Raspberrypi3: Mini UART driver

Christian Mauderer list at c-mauderer.de
Thu Dec 26 20:28:14 UTC 2019


Hello Niteesh,

sorry for not answering earlier. During this time of the year you have
to expect some delays on the mailing list due to public holydays and
vacations.

On 25/12/2019 10:50, Niteesh wrote:
> Just to make sure I am going in the right track.
> I moved the uart register definitions to bsp/usart.h into a struct of
> uint32_t called usart0_regs
> here is git diff of usart.c after changing it to the latest console
> interface.

Do you have a plan how you want to test these changes?

The direction looks OK. Some notes below.

By the way: Maybe it would be a better idea to just remove it completely
and use the bsps/arm/shared/serial/arm-pl011.c driver instead? That
reduces the ammount of code and therefore ammount of bugs we have in
this BSP.

> 
> diff --git a/bsps/arm/raspberrypi/console/usart.c
> b/bsps/arm/raspberrypi/console/usart.c
> index 25fb523621..b12f375a1c 100644
> --- a/bsps/arm/raspberrypi/console/usart.c
> +++ b/bsps/arm/raspberrypi/console/usart.c
> @@ -47,6 +47,12 @@ static uint32_t usart_get_baud(const console_tbl *ct)
>  }
>  #endif
>  
> +typedef struct {
> +  rtems_termios_device_context base;
> +  const char *device_name;
> +  volatile usart0_regs *regs;
> +}uart0_context;

Why uart0_context and not usart_context? All other names in this file
are called usart_...

> +
>  static void usart_set_baud(int minor, int baud)
>  {
>   /*
> @@ -55,10 +61,17 @@ static void usart_set_baud(int minor, int baud)
>   return;
>  }
>  
> -static void usart_initialize(int minor)
> +static volatile usart0_regs
> *rpi_uart_get_regs(rtems_termios_device_context *base)
>  {
> -  unsigned int gpio_reg;
> +  uart0_context *ctx;
> +
> +  ctx = (usart0_regs *) base;
> +  return ctx->regs;
> +}
>  
> +static void usart_initialize(rtems_termios_device_context *base)
> +{
> +  unsigned int gpio_reg;
>    /*
>    ** Program GPIO pins for UART 0
>    */
> @@ -75,67 +88,81 @@ static void usart_initialize(int minor)
>    usart_delay(150);
>    BCM2835_REG(BCM2835_GPIO_GPPUDCLK0) = 0;
>  
> +  volatile uint32_t *uart_regs = rpi_uart_get_regs(base);
> +
>    /*
>    ** Init the PL011 UART
>    */
> -  BCM2835_REG(BCM2835_UART0_CR)   = 0;
> -  BCM2835_REG(BCM2835_UART0_ICR)  = 0x7FF;
> -  BCM2835_REG(BCM2835_UART0_IMSC) = 0;
> -  BCM2835_REG(BCM2835_UART0_IBRD) = 1;
> -  BCM2835_REG(BCM2835_UART0_FBRD) = 40;
> -  BCM2835_REG(BCM2835_UART0_LCRH) = 0x70;
> -  BCM2835_REG(BCM2835_UART0_RSRECR) =  0;
> -
> -  BCM2835_REG(BCM2835_UART0_CR)   = 0x301;
> -
> -  BCM2835_REG(BCM2835_UART0_IMSC) = BCM2835_UART0_IMSC_RX;
> -
> -  usart_set_baud(minor, 115000);
> +  uart_regs->cr  = 0;
> +  uart_regs->icr = 0x7ff;
> +  uart_regs->imsc = 0;
> +  uart_regs->ibrd = 1;
> +  uart_regs->fbrd= 40;
> +  uart_regs->lcrh= 0x70;
> +  uart_regs->rsrecr= 0;
> +  uart_regs->cr = 0x301;
> +  uart_regs->imsc = BCM2835_UART0_IMSC_RX;
> +  // usart_set_baud(minor, 115000);

Why is this line commented now?

