[Buildroot] How is the RM9200 status of buildroot ?

Jorge S. jorgesolla at gmail.com
Mon Jan 14 16:50:23 UTC 2008

Ulf, thanks for your interesting reply.

On Jan 12, 2008 5:19 PM, Ulf Samuelsson <ulf at atmel.com> wrote:

>  Hi All,
>  I've had some bad expecirences using the AT91RM9200 on a custom board:
>  1) Unable to boot from parallel flash, so you have to use an external
> eeprom if you want to use a parallel flash
>    or end up using an SPI Dataflash as i did (see problem 2)
> ==> That is a misunderstanding of the datasheet.
>        You can boot from a 16 bit parallel flash, if BMS is low.
>        If BMS is high (and the internal bootROM is used) the part
>        will not find any parallel flash.
>        Both the AT91RM9200DK and AT91RM9200EK boot from parallel flash.

Of course, you are right, i didnt mean "no parallel flash" at all.

>  2) When using SPI Dataflash on CS0 you have to use the bit-bang kernel
> driver instead of the SPI hardware, because of
>     another problem on the CS that can cause random operations on the
> dataflash and end up ruining your filesystem.
>     There's no clear workaround for this problem, some say it works when
> slowing down the SPI, some other say that it
>     still fails even when its running slow, and so on.
> ==> The problem is that if the PDC (DMA) does not get any cycles,
>        NPCS0 will go high until the PDC has made its memory access,
>        breaking a transfer into two, causing confusion at the other end of
> the SPI.
>        The workaround is to either reduce the speed to < 5 Mbps
>        or ensure that the NPCS0 remains low by using external glue logic.
>        The speed reduction needs to be done in all parts of the system,
>        I.E: dataflashboot, U-boot and linux.

Maybe its my fault here, but i didn't success when trying to slow down the
SPI speed, i modified my custom board definition
file on the kernel, but it doesn't work, it always says "5Mbps". I've also
received feedback from people who was having the same
issue that reported fails even when spi is going slower than 5Mbps.

Any example here?

>  3) I managed to get buildroot working on a JFFS2 filesystem after
> looooooooots of problems with the default atmel configs, so
>     i did my own config.
> ==> If you find a problem, it makes sense to feed them back.

I did on the mailing list.

>  Hope this info is useful for somebody...
>  Now my questions:
>  I'm now facing a new project that requires the develpment of a new custom
> board but i don't want to use the
>  AT91RM9200 again (enough is enough) so i'm doing some investigation on
> the
> AT91SAM926x family.
>  Questions:
>    - Is buildroot working OK for the AT91SAM926x? Any 1st hand experience?
> I'm talking only about the toolchain+utilities
>          part of buildroot (i usually build kernel and u-boot appart from
> buildroot)
> ==> You can get a running toolchain.
>        A lot of the applications will build, but not all.
>        Do not expect Buildroot to build a running X-Windows.

Good news for me,  i don't need X-Windows or any gfx at the moment.

>   - The RM9200 was having an errata on the ROM bootloader not allowing you
> to boot from a parallel dataflash, according to the AT91SAM9260 datasheet,
> theres an errata on the SAM9260 too, that leads to the same
> problem...unable
> to boot from parallel flash. So the only workaround i see is to use a SPI
> dataflash to boot, and an additional parallel flash for the rootfs (i need
> more than 8MiB).
> ==> The AT91SAM9260 rev A, will not be able to boot from NAND flash.
>        You can boot from SPI dataflash or external parallel flash.
>        As in the RM9200, you have to pull BMS low to boot from the par
> flash.
>        There is no S/W support from Atmel for boot from parallel flash
> yet.
>        I hope it will be there during mid spring.
>        Still a lot of customers are using parallel flash with the part
> using
>        the normal flash support in U-boot.

Nah, nevermind, dataflash  is  cheap,  i can afford a dataflash+NAND combo,
i choose the easy way.

>  - (Maybe this is a kernel-list question) Again, based on experience... Do
> you guys know if the kernel is supporting "well" the main peripherals?
>   or are there any "pending" issues related to hardware erratas? I need
> SPI, I2C, USB (host), Ethernet and maybe some GPIO pins that look like
> supported when taking a look at the kernel patches... any useful "warning"
> here? I don't want to face again the same problems on the RM9200 :(.
> ==> USB host - OK.
>        Ethernet - Use internal SRAM for buffers, if you plan to strangle
> the bus
>        with 16 bit operation or run the bus at slow speed.
>        SPI:    The AT91RM9200 problem is gone.
>                   At high speeds, you can get a problem with SPI overruns
> on receive.
>                   I have seen this at customers when the SPI is using 60%
> of the available
>                   bandwidth on the bus.
>                   Often, an SPI transfer is only using data in a single
> direction, and if you do an SPI read,
>                    then it might be good to get the send data from the
> internal SRAM.
>                    If you do an SPI send, then it might make sense to
> write the data to
>                    an internal part of the chip (like "/dev/null"),
> instead of writing to the
>                    SDRAM and then discarding it.
>                  There is a discussion going on at this point of time, and
>                  you should check out the ARM linux mailing list.
>        I2C, The jury is still out on this, and some get it to work and
> some doesn't.
>                The vanilla driver is polling the I2C and this could cause
> problems.
>                I have customers using interrupt driven I2C and they say
>                that they do not have any issues.
>        - Any "cheap" development board, like the KB920x for the
> AT91RM9200?
> ==> If you start a development now, then you may want to consider getting
>        the AT91SAM9260A (or AT91SAM9G20 as will be its new name)
>        Pin compatible, 400 MHz, and will have larger FIFO for Ethernet.
>        There is one less USART and one more I2C.
> ==> Check out www.olimex.com

Board ordered,  that's  what  i was looking for! ,  thanks again  Ulf,  i
really appreciate  your  help.

And , another question: Any working OEM wifi (802.11x) for the AT91SAM?  I
know i can use USB (i did it on the RM9200 board), but i think usb is not
really an industrial solution, i need something "hardwired" on the PCB.

Thank you again, your support is really helpful.
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