Difference between revisions of "Anatomy of V4L-DVB devices"

From LinuxTVWiki
Jump to: navigation, search
m (fixed links)
m (fixed links)
Line 11: Line 11:
 
== PCI Cards with onboard MPEG-2 Decoder ==
 
== PCI Cards with onboard MPEG-2 Decoder ==
  
Here the [[DVB Frontend]] is connected to the [[AV711x]] hardware [[MPEG-2 Decoder]]. This decoder
+
Here the [[DVB Frontend]] is connected to the [[TI AV711x|AV711x]] hardware [[MPEG-2 Decoder]]. This decoder
 
shares a dualported RAM with the PCI bridge where the MPEG-2 Decoder has its
 
shares a dualported RAM with the PCI bridge where the MPEG-2 Decoder has its
 
[[Wikipedia:Framebuffer:Framebuffer|Video Framebuffer]]. '''(1)'''
 
[[Wikipedia:Framebuffer:Framebuffer|Video Framebuffer]]. '''(1)'''
Line 24: Line 24:
  
 
'''(1)''' With more detail:<br>
 
'''(1)''' With more detail:<br>
The AV711x have his own framebufers on the onboard '''SDRAM''', for MPEG '''I''' and '''P'''
+
The [[TI AV711x|AV711x]] have his own framebufers on the onboard '''SDRAM''', for MPEG '''I''' and '''P'''
 
frames, whose contents are sent to the OSD unit for overlay windows; the OSD unit output is then
 
frames, whose contents are sent to the OSD unit for overlay windows; the OSD unit output is then
 
encoded on PAL or NTSC display formats and output in CVBS (Composite+Video+Blanking+Synchronism)
 
encoded on PAL or NTSC display formats and output in CVBS (Composite+Video+Blanking+Synchronism)
Line 31: Line 31:
 
colour space conversion, etc), is sent by PCI Bus Mastering to the Video Framebuffer, normaly on
 
colour space conversion, etc), is sent by PCI Bus Mastering to the Video Framebuffer, normaly on
 
a VGA card or in main memory for a V4L application. The dualported RAM ('''DPRAM'''), which is
 
a VGA card or in main memory for a V4L application. The dualported RAM ('''DPRAM'''), which is
connected to the AV711x and to the PCI bridge, is used for all the communications between the
+
connected to the [[TI AV711x|AV711x]] and to the PCI bridge, is used for all the communications between the
DVB drivers and the AV711x: To send the firmware and commands, to send MPEG-2 DVR streams (to be  
+
DVB drivers and the [[TI AV711x|AV711x]]: To send the firmware and commands, to send MPEG-2 DVR streams (to be  
 
decoded and show as video/audio), to receive MPEG-2 TS packets, PES data or sections  
 
decoded and show as video/audio), to receive MPEG-2 TS packets, PES data or sections  
 
(demultiplexed from the stream), etc.
 
(demultiplexed from the stream), etc.

Revision as of 23:57, 6 January 2008

Introduction

Digital Video Broadcast Receivers exist in many different flavours. In order to give you an idea of what we all support with the linux-dvb drivers and why some things look quite complicated this page lists the common types:

Minimal Configuration

A minimal device for DVB reception at the PC consists of a DVB Frontend and some FIFO Memory. This FIFO samples the MPEG-2 Transport Stream delivered by the frontend and makes it accessible (e.g. by a port-interface, memory-mapped or a bus-interface like USB or IEEE1394) to the host processor.

All modern peripheral DVB devices follow this approach: common PCI cards, nearly all USB adapters and IEEE1394 DVB devices. Only they are supported directly by Microsoft's BDA architecture.

PCI Cards with onboard MPEG-2 Decoder

Here the DVB Frontend is connected to the AV711x hardware MPEG-2 Decoder. This decoder shares a dualported RAM with the PCI bridge where the MPEG-2 Decoder has its Video Framebuffer. (1)

Examples:

The Onboard Decoder makes these cards somewhat expensive.


(1) With more detail:
The AV711x have his own framebufers on the onboard SDRAM, for MPEG I and P frames, whose contents are sent to the OSD unit for overlay windows; the OSD unit output is then encoded on PAL or NTSC display formats and output in CVBS (Composite+Video+Blanking+Synchronism) or Y/C (Luminance+Chrominance) or RGB (Red+Green+Blue) modes; the OSD unit output is also sent in digital format to the PCI bridge, which after optional transformations (scaling, cliping, colour space conversion, etc), is sent by PCI Bus Mastering to the Video Framebuffer, normaly on a VGA card or in main memory for a V4L application. The dualported RAM (DPRAM), which is connected to the AV711x and to the PCI bridge, is used for all the communications between the DVB drivers and the AV711x: To send the firmware and commands, to send MPEG-2 DVR streams (to be decoded and show as video/audio), to receive MPEG-2 TS packets, PES data or sections (demultiplexed from the stream), etc.

Standalone STB

In a SetTopBox the Frontend directly feeds the built-in hostprocessor (usually with onchip MPEG Decoder). These processors are mostly based on embedded ARM-, MIPS-, PowerPC-Cores with additional peripheral units like i2c-, IDE-, network-, Smartcardcontrollers, Demultiplexers, Decoders, Audio- and Videointerface.

Modern STB processor chipsets move more and more decoder tasks into Firmware or software, this allows implementation of new codecs like DivX, MPEG-4, WMV and even late updates of products in the field. We expect that this evolution continues.

STBs with interface to the PC

Have an integrated embedded processor with MPEG-2 Decoder and are able to work standalone. You can connect your PC, e.g. using the USB or Firewire port to record and play back DVB transmissions on your TV.