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2009-08-21 Roxana Leontie <roxana.leontie@gmail.com>

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* bsp_howto/framebuffer.t: Updated the frame buffer documentation.
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Joel Sherrill
2009-08-21 18:41:50 +00:00
parent cb09a5da6a
commit 2eb33fdcb7
2 changed files with 159 additions and 64 deletions
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doc/ChangeLog
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@@ -1,3 +1,7 @@
2009-08-21 Roxana Leontie <roxana.leontie@gmail.com>
* bsp_howto/framebuffer.t: Updated the frame buffer documentation.
2009-08-05 Joel Sherrill <joel.sherrill@OARcorp.com>
* user/conf.t: Add configuration of posix message queue file

219
doc/bsp_howto/framebuffer.t
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@@ -8,33 +8,50 @@
@chapter Frame Buffer Driver
In this chapter, we present the basic functionality implemented by a
frame buffer driver: @code{frame_buffer_initialize()}, @code{frame_buffer_open()},
@code{frame_buffer_close()}, @code{frame_buffer_read()}, @code{frame_buffer_write()}
and @code{frame_buffer_control()}.
@section Introduction
The purpose of the frame buffer driver is to provide an abstraction for the
The purpose of the frame buffer driver is to provide an abstraction for
graphics hardware.
By using the frame buffer interface the application can access the graphics
without knowing anything about the low-level communication.
By using the frame buffer interface, an application can display graphics
without knowing anything about the low-level details of interfacing to a
particular graphics adapter. The parameters governing the mapping of
memory to displayed pixels (planar or linear, bit depth, etc) is still
implementation-specific, but device-independent methods are provided to
determine and potentially modify these parameters.
The frame buffer driver is usually located in the @code{console} directory
of the BSP and registered by the name @b{/dev/fb}
The frame buffer driver is commonly located in the @code{console}
directory of the BSP and registered by the name @b{/dev/fb0}.
Additional frame buffers (if available) are named @b{/dev/fb1},
@b{/dev/fb2}, etc.
@section Driver Functioning Overview
To work with the frame buffer, the following operation sequence is used:
@code{open()}, @code{ioctls()} to get the frame buffer info, @code{read()} and/or
@code{write()}, and @code{close()}.
@section Driver Function Overview
@subsection Initialization
The driver initialization is called once during the RTEMS initialization
process and returns RTEMS_SUCCESSFUL when the device driver is successfully
initialized
initialized. During the initialization, a name is assigned to the frame
buffer device. If the graphics hardware supports console text output,
as is the case with the pc386 VGA hardware, initialization into graphics
mode may be deferred until the device is @code{open()}ed.
The @code{frame_buffer_initialize} function may look like this:
The @code{frame_buffer_initialize()} function may look like this:
@example
@group
rtems_device_driver frame_buffer_initialize(
rtems_device_major_number major,
rtems_device_minor_number minor,
void *arg
)
void *arg)
@{
rtems_status_code status;
@@ -43,12 +60,17 @@ rtems_device_driver frame_buffer_initialize(
/*
* Register the device
*/
status = rtems_io_register_name ("/dev/fb", major, 0);
status = rtems_io_register_name("/dev/fb0", major, 0);
if (status != RTEMS_SUCCESSFUL)
@{
@{
printk("Error registering frame buffer device!\n");
rtems_fatal_error_occurred( status );
@}
@}
/*
* graphics hardware initialization goes here for non-console
* devices
*/
return RTEMS_SUCCESSFUL;
@}
@@ -57,40 +79,16 @@ rtems_device_driver frame_buffer_initialize(
@subsection Opening the Frame Buffer Device
The @code{frame_buffer_open} function is called whenever a frame buffer device is opened.
The device registered as @code{"/dev/fb"} (@code{FRAMEBUFFER_DEVICE_NAME}) is
opened automatically during RTEMS initialization. For instance, if the frame buffer is
registered as "/dev/fb", the @code{frame_buffer_open} entry point will be called as the
result of an @code{open("/dev/fb", mode)} in the application.
The @code{frame_buffer_open()} function is called whenever a frame buffer device is opened.