>  }
>  
> -static int usart_first_open(int major, int minor, void *arg)
> +static bool usart_first_open(
> +  rtems_termios_tty *tty,
> +  rtems_termios_device_context *base,
> +  struct termios *term,
> +  rtems_libio_open_close_args_t *args
> +)
>  {
> -  rtems_libio_open_close_args_t *oc = (rtems_libio_open_close_args_t *)
> arg;
> -  struct rtems_termios_tty *tty = (struct rtems_termios_tty *)
> oc->iop->data1;
> -  const console_tbl *ct = Console_Port_Tbl [minor];
> -  console_data *cd = &Console_Port_Data [minor];
> +  rtems_status_code sc;
> +  uart0_context *ctx;
> +  bool ok;
>  
> -  cd->termios_data = tty;
> -  rtems_termios_set_initial_baud(tty, ct->ulClock);
> +  ctx = (uart0_context *) base;
>  
> -  return 0;
> +  usart_initialize(base);
> +
> +  sc = rtems_termios_set_initial_baud(tty,  USART0_DEFAULT_BAUD);
> +  if ( sc != RTEMS_SUCCESSFUL ){
> +    printk("Error setting the baud for termios\n");
> +    return false;
> +  }

There is a return missing here. Did you compile the code? The compiler
should give you a warning about that.

>  }
>  
> -static int usart_last_close(int major, int minor, void *arg)
> +static int usart_last_close(

The first_open returns a bool but last_close returns still an int? Is
this correct? I don't have the interface memorized.

> +  rtems_termios_tty *tty,
> +  rtems_termios_device_context *base,
> +  rtems_termios_open_close_args_t *arg)
>  {
>    return 0;
>  }
>  
> -static int usart_read_polled(int minor)
> +static int usart_read_polled(rtems_termios_device_context *base)
>  {
> -  if (minor == 0) {
> -    if (((BCM2835_REG(BCM2835_UART0_FR)) & BCM2835_UART0_FR_RXFE) == 0) {
> -       return((BCM2835_REG(BCM2835_UART0_DR)) & 0xFF );
> -    } else {
> -      return -1;
> -    }
> -  } else {
> -    printk("Unknown console minor number: %d\n", minor);
> -    return -1;
> +  volatile usart0_regs *regs;
> +
> +  regs = rpi_uart_get_regs(base);

Just noted that here: Why rpi_uart_get_regs and not usart_get_regs?
Please use a consitent naming scheme.

