<div dir="ltr"><div dir="ltr">On Mon, Jan 13, 2020 at 1:38 PM Christian Mauderer <<a href="mailto:christian.mauderer@embedded-brains.de">christian.mauderer@embedded-brains.de</a>> wrote:<br></div><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">On 12/01/2020 21:26, Niteesh wrote:<br>
> On Sun, Jan 12, 2020 at 11:42 PM Christian Mauderer <<a href="mailto:list@c-mauderer.de" target="_blank">list@c-mauderer.de</a><br>
> <mailto:<a href="mailto:list@c-mauderer.de" target="_blank">list@c-mauderer.de</a>>> wrote:<br>
> <br>
> Hello Niteesh,<br>
> <br>
> On 12/01/2020 16:06, Niteesh wrote:<br>
> > The only issue, I faced while using this driver is the baud divisor is<br>
> > calculated <br>
> > by CLOCK_FREQ/(BAUD_RATE * 16) (*ns16550-context.c:68)*<br>
> > but it should BAUD_DIV = (CLOCK_FREQ/(8 * BAUD_RATE)) - 1, for Rpi3.<br>
> > For testing, I assigned the baud divisor to 270 (115200 bits/s) in<br>
> > ns16550-context.c,<br>
> > and everything works fine.<br>
> <br>
> Sounds great. In NS16550_GetBaudDivisor there is already a case where<br>
> the baudDivisor is calculated differently (depending on<br>
> ctx->has_precision_clock_synthesizer and<br>
> ctx->has_fractional_divider_register). If none of the two cases are ok<br>
> for the controller you could just add another one.<br>
> <br>
> Can we pass in a function, which gets called, won't this be more<br>
> flexible? because<br>
> in the future if we have some other board that has a different<br>
> calculation for the baud rate<br>
> the function will take care of it.<br>
<br>
It's possible. Please make sure to be compatible with the current API.<br>
For example if the pointer is NULL you should call the legacy function<br>
instead.<br></blockquote><div> </div><div>I will be adding an extra field, a function pointer to ns16550_context,</div><div>the prototype of the function would be <b>uint32_t calculate_baud_divisor( ns16550_context * )</b></div><div>This is will calculate the baud divisor using its own formula and the initial baud.</div><div>If this function is not NULL then it would be called inside <b>NS16550_GetBaudDivisor</b> function,</div><div><b><br></b></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
> <br>
> ><br>
> > For console selection, my plan is to search for the aux node using<br>
> > compatible<br>
> > property and if its status is enabled, then initialize the AUX<br>
> uart and<br>
> > set the BSP_output_char<br>
> > to aux_output_char, else pl011_output_char. All this will be done<br>
> inside<br>
> > the uart_probe function,<br>
> > except for the initialization of AUX which will be done in<br>
> init_ctx_aux.<br>
> > And finally, call the output char<br>
> > function using *BSP_output_char. Do you have any neat way to do this?<br>
> <br>
> I don't have an example for a similar case at hand. So: No, no neat way<br>
> that I can tell you.<br>
> <br>
> Before you start to write code: Please take a look at the different<br>
> beagle variants what is possible. Is there a variant where AUX uart<br>
> would be there but shouldn't be used as a console (one of the Zeros<br>
> maybe or the compute module?). How does Raspbian or FreeBSD decide which<br>
> port should be used? Maybe they decide based on the commandline.txt? In<br>
> such a case it would be better to just initialize all active (in the<br>
> fdt) serial ports and decide based on the commandline too.<br>
> <br>
> <br>
> The Documentation says the following: <br>
> *By default, on Raspberry Pis equipped with the wireless/Bluetooth*<br>
> *module (Raspberry Pi 3 and Raspberry Pi Zero W), **the PL011 UART is*<br>
> *connected to the Bluetooth module, while the mini UART is used as the<br>
> primary UART and*<br>
> *will have a Linux console on it. On all other models, the PL011 is used<br>
> as the primary UART.<br>
> <br>
> *<br>
> *In Linux device terms, by default, /dev/ttyS0 refers to the mini UART,<br>
> and /dev/ttyAMA0 refers*<br>
> *to the PL011. The primary UART is the one assigned to the Linux<br>
> console, which depends on*<br>
> *the Raspberry Pi model as described above. There are also symlinks:<br>
> /dev/serial0, which always*<br>
> *refers to the primary UART (if enabled), and /dev/serial1, which<br>
> similarly always refers to the secondary UART (if enabled).*<br>
> *<br>
> *<br>
> I checked in all the DTB files, by decompiling them (files are<br>
> from <a href="https://github.com/raspberrypi/firmware/tree/master/boot" rel="noreferrer" target="_blank">https://github.com/raspberrypi/firmware/tree/master/boot</a>).<br>
