Raspberrypi3: Mini UART driver
Christian Mauderer
list at c-mauderer.de
Fri Dec 27 09:30:22 UTC 2019
On 27/12/2019 09:30, Niteesh wrote:
> On Fri, Dec 27, 2019 at 1:59 AM Christian Mauderer <list at c-mauderer.de
> <mailto:list at c-mauderer.de>> wrote:
>
> On 25/12/2019 15:32, Niteesh wrote:
> > What about the framebuffer it still uses minor and major's?
>
> I'm not entirely sure but I don't think that it is a problem to mix
> legacy and new style drivers.
>
> I want to create rtems_termios_device_handler for the framebuffer, the
> current driver uses console_fns and
> the functions have the old signatures, which uses major and minor
> numbers, but the device handler uses the newer interface
>
> staticboolmy_driver_first_open(
>
> rtems_termios_tty *tty,
> rtems_termios_device_context *base,
> struct termios *term,
> rtems_libio_open_close_args_t *args
> )
>
> as mentioned in the doc will it cause any trouble?
I wouldn't expect trouble.
> If it does then will
> also have to rewrite the fb right?
You should only have to touch the bsps/arm/raspberrypi/console/fbcons.c
file which is a very simple one. I don't expect that you have to touch
any other file.
>
>
>
> >
> > On Wed, Dec 25, 2019 at 3:20 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:
> >
> > 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.
> >
> > 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;
> > +
> > 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);
> > }
> >
> > -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;
> > + }
> > }
> >
> > -static int usart_last_close(int major, int minor, void *arg)
> > +static int usart_last_close(
> > + 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);
> > +
> > + 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>
> > <mailto: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>
> > <mailto: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>
> > <mailto: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>
> <mailto: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>>
> > > <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:
> > >
> > > 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>>
> > <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,
> > >
> > > 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>>>
> > > > <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:
> > > >
> > > > 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>>>
> > > > <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:
> > > >
> > > > 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>>>
> > > <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:
> > > >
> > > > 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>>>>
> > > > >
> <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
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> <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>>
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> > <mailto:list at c-mauderer.de
> <mailto:list at c-mauderer.de> <mailto:list at c-mauderer.de
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> > > <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
> <mailto:list at c-mauderer.de>>
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> <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
> > > > > >
> > > > >
> > > > >
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