saa8115hl NXP Semiconductors, saa8115hl Datasheet - Page 11

• Manufacturer Part Number: saa8115hl
• Description: Saa8115hl-04 Digital Camera Usb Interface
• Manufacturer: NXP Semiconductors

Philips Semiconductors
9397 750 07395
Product specification
8.5 Transfer buffer
8.6 USB video FIFO
The transfer buffer module (see
to the FIFO of the USB. Moreover the transfer buffer can insert inband
synchronization words in the video data stream. This function can be switched on and
off with INBAND_CONTROL in register VP_TR_CONTROL (0x36).
The synchronization words can only be used with non-compressed data stream and
are formatted like 0x00 0xFF 0x<framecounter>
the number of bits and the frame counter is circular incrementing).
The non-compressed data is formatted like:
where C denotes U-data in the even lines (0, 2, 4 etc.) and V-data in the odd lines
(1, 3, 5 etc.).
The USB video FIFO is programmed via the I
designed to achieve three different packets containing video on the isochronous USB
channel. Video data is contained in a chain of equally sized USB packets, except for
the last packet of a video frame which is always smaller. The video frames can be
separated from each other by one or more 0-length packets. For low frame rates
(below 10 frames per second) there are always 0-length packets in the stream.
The host can synchronize on the smaller packets for the high frame rates and on the
0-length packets for the low frame rates.
For every mode the FIFO must be adjusted. There are three parameters to program
the video FIFO:
Moreover the FIFO is enabled and disabled with FIFO_ACTIVE (0x05).
The write process to the FIFO is controlled by the transfer buffer and not
programmable.
The read process is executed in the PSIE-MMU and is driven by the USB frame
interval (1 ms). Every frame interval the PSIE-MMU tries to read PACKET_SIZE
bytes from the FIFO. This read process will not be started when a new video frame is
stored in the FIFO and there are less than FIFO_OFFSET bytes written. The read
process stops if the next bytes are of another video frame, or if the read-pointer would
overtake the write-pointer.
•
•
•
4 : 2 : 0: <optional sync word><Y0><Y1><Y2><Y3>
<C0><C2><Y4><Y5><Y6><Y7><C4><C6>....,
4 : 2 : 2: <optional sync word><Y0><Y1><Y2><Y3> <U0><V0><U2><V2><Y4>....,
PACKET_SIZE (0x06): this value indicates the length of all packets with video data
except for the last packet of a video frame
FIFO_OFFSET (0x04): this value indicates the number of data in the FIFO before
a new packet will be transmitted over USB
READ_SPACING (0x07): this value indicates the number of 12 MHz clock cycles
between read actions from the FIFO.
Rev. 04 — 10 August 2000
Figure
4) takes care of a smooth transfer of the data
2
C-bus (see
7
<linecounter>
Digital camera USB interface
Figure
SAA8115HL
© Philips Electronics N.V. 2000. All rights reserved.
9
. (Subscript denotes
5). The FIFO is
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