> +
> +  if ((regs->fr & BCM2835_UART0_FR_RXFE) == 0) {
> +    return (regs->dr & 0xFF);
>    }
> +
> +  return -1;
>  }
>  
> -static void usart_write_polled(int minor, char c)
> +static void usart_write_polled(rtems_termios_device_context *base, char c)
>  {
> -   while (1) {
> -     if ((BCM2835_REG(BCM2835_UART0_FR) & BCM2835_UART0_FR_TXFF) == 0)
> -       break;
> -   }
> -   BCM2835_REG(BCM2835_UART0_DR) = c;
> +  volatile usart0_regs *regs;
> +
> +  regs = rpi_uart_get_regs(base);
> +
> +  while (1) {
> +    if (((regs->fr) & BCM2835_UART0_FR_TXFF) == 0)
> +      break;
> +  }
> +  regs->dr = c;
>  }
>  
>  static ssize_t usart_write_support_polled(
> -  int minor,
> +  rtems_termios_device_context *base,
>    const char *s,
>    size_t n
>  )
> @@ -143,7 +170,7 @@ static ssize_t usart_write_support_polled(
>    ssize_t i = 0;
>  
>    for (i = 0; i < n; ++i) {
> -    usart_write_polled(minor, s [i]);
> +    usart_write_polled(base, s[i]);
>    }
>  
>    return n;
> @@ -154,14 +181,11 @@ static int usart_set_attributes(int minor, const
> struct termios *term)
>    return -1;
>  }
>  
> -const console_fns bcm2835_usart_fns = {
> -  .deviceProbe = libchip_serial_default_probe,
> -  .deviceFirstOpen = usart_first_open,
> -  .deviceLastClose = usart_last_close,
> -  .deviceRead = usart_read_polled,
> -  .deviceWrite = usart_write_support_polled,
> -  .deviceInitialize = usart_initialize,
> -  .deviceWritePolled = usart_write_polled,
> -  .deviceSetAttributes = usart_set_attributes,
> -  .deviceOutputUsesInterrupts = false
> -};
> +const rtems_termios_device_handler bcm2835_uart0_handler_polled = {
> +  .first_open = usart_first_open,
> +  .last_close = usart_last_close,
> +  .poll_read = usart_read_polled,
> +  .set_attributes = usart_set_attributes,
> +  .write = usart_write_support_polled,
> +  .mode = TERMIOS_POLLED
> +}
> \ No newline at end of file
> 
> On Wed, Dec 25, 2019 at 12:36 AM Joel Sherrill <joel at rtems.org
> <mailto:joel at rtems.org>> wrote:
> 
> 
> 
>     On Tue, Dec 24, 2019, 12:19 PM Niteesh <gsnb.gn at gmail.com
>     <mailto:gsnb.gn at gmail.com>> wrote:
> 
>         And also the register definitions are in raspberrpi.h file
>         should I move them to usart.h.
> 
> 
>     Sounds right if you mean bsp/usart.h
> 
>         I have a doubt we have a register field in device_context
>         typedef struct { 
> 
>             rtems_termios_device_context base; 
> 
>             const char *device_name; 
> 
>             volatile some_chip_registers *regs;
> 
>         } my_driver_context;
> 
>         How does the reg field point to the correct memory location? for
>         instance in IMX BSP,
>         there is a struct with register field's but none of the define a
>         memory location?
> 
> 
>     Make sure the structure has volatiles and proper alignment. :)
> 
> 
>         On Tue, Dec 24, 2019 at 11:37 PM Niteesh <gsnb.gn at gmail.com
>         <mailto:gsnb.gn at gmail.com>> wrote:
> 
>             How to handle different serial devices? In other BSPs the
>             uart devices are the same, so
>             they were able to put it under a single array? But here we
>             have 2 uarts and a FB?
> 
> 
>             On Tue, Dec 24, 2019 at 8:18 PM Christian Mauderer
>             <list at c-mauderer.de <mailto:list at c-mauderer.de>> wrote:
> 
>                 On 24/12/2019 12:06, Niteesh wrote:
>                 > The current raspi console section is like this:
>                 > The bsp_console_select in console_select.c is
>                 responsible for selecting
>                 > between uart and the framebuffer. It does so
>                 > by setting the Console_port_minor.
>                 > The console_config is responsible for output_char
>                 function.
>                 > And other files are driver code.
>                 > If rewriting, this would be my approach,
>                 > Rewrite the bsp_console_select to set some kind of a
>                 variable like in
>                 > IMX, then in console_initialize function
>                 > link the right driver to /dev/console.
>                 > Replace the console_tbl with the device_context and
>                 console_fns with
>                 > termios_device_handlers and
>                 > finally add in the console_initialization function.
> 
>                 I agree that this would be a clean solution. So if you
>                 want you can do
>                 that. But there might is a hurdle: As far as I
>                 understood you you only
>                 have a Pi3? So you might have a hard time testing the
>                 changes. Maybe the
>                 simulator could work.
> 
>                 Another possibility could be to set the
>                 "Console_port_minor" to
>                 something unused (for example -1). In that case you can
>                 define another
>                 /dev/console.
> 
>                 Best regards and merry Christmas (in case you celebrate)
> 
>                 Christian
> 
>                 >
>                 > On Tue, Dec 24, 2019 at 2:13 PM Niteesh
>                 <gsnb.gn at gmail.com <mailto:gsnb.gn at gmail.com>
>                 > <mailto:gsnb.gn at gmail.com <mailto:gsnb.gn at gmail.com>>>
>                 wrote:
>                 >
>                 >     Thank you so much, for such a detailed answer. Now
>                 things make
>                 >     really good sense to me, 
>                 >     going through the code now is just a breeze. But I
>                 still have one
>                 >     question
>                 >     for the newer driver interface is
>                 console_initialize the function
>                 >     which RTEMS calls while initializing
>                 >     the console? Which means I can't mess with the
>                 name right? It is
>                 >     similar to the main function, right?
>                 >
>                 >     The current driver is a legacy one, how do you
>                 want me to proceed,
>                 >     shall I rewrite the legacy to a
>                 >     the new one, this is will be a great
>                 learning experience for me also
>                 >     and we also get the BSP updated to the latest
>                 interface.
>                 >
>                 >
>                 >     On Tue, Dec 24, 2019 at 3:20 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>>>