If the frame buffer is registered as "/dev/fb0", the @code{frame_buffer_open} entry point
will be called as the result of an @code{open("/dev/fb0", mode)} in the application.
The @code{frame_buffer_open} function returns RTEMS_SUCCESSFUL when the device driver
is successfully opened:
Thread safety of the frame buffer driver is implementation-dependent.
The VGA driver shown below uses a mutex to prevent multiple open()
operations of the frame buffer device.
@example
@group
rtems_device_driver frame_buffer_open(
rtems_device_major_number major,
rtems_device_minor_number minor,
void *arg
)
@{
ega_hwinit();
printk( "frame buffer open called.\n" );
return RTEMS_SUCCESSFUL;
@}
@end group
@end example
The @code{ega_hwinit()} which takes care of the hardware initialization.
@subsection Closing the Frame Buffer Device
The @code{frame_buffer_close} is invoked when the serial device is to be closed.
This entry point corresponds to the device driver close entry point.
The @code{frame_buffer_close} function freeing up the hardware resources.
Returns RTEMS_SUCCESSFUL when the device driver is successfully closed:
The @code{frame_buffer_open()} function returns RTEMS_SUCCESSFUL when the device driver
is successfully opened, and RTEMS_UNSATISFIED if the device is already open:
@example
@group
@@ -100,9 +98,47 @@ rtems_device_driver frame_buffer_close(
void *arg
)
@{
if (pthread_mutex_unlock(&mutex) == 0)@{
/* restore previous state. for VGA this means return to text mode.
* leave out if graphics hardware has been initialized in
* frame_buffer_initialize() */
ega_hwterm();
printk( "FBVGA close called.\n" );
return RTEMS_SUCCESSFUL;
@}
return RTEMS_UNSATISFIED;
@}
@end group
@end example
In the previous example, the function @code{ega_hwinit()} takes care of
hardware-specific initialization.
@subsection Closing the Frame Buffer Device
The @code{frame_buffer_close()} is invoked when the frame buffer device
is closed. It frees up any resources allocated in
@code{frame_buffer_open()}, and should restore previous hardware state.
The entry point corresponds to the device driver close entry point.
Returns RTEMS_SUCCESSFUL when the device driver is successfully closed:
@example
@group
rtems_device_driver frame_buffer_close(
rtems_device_major_number major,
rtems_device_minor_number minor,
void *arg)
@{
pthread_mutex_unlock(&mutex);
/* TODO check mutex return value, RTEMS_UNSATISFIED if it failed. we
* don't want to unconditionally call ega_hwterm()... */
/* restore previous state. for VGA this means return to text mode.
* leave out if graphics hardware has been initialized in
* frame_buffer_initialize() */
ega_hwterm();
printk( "frame buffer close called.\n" );
return RTEMS_SUCCESSFUL;
@}
@@ -112,7 +148,11 @@ rtems_device_driver frame_buffer_close(
@subsection Reading from the Frame Buffer Device
The @code{frame_buffer_read} is invoked when the serial device is to be read from.
The @code{frame_buffer_read()} is invoked from a @code{read()} operation
on the frame buffer device.
Read functions should allow normal and partial reading at the end of frame buffer memory,
returning RTEMS_UNSATISFIED if trying to read beyond the frame buffer
memory or a negative number of bytes.
This method returns RTEMS_SUCCESSFUL when the device is successfully read from:
@example
@@ -123,17 +163,40 @@ rtems_device_driver frame_buffer_read(
void *arg
)
@{
/*TBD*/
return RTEMS_SUCCESSFUL;
/*printk( "FBVGA read called.\n" );*/
rtems_libio_rw_args_t *rw_args = (rtems_libio_rw_args_t *)arg;
if ( (rw_args->offset >= fb_fix.smem_len) || (rw_args->count < 0) )@{
return RTEMS_UNSATISFIED;
@}
else
@{
/*partial reading*/
if ( (rw_args->offset + rw_args->count) > fb_fix.smem_len )@{
rw_args->count = fb_fix.smem_len - rw_args->offset;
memcpy(rw_args->buffer, (const void *) (rw_args->offset + fb_fix.smem_start), rw_args->count);
rw_args->bytes_moved = rw_args->count;
return RTEMS_SUCCESSFUL;
@}
/*best reading case*/
else@{
memcpy(rw_args->buffer, (const void *) (rw_args->offset + fb_fix.smem_start), rw_args->count);
rw_args->bytes_moved = rw_args->count;
return RTEMS_SUCCESSFUL;
@}
@}
@}
@end group
@end example
@subsection Writing to the Frame Buffer Device
The @code{frame_buffer_write} is invoked when the serial device is to be written to.
