Presumably the graphics controller fills up a frame buffer for display,
so, if one is not at a certain point using the controller to draw
something, could one write to the frame buffer directly?
Also, AIUI, the RPi communicates with the GPU via memory-based
message buffers, so the GPU must be running some form of background
kernel?
I assume that this must be the purpose of only one of the GPU
processors as running full motion video, say, in an MPEG stream,
must take quite a lot of computer time?
One part of the GPU must be simply concerned with taking the frame
buffer and emitting it as a composite video stream, so I wonder how
the aspect ratio is set up?
Sorry, a bit unstructured in the above, just musing; it's something
that I pick up after a few months before dropping it again; I'm
struggling  to get to grips with the whole GPU thing.
Presumably the graphics controller fills up a frame buffer for display,
so, if one is not at a certain point using the controller to draw
something, could one write to the frame buffer directly?
Also, AIUI, the RPi communicates with the GPU via memory-based
message buffers, so the GPU must be running some form of background
kernel?
I assume that this must be the purpose of only one of the GPU
processors as running full motion video, say, in an MPEG stream,
must take quite a lot of computer time?
One part of the GPU must be simply concerned with taking the frame
buffer and emitting it as a composite video stream, so I wonder how
the aspect ratio is set up?
Sorry, a bit unstructured in the above, just musing; it's something
that I pick up after a few months before dropping it again; I'm
struggling to get to grips with the whole GPU thing.
Presumably the graphics controller fills up a frame buffer for display, so, if one is not at a certain point using the controller to draw something, could one write to the frame buffer directly?
Also, AIUI, the RPi communicates with the GPU via memory-based
message buffers, so the GPU must be running some form of background kernel?
I assume that this must be the purpose of only one of the GPU
processors as running full motion video, say, in an MPEG stream,
must take quite a lot of computer time?
One part of the GPU must be simply concerned with taking the frame
buffer and emitting it as a composite video stream, so I wonder how
the aspect ratio is set up?
Sorry, a bit unstructured in the above, just musing; it's something
that I pick up after a few months before dropping it again; I'm
struggling to get to grips with the whole GPU thing.
Gareth's was W7 now W10 Downstairs Computer wrote:
Presumably the graphics controller fills up a frame buffer for display,
so, if one is not at a certain point using the controller to draw
something, could one write to the frame buffer directly?
According to various official blogs, etc, yes. AIUI, the standard linux framebuffer api works properly on the Rpi.
Also, AIUI, the RPi communicates with the GPU via memory-based
message buffers, so the GPU must be running some form of background
kernel?
Apparently, the GPU runs it's own microcode, which implements the
"VideoCore" architecture. You can find detailed documentation on this architecture, and Broadcom's implementations for the RPi SoCs by searching the fine web.
I assume that this must be the purpose of only one of the GPU
processors as running full motion video, say, in an MPEG stream,
must take quite a lot of computer time?
Of course.
One part of the GPU must be simply concerned with taking the frame
buffer and emitting it as a composite video stream, so I wonder how
the aspect ratio is set up?
I'm not familiar with the internals of the VideoCore GPU, so I can't answer this question. Perhaps a thorough read-through of the VideoCore 3D Architecture Reference Guide would answer this question for you. See
https://docs.broadcom.com/docs/12358545
for details.
Sorry, a bit unstructured in the above, just musing; it's something
that I pick up after a few months before dropping it again; I'm
struggling to get to grips with the whole GPU thing.
HTH
Gareth's was W7 now W10 Downstairs Computer wrote:
One part of the GPU must be simply concerned with taking the frame
buffer and emitting it as a composite video stream, so I wonder how
the aspect ratio is set up?
I'm not familiar with the internals of the VideoCore GPU, so I can't answer this question.
Lew Pitcher <lew.pitcher@digitalfreehold.ca> wrote:
Gareth's was W7 now W10 Downstairs Computer wrote:
One part of the GPU must be simply concerned with taking the frame
buffer and emitting it as a composite video stream, so I wonder how
the aspect ratio is set up?
I'm not familiar with the internals of the VideoCore GPU, so I can't answer >> this question.
Display sizes are communicated to the GPU via the mailbox property
interface, or the mailbox framebuffer interface:
https://github.com/raspberrypi/firmware/wiki/Mailbox-framebuffer-interface https://github.com/raspberrypi/firmware/wiki/Mailbox-property-interface
I'm not sure if the GPU-side registers for changing output video timing (rather than just resolution) are exposed to the ARM.
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