>                 wrote:
>                 >
>                 >         Hello Niteesh,
>                 >
>                 >         quite a lot of questions. I'll try to answer
>                 them. Note that it
>                 >         has been
>                 >         some time since I had a detailed look at that
>                 code so if something I
>                 >         tell seems odd please don't hesitate to
>                 question it.
>                 >
>                 >         Please note that in RTEMS their are more or
>                 less two "levels" of
>                 >         support
>                 >         for a serial console:
>                 >
>                 >         1. A very basic polled system console (also
>                 known as
>                 >         "debug-console" in
>                 >         some BSPs). This one is used for printk and
>                 should work in basically
>                 >         every case. It is used for critical system
>                 messages like
>                 >         printing the
>                 >         exception frame. For that a BSP has to provide a
>                 >         "BSP_output_char" function.
>                 >
>                 >         2. A full featured UART driver integrated into
>                 Termios. That one
>                 >         will be
>                 >         used for all normal I/O on the UARTs.
>                 >
>                 >         As far as I know the "console_tbl
>                 Console_Configuration_Ports"
>                 >         belongs
>                 >         to a table based legacy interface. It is
>                 handled in the file
>                 >         bsps/shared/dev/serial/legacy-console.c. I'm
>                 not sure whether it is
>                 >         documented in the BSP guide because it
>                 shouldn't be used for new
>                 >         BSPs.
>                 >         Same is true for the "major" and "minor"
>                 stuff: It's not really
>                 >         used for
>                 >         new drivers.
>                 >
>                 >         Newer drivers use the initialization that is
>                 described in the manual
>                 >         that you have already found. Basically they use
>                 >         "rtems_termios_device_install" to register a
>                 new UART as
>                 >         "/dev/ttySomething". Some recent (ARM) BSPs
>                 that do that are the
>                 >         imx or
>                 >         the atsam.
>                 >
>                 >         The console that is used for stdin, stdout and
>                 stderr (printf,
>                 >         scanf,
>                 >         ...) is the one called "/dev/console" (defined in
>                 >         CONSOLE_DEVICE_NAME).
>                 >         For the legacy table based interface it's the
>                 one with the index of
>                 >         "Console_Port_Minor".
>                 >
>                 >
>                 >         If you want to access any UART other than the
>                 one for stdin and
>                 >         stdout
>                 >         you do that the same way like on Linux: Just
>                 use the "open"
>                 >         function on
>                 >         the "/dev/ttySomething" and use "read",
>                 "write" and simmilar or use
>                 >         "fopen" together with "fread", "fwrite",
>                 "fprintf", ...
>                 >
>                 >
>                 >         "printf" (and family) is a function belonging
>                 to the C library.
>                 >         In our
>                 >         case that's newlib. It will format your
>                 message and after some other
>                 >         preprocessing will call the "write" function
>                 of the file that is
>                 >         opened
>                 >         as stdout (which is "/dev/console" in the
>                 default case).
>                 >
>                 >
>                 >         I hope that I helped you with that
>                 explanation. Please feel free
>                 >         to ask
>                 >         anything if it isn't clear.
>                 >
>                 >         Best regards
>                 >
>                 >         Christian
>                 >
>                 >         On 23/12/2019 19:50, Niteesh wrote:
>                 >         > And finally, how does printf work? It is a
>                 macro? In that
>                 >         case, how does
>                 >         > any write to
>                 >         > a console work?
>                 >         >
>                 >         > On Tue, Dec 24, 2019 at 12:18 AM Niteesh
>                 <gsnb.gn at gmail.com <mailto:gsnb.gn at gmail.com>
>                 >         <mailto:gsnb.gn at gmail.com
>                 <mailto:gsnb.gn at gmail.com>>
>                 >         > <mailto:gsnb.gn at gmail.com
>                 <mailto:gsnb.gn at gmail.com> <mailto:gsnb.gn at gmail.com
>                 <mailto:gsnb.gn at gmail.com>>>> wrote:
>                 >         >
>                 >         >     Is the correct port minor number set
>                 during the
>                 >         initialization? What
>                 >         >     is the application want's to
>                 >         >     access some other port?
>                 >         >
>                 >         >     On Tue, Dec 24, 2019 at 12:16 AM Niteesh
>                 >         <gsnb.gn at gmail.com <mailto:gsnb.gn at gmail.com>
>                 <mailto:gsnb.gn at gmail.com <mailto:gsnb.gn at gmail.com>>
>                 >         >     <mailto:gsnb.gn at gmail.com
>                 <mailto:gsnb.gn at gmail.com> <mailto:gsnb.gn at gmail.com
>                 <mailto:gsnb.gn at gmail.com>>>> wrote:
>                 >         >
>                 >         >         I would like to clarify my doubts
>                 regarding the
>                 >         console driver.
>                 >         >         I went through the documentation
>                 >         >         for the console