> In all board with support for wireless and bluetooth, the AuX is enabled<br>
> and serial0 points to it. So we could use serial0<br>
> to find the correct UART port. I think this is solid enough. So, should<br>
> I use this approach?<br>
<br>
Sounds OK. If possible please initialize the other UART too if it is<br>
enabled in the FDT. Although we don't support bluetooth yet maybe there<br>
will be support in the future or someone wants to do it in the application.<br></blockquote><div>I will go with this method then. </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
> <br>
> Or if using the command line, then we need to move the link to<br>
> CONSOLE_DEVICE to console_initialize, and parse the<br>
> command line twice. If this is no problem, then we could use this<br>
> approach also.<br>
<br>
Would be possible too.<br>
<br>
> <br>
> ><br>
> > And why don't we have a function similar to *of_device_is_available*,<br>
> > since there will be more and more<br>
> > FDT based boards, this will be really helpful.<br>
> <br>
> I agree that it would be helpful. Seems that you just found a function<br>
> that should be in a FDT framework.<br>
> <br>
> RTEMS currently only has the basic libfdt functions and some RTEMS<br>
> specific ones. The of_... functions belong to the FreeBSD "Open Firmware<br>
> Bus" which is an abstraction layer on top of FDT. It would be great to<br>
> identify useful ones and port them or provide an RTEMS implementation.<br>
> Like already discussed this could be part of a GSoC project.<br>
> <br>
> Best regards<br>
> <br>
> Christian<br>
> <br>
> ><br>
> > On Sun, Jan 5, 2020 at 12:57 AM Christian Mauderer<br>
> <<a href="mailto:list@c-mauderer.de" target="_blank">list@c-mauderer.de</a> <mailto:<a href="mailto:list@c-mauderer.de" target="_blank">list@c-mauderer.de</a>><br>
> > <mailto:<a href="mailto:list@c-mauderer.de" target="_blank">list@c-mauderer.de</a> <mailto:<a href="mailto:list@c-mauderer.de" target="_blank">list@c-mauderer.de</a>>>> wrote:<br>
> ><br>
> > On 04/01/2020 09:32, Niteesh wrote:<br>
> > > We could now run RTEMS on Rpi3. I tried examples from the<br>
> samples<br>
> > > section and they run<br>
> > > fine. But still, a lot of functionality has to tested since it<br>
> > uses the<br>
> > > RPI2 BSP. To test these examples<br>
> > > I used a simple driver for the AUX.<br>
> > > The documentation from BCM link<br>
> > ><br>
> > <br>
> <<a href="https://www.raspberrypi.org/app/uploads/2012/02/BCM2835-ARM-Peripherals.pdf" rel="noreferrer" target="_blank">https://www.raspberrypi.org/app/uploads/2012/02/BCM2835-ARM-Peripherals.pdf</a>> (pg<br>
> > > no 10) states that<br>
> > > <br>
> > ><br>
> > > *The implemented UART is not a 16650 compatible UART However<br>
> > as far<br>
> > > as possible the first 8 control and status registers are<br>
> laid out<br>
> > > like a 16550 UART.*<br>
> ><br>
> > It also tells<br>
> ><br>
> > "Al 16550 register bits which are not supported can be<br>
> written but<br>
> > will be ignored and read back as 0. All control bits for<br>
> simple UART<br>
> > receive/transmit operations are available."<br>
> ><br>
> > So I would expect that not everything works like expected (for<br>
> example<br>
> > setting DCD, DSR, DTR, RI - they are not there for the mini<br>
> UART) but<br>
> > the basic stuff should work.<br>
> ><br>
> > ><br>
> > ><br>
> > > My question is can we use the existing ns16550 driver or<br>
> should I<br>
> > create<br>
> > > a new one? I also checked the address of the registers the<br>
> offsets<br>
> > don't<br>
> > > seem right to me, but someone should check and correct me if<br>
> I am<br>
> > wrong. <br>
> ><br>
> > If you compare the registers in the existing driver<br>
> > (NS16550_RECEIVE_BUFFER, ... in ns16550_p.h) and the one in<br>
> the BCM<br>
> > datasheet the registers look very similar (at least from the<br>
> position /<br>
> > function). I haven't done a bit by bit comparison yet. Please<br>
> note that<br>
> > you have to do a conversion between the defines and register<br>
> addresses.<br>
> > The define gives you a register index for a 32bit register. So<br>
> you have<br>
> > to multiply by 4 to get an address. The driver is designed<br>
> that you<br>
> > provide a setRegister and getRegister function that can do this<br>
> > conversion.<br>
> ><br>
> > Where did you find differences?<br>
> ><br>
> > I would suggest to just try the driver.<br>
> ><br>
> <br>
> <br>
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> <br>
<br>
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</blockquote></div></div>