Raspberrypi3: AUX Uart driver
Niteesh
gsnb.gn at gmail.com
Tue Jan 14 14:34:17 UTC 2020
On Tue, Jan 14, 2020 at 1:57 PM Christian Mauderer <
christian.mauderer at embedded-brains.de> wrote:
> On 13/01/2020 19:04, Niteesh wrote:
> > The ns16550_context already has a field named baud_divisor, so if the
> > user passes
> > value for it, then we can skip the GetBaudDivisor function and use that
> > value instead.
> >
> > Is this approach okay?
>
> Is the driver still able to handle different baud rates with this? Does
> the ioctl call for setting the baudrate work?
I didn't think about this, it won't work if we are using this method.
ns16550_set_attributes
calls ns16550_GetBaudDivisor, then I think we will have to stick with the
old method.
>
>
Best regards
>
> Christian
>
> >
> > On Mon, Jan 13, 2020 at 3:46 PM Niteesh <gsnb.gn at gmail.com
> > <mailto:gsnb.gn at gmail.com>> wrote:
> >
> > On Mon, Jan 13, 2020 at 1:38 PM Christian Mauderer
> > <christian.mauderer at embedded-brains.de
> > <mailto:christian.mauderer at embedded-brains.de>> wrote:
> >
> > On 12/01/2020 21:26, Niteesh wrote:
> > > On Sun, Jan 12, 2020 at 11:42 PM Christian Mauderer
> > <list at c-mauderer.de <mailto:list at c-mauderer.de>
> > > <mailto:list at c-mauderer.de <mailto:list at c-mauderer.de>>>
> wrote:
> > >
> > > Hello Niteesh,
> > >
> > > On 12/01/2020 16:06, Niteesh wrote:
> > > > The only issue, I faced while using this driver is the
> > baud divisor is
> > > > calculated
> > > > by CLOCK_FREQ/(BAUD_RATE * 16) (*ns16550-context.c:68)*
> > > > but it should BAUD_DIV = (CLOCK_FREQ/(8 * BAUD_RATE)) -
> > 1, for Rpi3.
> > > > For testing, I assigned the baud divisor to 270 (115200
> > bits/s) in
> > > > ns16550-context.c,
> > > > and everything works fine.
> > >
> > > Sounds great. In NS16550_GetBaudDivisor there is already a
> > case where
> > > the baudDivisor is calculated differently (depending on
> > > ctx->has_precision_clock_synthesizer and
> > > ctx->has_fractional_divider_register). If none of the two
> > cases are ok
> > > for the controller you could just add another one.
> > >
> > > Can we pass in a function, which gets called, won't this be
> more
> > > flexible? because
> > > in the future if we have some other board that has a different
> > > calculation for the baud rate
> > > the function will take care of it.
> >
> > It's possible. Please make sure to be compatible with the
> > current API.
> > For example if the pointer is NULL you should call the legacy
> > function
> > instead.
> >
> >
> > I will be adding an extra field, a function pointer to
> ns16550_context,
> > the prototype of the function would be *uint32_t
> > calculate_baud_divisor( ns16550_context * )*
> > This is will calculate the baud divisor using its own formula and
> > the initial baud.
> > If this function is not NULL then it would be called inside
> > *NS16550_GetBaudDivisor* function,
> > *
> > *
> >
> > >
> > > >
> > > > For console selection, my plan is to search for the aux
> > node using
> > > > compatible
> > > > property and if its status is enabled, then initialize
> > the AUX
> > > uart and
> > > > set the BSP_output_char
> > > > to aux_output_char, else pl011_output_char. All this
> > will be done
> > > inside
> > > > the uart_probe function,
> > > > except for the initialization of AUX which will be done
> in
> > > init_ctx_aux.
> > > > And finally, call the output char
> > > > function using *BSP_output_char. Do you have any neat
> > way to do this?
> > >
> > > I don't have an example for a similar case at hand. So:
> > No, no neat way
> > > that I can tell you.
> > >
> > > Before you start to write code: Please take a look at the
> > different
> > > beagle variants what is possible. Is there a variant where
> > AUX uart
> > > would be there but shouldn't be used as a console (one of
> > the Zeros
> > > maybe or the compute module?). How does Raspbian or
> > FreeBSD decide which
> > > port should be used? Maybe they decide based on the
> > commandline.txt? In
> > > such a case it would be better to just initialize all
> > active (in the
> > > fdt) serial ports and decide based on the commandline too.
> > >
> > >
> > > The Documentation says the following:
> > > *By default, on Raspberry Pis equipped with the
> > wireless/Bluetooth*
> > > *module (Raspberry Pi 3 and Raspberry Pi Zero W), **the PL011
> > UART is*
> > > *connected to the Bluetooth module, while the mini UART is
> > used as the
> > > primary UART and*
> > > *will have a Linux console on it. On all other models, the
> > PL011 is used
> > > as the primary UART.
> > >
> > > *
> > > *In Linux device terms, by default, /dev/ttyS0 refers to the
> > mini UART,
> > > and /dev/ttyAMA0 refers*
> > > *to the PL011. The primary UART is the one assigned to the
> Linux
> > > console, which depends on*
> > > *the Raspberry Pi model as described above. There are also
> > symlinks:
> > > /dev/serial0, which always*
> > > *refers to the primary UART (if enabled), and /dev/serial1,
> which
> > > similarly always refers to the secondary UART (if enabled).*
> > > *
> > > *
> > > I checked in all the DTB files, by decompiling them (files are
> > > from https://github.com/raspberrypi/firmware/tree/master/boot
> ).