>                 >         >       
>                 >       
>                   driver https://docs.rtems.org/branches/master/bsp-howto/console.html#introduction.
>                 >         >         But it is quite different from how
>                 some BSPs initialize.
>                 >         >         Correct me if I am wrong
>                 >         >         The console_tbl contains the various
>                 entries of serial
>                 >         ports.
>                 >         >         The console_fns is a struct of
>                 function pointers,
>                 >         which point to
>                 >         >         the BSP uart functions.
>                 >         >         The BSP_output_char_function_type is
>                 what will be
>                 >         called for
>                 >         >         printing a char on to the console.
>                 >         >         How does RTEMS initialize the uart?
>                 It's seems not to
>                 >         be same
>                 >         >         for all BSPs.
>                 >         >         The doc says that the driver's
>                 initialization function
>                 >         is called
>                 >         >         once during the rtems initialization
>                 process.
>                 >         >         The console init function install
>                 the serial driver using
>                 >         >         rtems_termios_device_install but
>                 there seems to be
>                 >         >         no such function in the raspberry
>                 pi? But there is a
>                 >         entry in
>                 >         >         console_fns for init function, but
>                 then how does it
>                 >         >         gets called?
>                 >         >         And for BSP's with multiple
>                 serial's, the output function
>                 >         >         chooses the right serial using
>                 console_port_minor,
>                 >         >         Is it during initialization?
>                 >         >         What is the need for get and set
>                 register functions? 
>                 >         >
>                 >         >         On Mon, Dec 23, 2019 at 1:04 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 22/12/2019 19:45, Joel
>                 Sherrill wrote:
>                 >         >             >
>                 >         >             >
>                 >         >             > On Sun, Dec 22, 2019, 12:29 PM
>                 Niteesh
>                 >         <gsnb.gn at gmail.com <mailto:gsnb.gn at gmail.com>
>                 <mailto:gsnb.gn at gmail.com <mailto:gsnb.gn at gmail.com>>
>                 >         >             <mailto:gsnb.gn at gmail.com
>                 <mailto:gsnb.gn at gmail.com> <mailto:gsnb.gn at gmail.com
>                 <mailto:gsnb.gn at gmail.com>>>
>                 >         >             > <mailto:gsnb.gn at gmail.com
>                 <mailto:gsnb.gn at gmail.com>
>                 >         <mailto:gsnb.gn at gmail.com
>                 <mailto:gsnb.gn at gmail.com>> <mailto:gsnb.gn at gmail.com
>                 <mailto:gsnb.gn at gmail.com>
>                 >         <mailto:gsnb.gn at gmail.com
>                 <mailto:gsnb.gn at gmail.com>>>>> wrote:
>                 >         >             >
>                 >         >             >     On Sun, Dec 22, 2019 at
>                 8:44 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>> <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
>                 <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:
>                 >         >             >
>                 >         >             >         Hello Niteesh,
>                 >         >             >
>                 >         >             >         thanks for doing that
>                 work.
>                 >         >             >
>                 >         >             >         On 22/12/2019 12:10,
>                 Niteesh wrote:
>                 >         >             >         > The rpi1 and rpi2
>                 use the PL011 UART,
>                 >         whereas,
>                 >         >             with RPI's
>                 >         >             >         equipped with
>                 >         >             >         > wireless/Bluetooth
>                 module, the PL011 is
>                 >         >             connected to the Bluetooth
>                 >         >             >         > module, and the mini
>                 UART is used as
>                 >         the primary
>                 >         >             UART.
>                 >         >             >
>                 >         >             >         In my opinion it would
>                 be great if you
>                 >         could use
>                 >         >             the FDT to
>                 >         >             >         distinguish
>                 >         >             >         between the boards.
>                 That should allow to add
>                 >         >             raspberry 3 (and
>                 >         >             >         maybe 4)
>                 >         >             >         support without adding
>                 another BSP. More
>                 >         BSPs mean
>                 >         >             a bigger
>                 >         >             >         maintenance
>                 >         >             >         effort for the RTEMS
>                 community.
>                 >         >             >
>                 >         >             >     Learning more about FDT is
>                 on my list for a long
>                 >         >             time.  I would love
>                 >         >             >     to work on that
>                 >         >             >     but I have almost no exp
>                 with FDT's.
>                 >         >             >     But another thing could
>                 also be done, in
>                 >         >             >   
>                  raspberrypi/start/bspstart.c we get the
>                 >         revision and
>                 >         >             >     model of the board using
>                 the mailbox. Every