This entry point corresponds to the device driver write entry point.
The @code{frame_buffer_write()} is invoked from a @code{write()}
operation on the frame buffer device.
The frame buffer write function is similar to the read function, and
should handle similar cases involving partial writes.
This method returns RTEMS_SUCCESSFUL when the device is successfully
written to:
@example
@group
@@ -143,19 +206,46 @@ rtems_device_driver frame_buffer_write(
void *arg
)
@{
/*TBD*/
return RTEMS_SUCCESSFUL;
/*printk( "FBVGA write called.\n" );*/
rtems_libio_rw_args_t *rw_args = (rtems_libio_rw_args_t *)arg;
if ( (rw_args->offset >= fb_fix.smem_len) || (rw_args->count < 0) )@{
return RTEMS_UNSATISFIED;
@}
else
@{
/*partial writing*/
if ( (rw_args->offset + rw_args->count) > fb_fix.smem_len )@{
rw_args->count = fb_fix.smem_len - rw_args->offset;
memcpy( (void *) (rw_args->offset + fb_fix.smem_start), rw_args->buffer, rw_args->count);
rw_args->bytes_moved = rw_args->count;
return RTEMS_SUCCESSFUL;
@}
/* best writing case*/
else@{
memcpy( (void *) (rw_args->offset + fb_fix.smem_start), rw_args->buffer, rw_args->count);
rw_args->bytes_moved = rw_args->count;
return RTEMS_SUCCESSFUL;
@}
@}
@}
@end group
@end example
@section Frame Buffer IO Control
@subsection Frame Buffer IO Control
The frame buffer driver allows several ioctls partial compatible with the linux ones
The frame buffer driver allows several ioctls, partially compatible with
the Linux kernel,
to obtain information about the hardware.
Basically `ioctl' commands call `console_control' with the
serial line configuration wich handeles all the services on the interface.
All @code{ioctl()} operations on the frame buffer device invoke
@code{frame_buffer_control()}.
Ioctls supported:
@itemize @bullet
@item ioctls to get the frame buffer screen info (fixed and variable).
@item ioctl to set and get palette.
@end itemize
@example
@group
@@ -171,19 +261,20 @@ rtems_device_driver frame_buffer_control(
switch( args->command ) @{
case FBIOGET_FSCREENINFO:
args->ioctl_return = get_fix_screen_info( args->buffer );
args->ioctl_return = get_fix_screen_info( ( struct fb_fix_screeninfo * ) args->buffer );
break;
case FBIOGET_VSCREENINFO:
args->ioctl_return = get_var_screen_info( args->buffer );
args->ioctl_return = get_var_screen_info( ( struct fb_var_screeninfo * ) args->buffer );
break;
case FBIOPUT_VSCREENINFO:
/* not implemented yet*/
break;
args->ioctl_return = -1;
return RTEMS_UNSATISFIED;
case FBIOGETCMAP:
args->ioctl_return = get_palette( args->buffer );
args->ioctl_return = get_palette( ( struct fb_cmap * ) args->buffer );
break;
case FBIOPUTCMAP:
args->ioctl_return = set_palette( args->buffer );
args->ioctl_return = set_palette( ( struct fb_cmap * ) args->buffer );
break;
default:
@@ -195,5 +286,5 @@ rtems_device_driver frame_buffer_control(
@end group
@end example
Look into @code{rtems/fb.h} for more information on what ioctls exist and on
which data structures they work.
See @code{rtems/fb.h} for more information on the list of ioctls and
data structures they work with.