> > > In all board with support for wireless and bluetooth, the AuX
> > is enabled
> > > and serial0 points to it. So we could use serial0
> > > to find the correct UART port. I think this is solid enough.
> > So, should
> > > I use this approach?
> >
> > Sounds OK. If possible please initialize the other UART too if
> it is
> > enabled in the FDT. Although we don't support bluetooth yet
> > maybe there
> > will be support in the future or someone wants to do it in the
> > application.
> >
> > I will go with this method then.
> >
> > >
> > > Or if using the command line, then we need to move the link to
> > > CONSOLE_DEVICE to console_initialize, and parse the
> > > command line twice. If this is no problem, then we could use
> this
> > > approach also.
> >
> > Would be possible too.
> >
> > >
> > > >
> > > > And why don't we have a function similar
> > to *of_device_is_available*,
> > > > since there will be more and more
> > > > FDT based boards, this will be really helpful.
> > >
> > > I agree that it would be helpful. Seems that you just
> > found a function
> > > that should be in a FDT framework.
> > >
> > > RTEMS currently only has the basic libfdt functions and
> > some RTEMS
> > > specific ones. The of_... functions belong to the FreeBSD
> > "Open Firmware
> > > Bus" which is an abstraction layer on top of FDT. It would
> > be great to
> > > identify useful ones and port them or provide an RTEMS
> > implementation.
> > > Like already discussed this could be part of a GSoC
> project.
> > >
> > > Best regards
> > >
> > > Christian
> > >
> > > >
> > > > On Sun, Jan 5, 2020 at 12:57 AM Christian Mauderer
> > > <list at c-mauderer.de <mailto:list at c-mauderer.de>
> > <mailto:list at c-mauderer.de <mailto:list at c-mauderer.de>>
> > > > <mailto:list at c-mauderer.de <mailto:list at c-mauderer.de>
> > <mailto:list at c-mauderer.de <mailto:list at c-mauderer.de>>>> wrote:
> > > >
> > > > On 04/01/2020 09:32, Niteesh wrote:
> > > > > We could now run RTEMS on Rpi3. I tried examples
> > from the
> > > samples
> > > > > section and they run
> > > > > fine. But still, a lot of functionality has to
> > tested since it
> > > > uses the
> > > > > RPI2 BSP. To test these examples
> > > > > I used a simple driver for the AUX.
> > > > > The documentation from BCM link
> > > > >
> > > >
> > >
> > <
> https://www.raspberrypi.org/app/uploads/2012/02/BCM2835-ARM-Peripherals.pdf
> > (pg
> > > > > no 10) states that
> > > > >
> > > > >
> > > > > *The implemented UART is not a 16650
> > compatible UART However
> > > > as far
> > > > > as possible the first 8 control and status
> > registers are
> > > laid out
> > > > > like a 16550 UART.*
> > > >
> > > > It also tells
> > > >
> > > > "Al 16550 register bits which are not supported
> > can be
> > > written but
> > > > will be ignored and read back as 0. All control bits
> for
> > > simple UART
> > > > receive/transmit operations are available."
> > > >
> > > > So I would expect that not everything works like
> > expected (for
> > > example
> > > > setting DCD, DSR, DTR, RI - they are not there for
> > the mini
> > > UART) but
> > > > the basic stuff should work.
> > > >
> > > > >
> > > > >
> > > > > My question is can we use the existing ns16550
> > driver or
> > > should I
> > > > create
> > > > > a new one? I also checked the address of the
> > registers the
> > > offsets
> > > > don't
> > > > > seem right to me, but someone should check and
> > correct me if
> > > I am
> > > > wrong.
> > > >
> > > > If you compare the registers in the existing driver
> > > > (NS16550_RECEIVE_BUFFER, ... in ns16550_p.h) and the
> > one in
> > > the BCM
> > > > datasheet the registers look very similar (at least
> > from the
> > > position /
> > > > function). I haven't done a bit by bit comparison
> > yet. Please
> > > note that
> > > > you have to do a conversion between the defines and
> > register
> > > addresses.
> > > > The define gives you a register index for a 32bit
> > register. So
> > > you have
> > > > to multiply by 4 to get an address. The driver is
> > designed
> > > that you
> > > > provide a setRegister and getRegister function that
> > can do this
> > > > conversion.
> > > >
> > > > Where did you find differences?
> > > >
> > > > I would suggest to just try the driver.
> > > >
> > >
> > >
> > > _______________________________________________
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> > > http://lists.rtems.org/mailman/listinfo/devel
> > >
> >
> > --
> > --------------------------------------------
> > embedded brains GmbH
> > Herr Christian Mauderer
> > Dornierstr. 4
> > D-82178 Puchheim
> > Germany
> > email: christian.mauderer at embedded-brains.de
> > <mailto:christian.mauderer at embedded-brains.de>
> > Phone: +49-89-18 94 741 - 18
> > Fax: +49-89-18 94 741 - 08
> > PGP: Public key available on request.
> >
> > Diese Nachricht ist keine geschäftliche Mitteilung im Sinne des
> > EHUG.
> >
>
> --
> --------------------------------------------
> embedded brains GmbH
> Herr Christian Mauderer
> Dornierstr. 4
> D-82178 Puchheim
> Germany
> email: christian.mauderer at embedded-brains.de
> Phone: +49-89-18 94 741 - 18
> Fax: +49-89-18 94 741 - 08
> PGP: Public key available on request.
>
> Diese Nachricht ist keine geschäftliche Mitteilung im Sinne des EHUG.
>
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