>                 >         board has
>                 >         >             a unique id,
>                 >         >             >     which we could use to
>                 initialize
>                 >         >             >     the BSP. But using FDT
>                 seems to be a more
>                 >         elegant
>                 >         >             option, it is a
>                 >         >             >     lot of work I think, but
>                 we could take
>                 >         >             >     help from libbsd and linux
>                 I suppose. What
>                 >         do you think?
>                 >         >             >
>                 >         >             >
>                 >         >             > I think there are almost
>                 always two steps to a
>                 >         project
>                 >         >             like this: get it
>                 >         >             > to work and make it nice. :)
>                 >         >             >
>                 >         >             > If you fix the startup code to
>                 read the board
>                 >         revision and
>                 >         >             memory size,
>                 >         >             > you can get a working BSP that
>                 dynamically
>                 >         adapts to the
>                 >         >             models and
>                 >         >             > memory variations with minimal
>                 modifications. If
>                 >         you want
>                 >         >             to then
>                 >         >             > convert the BSP to FDT, it
>                 will be a LOT easier
>                 >         to debug
>                 >         >             with a working BSP.
>                 >         >             >
>                 >         >             > Plus you may be able to
>                 identify every variation
>                 >         point
>                 >         >             based on just the
>                 >         >             > model info. Then FDT is just a
>                 matter of
>                 >         switching the
>                 >         >             source of
>                 >         >             > some/all of the info.
>                 >         >             >
>                 >         >             > That would be my work plan anyway.
>                 >         >
>                 >         >             I agree with Joel that a secure
>                 development basis
>                 >         (also
>                 >         >             known as "hack")
>                 >         >             as a first step is a good idea.
>                 You maybe even
>                 >         just make the
>                 >         >             mini UART
>                 >         >             the default driver while you are
>                 developing. Then
>                 >         you can be
>                 >         >             sure that
>                 >         >             you have the right driver.
>                 >         >
>                 >         >             As soon as that works you can
>                 either change to the
>                 >         revision
>                 >         >             method or
>                 >         >             (better) to the FDT one and
>                 after that the patches
>                 >         can be
>                 >         >             merged. Using
>                 >         >             the FDT isn't that complicated.
>                 Basically you
>                 >         search for a
>                 >         >             node based on
>                 >         >             different parameters. For an
>                 example you can take
>                 >         a look at
>                 >         >             the imx BSP.
>                 >         >             In imx_uart_probe
>                 >         (bsps/arm/imx/console/console-config.c) a
>                 >         >             fdt node is
>                 >         >             searched and based on that a
>                 UART driver is used.
>                 >         But again:
>                 >         >             Follow
>                 >         >             Joels suggestion to start simple
>                 and secure.
>                 >         >
>                 >         >             >
>                 >         >             >         >
>                 >         >             >         >
>                 >         >             >       
>                 >         >           
>                 >       
>                    https://www.raspberrypi.org/app/uploads/2012/02/BCM2835-ARM-Peripherals.pdf
>                 >         >             >         > But from the above
>                 doc (PAGE 10), the
>                 >         mini uart
>                 >         >             has 16550 like
>                 >         >             >         registers
>                 >         >             >         > and RTEMS already
>                 has the driver for it
>                 >         >             >         >
>                 bsps/shared/dev/serial/ns16550.c. But
>                 >         I am not
>                 >         >             sure how
>                 >         >             >         compatible they
>                 >         >             >         > are? Should a new
>                 driver be
>                 >         implemented from
>                 >         >             scratch or use
>                 >         >             >         ns16550 if
>                 >         >             >         > possible?
>                 >         >             >
>                 >         >             >         In general it's better
>                 to re-use
>                 >         existing code.
>                 >         >             That has multiple
>                 >         >             >         advantages:
>                 >         >             >
>                 >         >             >         - It reduces the
>                 maintenance effort.
>                 >         Fewer code
>                 >         >             means fewer work.
>                 >         >             >         - If you have multiple
