox registers, following a small protocol. This could be
>> put into the misc directory in the Raspberry Pi BSP.
>>
>> One thing I haven't found on the Raspberry Pi BSP is a memory
>> barrier. The memory mapped i/o to the registers shoud have a memory
>> barrier around the read and writes to a peripheral when more than one
>> peripheral is being used, according to the bcm2835 datasheet (page 7).
>>
>> http://www.raspberrypi.org/wp-content/uploads/2012/02/BCM2835-ARM-Peripherals.pdf
>>
> Good point. Is this memory barrier an assembly instruction? Should we
> create a couple of macros that generate the inline assembly?
>
It is an assembly instruction:
http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0360f/I1014942.html
(Data memory barrier)
There is also the need to consider an alternative to the BCM2835_REG
macro (in the raspberrypi.h header) that is being used to access
registers but with the memory barrier calling, instead of calling the
memory barrier macro every time in the code.
>
>
>>> The details of the GPU have been closed, and the linux port has
>>> relied on a binary blob for the GPU firmware, but Broadcom recently
>>> took a huge step in opening it up:
>>> http://www.raspberrypi.org/a-birthday-present-from-broadcom/
>>>
>>> Hopefully this will help improve the understanding of this interface.
>>>
>>>> I have been contacted by someone who is currently working on a
>>>> console driver for the BSP, and has been able to display fonts.
>>>> We may want to include him, because I think the graphics code
>>>> uses mailbox communication to the GPU.
>>>>
>>>> It is very interesting that the GPU is running a commercial
>>>> RTOS, and we will be communicating to it with RTEMS.
>>>>
>>> :)
>>>
>>>> My plan was to have at the root of the raspberrypi BSP a
>>>> folder "emmc" for the emmc driver code, and the mailbox,
>>>> mmio and timer on the misc folder, with the headers on the
>>>> include folder. What do you think?
>>>>
>>>> I have been trying the rpi-boot emmc code for the past
>>>> week, and I modified the hello test to use the emmc driver
>>>> (an overly simplified version of the rpi-boot, just to read
>>>> the slot info register for now), and my compilation process
>>>> has been:
>>>>
>>>> 1. Add/change files in Raspberrypi BSP
>>>> 2. Update Makefile.am
>>>> 3. Run bootstrap -p and bootstrap from the RaspberryPi BSP
>>>> folder
>>>> 4. (Re)configure RTEMS
>>>> 5. make and make install RTEMS from the root folder
>>>>
>>>> That is pretty much what I do. Although it might be possible to
>>>> test drivers and code in the RKI image, then integrate it into
>>>> the RTEMS tree when it is ready.
>>>>
>>> --enable-maintainer-mode is supposed to track regenerating the
>>> Makefile.in
>>> and configure files when you modify Makefile.am or configure.ac
>>> <http://configure.ac>.
>>>
>>> The current build system has a serious deficiency in that it
>>> does **not**
>>> track the dependency of the test executables on any .a or .h
>>> file from RTEMS.
>>> So the best solution for quick builds is usually to remove the
>>> executable you
>>> are testing and then run make.
>>>
>>> Step 3 above is the minimum for a bootstrap. bootstrap -p is
>>> only needed
>>> when you add/delete/move .h files.
>>>
>>>> I have been using the --enable-maintainer-mode, but I am
>>>> not sure about exacly what it simplifies, because I always
>>>> needed to do those steps for it to compile and link correctly.
>>>>
>>>>
>>>> I don't know what this does either..
>>>>
>>> Just tracks dependencies on generated Makefile/configure related
>>> files back
>>> to their source.
>>>
>>>>
>>>> Alan
>>>>
>>>>
>>>> --André Marques
>>>>
>>>>
>>>>
>>>> I'll have to try the serial bootloader, I am
>>>> also close to ordering an
>>>> inexpensive JTAG adapter to try loading and
>>>> debugging through JTAG. uboot is
>>>> another possibility, using a TFTP server.
>>>>
>>>> Alan
>>>>
>>>>
>>>>
>>>>
>>>> On Wed, Apr 2, 2014 at 12:02 PM, Andre Marques
>>>> <andre.lousa.marques at gmail.com
>>>> <mailto:andre.lousa.marques at gmail.com>> wrote:
>>>>
>>>> Hello,
>>>>
>>>> I'm intending to work in the SD card
>>>> support for the Raspberry Pi BSP,
>>>> using the SD mode instead of the SPI mode.
>>>>
>>>> The references I have gathered so far for
>>>> this are as follows:
>>>>
>>>> The Raspberry Pi SOC guide: Broadcom
>>>> BCM2835 Peripherals Guide (Chapter 5
>>>> - EMMC)
>>>>
>>>> The simplified SD standard -
>>>> https://www.sdcard.org/downloads/pls/simplified_specs/
>>>>
>>>> And the following github code -
>>>> https://github.com/jncronin/rpi-boot/blob/master/emmc.c
>>>>
>>>> There is also the libchip/i2c/spi-sd-card
>>>> libi2c driver, which can also be
>>>> a reference (even though it uses SPI).
>>>>
>>>> Now, the questions:
>>>>
>>>> Should I use the Generic Disk Device
>>>> driver, as the
>>>> libchip/i2c/spi-sd-card ?
>>>>
>>>> Is there any driver using the SD mode for
>>>> sd card access, or using an emmc
>>>> interface currently in the RTEMS code base?
>>>> I haven't found any.
>>>>
>>>> On a side note, I managed to send RTEMS
>>>> applications to the RPi though the
>>>> UART interface using the xmodem protocol.
>>>>
>>>> For that I used the following bootloader
>>>>
>>>> https://github.com/dwelch67/raspberrypi/tree/master/bootloader05
>>>>
>>>> It takes me 2 minutes to send 1 MB of data
>>>> to the RPi, but this could be
>>>> improved if it used 1024 byte block
>>>> transfer instead of the default of 128.
>>>> The bootloader loads the transfered program
>>>> to memory and runs it. Then the
>>>> RPi must be rebooted so a new program can
>>>> be sent.
>>>>
>>>> It may not be the best way, but only
>>>> requires an usb-to-uart cable, and
>>>> avoids the current SD card "dance" to run
>>>> programs on the Pi.
>>>>
>>>> Thank you for your time.
>>>>
>>>> --André Marques
>>>>
>>>>
>>>> _______________________________________________
>>>> rtems-devel mailing list
>>>> rtems-devel at rtems.org
>>>> <mailto:rtems-devel at rtems.org>
>>>> http://www.rtems.org/mailman/listinfo/rtems-devel
>>>>
>>>> _______________________________________________
>>>> rtems-devel mailing list
>>>> rtems-devel at rtems.org <mailto:rtems-devel at rtems.org>
>>>> http://www.rtems.org/mailman/listinfo/rtems-devel
>>>>
>>>>
>>>>
>>>
>>> --
>>> Joel Sherrill, Ph.D. Director of Research & Development
>>> joel.sherrill at OARcorp.com <mailto:joel.sherrill at OARcorp.com> On-Line Applications Research
>>> Ask me about RTEMS: a free RTOS Huntsville AL 35805
>>> Support Available(256) 722-9985 <tel:%28256%29%20722-9985>
>>>
>>>
>>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.rtems.org/pipermail/devel/attachments/20140422/2ff5c323/attachment-0001.html>
More information about the devel
mailing list