>                 driver for the
>                 >         same or
>                 >         >             similar hardware
>                 >         >             >         it can
>                 >         >             >         happen that a bug is
>                 fixed in one but
>                 >         not the other.
>                 >         >             >         - It's simpler to find
>                 a hardware to
>                 >         test changes.
>                 >         >             >         - The driver becomes
>                 more universal with
>                 >         every new
>                 >         >             supported
>                 >         >             >         hardware.
>                 >         >             >         That increases the
>                 chance that it fits
>                 >         the next
>                 >         >             new hardware.
>                 >         >             >
>                 >         >             >         I'm sure there are
>                 some more if you ask
>                 >         someone else.
>                 >         >             >
>                 >         >             >     I do understand the
>                 issues, I just spent
>                 >         some time
>                 >         >             reading the
>                 >         >             >     driver code.
>                 >         >             >     I think we could most
>                 probably use it. I
>                 >         will take a
>                 >         >             closer look and
>                 >         >             >     will update.
>                 >         >             >
>                 >         >
>                 >         >             Great.
>                 >         >
>                 >         >             >          
>                 >         >             >
>                 >         >             >         >
>                 >         >             >         > Also, the core clock
>                 on which the
>                 >         PL011 is based
>                 >         >             on is changed
>                 >         >             >         in rpi3.
>                 >         >             >         > Rpi1 and 2 use
>                 250Mhz as the default
>                 >         clock but
>                 >         >             it was changed
>                 >         >             >         to 400Mhz
>                 >         >             >         > in Rpi3 and newer
>                 >         >             >
>                 >         >             >         Again: Would be great
>                 if that could be
>                 >         adapted
>                 >         >             based on FDT or by
>                 >         >             >         reading the right
>                 registers.
>                 >         >             >
>                 >         >             >         >
>                 >         >             >         > Few differences
>                 between PL011 and Mini
>                 >         uart
>                 >         >             >         > The mini UART has
>                 smaller FIFOs.
>                 >         Combined with
>                 >         >             the lack of
>                 >         >             >         flow control,
>                 >         >             >         > this makes it more
>                 prone to losing
>                 >         characters at
>                 >         >             higher baud
>                 >         >             >         rates. It
>                 >         >             >         > is also generally
>                 less capable than
>                 >         the PL011,
>                 >         >             mainly due to
>                 >         >             >         its baud
>                 >         >             >         > rate link to the VPU
>                 clock speed.
>                 >         >             >
>                 >         >             >         That shouldn't really
>                 be a problem for
>                 >         the system
>                 >         >             console.
>                 >         >             >
>                 >         >             >         >
>                 >         >             >         > The particular
>                 deficiencies of the
>                 >         mini UART
>                 >         >             compared to the
>                 >         >             >         PL011 are :
>                 >         >             >         >
>                 >         >             >         > No break detection
>                 >         >             >         > No framing errors
>                 detection
>                 >         >             >         > No parity bit
>                 >         >             >         > No receive timeout
>                 interrupt
>                 >         >             >         > No DCD, DSR, DTR or
>                 RI signals
>                 >         >             >         >
>                 >         >             >
>                 >         >             >   
>                  _______________________________________________
>                 >         >             >     devel mailing list
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>                 <mailto:devel at rtems.org> <mailto:devel at rtems.org
>                 <mailto:devel at rtems.org>>
>                 >         <mailto:devel at rtems.org
>                 <mailto:devel at rtems.org> <mailto:devel at rtems.org
>                 <mailto:devel at rtems.org>>>
>                 >         >             <mailto:devel at rtems.org
>                 <mailto:devel at rtems.org> <mailto:devel at rtems.org
>                 <mailto:devel at rtems.org>>
>                 >         <mailto:devel at rtems.org
>                 <mailto:devel at rtems.org> <mailto:devel at rtems.org
>                 <mailto:devel at rtems.org>>>>
>                 >         >             >   
>                  http://lists.rtems.org/mailman/listinfo/devel
>                 >         >             >
>                 >         >
>                 >
> 


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