L64105 LSI Logic Corporation, L64105 Datasheet - Page 35

• Manufacturer Part Number: L64105
• Description: Mpeg-2 Audio/video Decoder
• Manufacturer: LSI Logic Corporation

2.3 Channel Interface
DREQn
PREQn
AREQn
VREQn
Channel Interface
unmasked interrupt condition has occurred in the chip.
The host must read registers 0 through 4 to determine
the cause of the interrupt, take the appropriate action,
and set the Clear Interrupt Pin bit in Register 6
(page 4-10) to deassert INTRn.
DMA Transfer Request
The L64105 asserts this signal when it is ready to receive
a new byte of data from or transmit a new byte of data to
an external DMA controller. The state of DREQn reflects
the condition of internal read and write FIFOs. For DMA
write cycles, DREQn is deasserted when the write FIFO
is not near full (more than one space left) and deasserted
when the FIFO is near full (one space left). For read
cycles, DREQn is asserted when the read FIFO is not
near empty (more than one space filled) and deasserted
when the FIFO is near empty (one space filled). The
maximum transfer rate over this interface is 20 Mbps in
worst case conditions. The peak data rate may increase
above this depending on system SDRAM usage.
PCM FIFO Request
The L64105 asserts this signal when it is ready to receive
a new byte of data in the PCM FIFO, i.e., when the FIFO
is not near full (less than 25 bytes unread). The PCM
FIFO allows the host to send Linear PCM audio samples
to the Audio Decoder in the L64105. PREQn can be used
as a request signal to an external DMA controller.
Audio Transfer Request
The L64105 asserts AREQn when it is ready to receive
a new byte of coded audio data in A/V PES stream mode
(from a transport stream demultiplexer) or a new byte of
any data in program stream modes. The decoder is ready
when the channel input FIFO is not near full.
Video Transfer Request
The L64105 asserts VREQn when it is ready to receive
a new byte of coded audio data in A/V PES stream mode
(from a transport stream demultiplexer). The decoder is
ready when the channel input FIFO is not near full.
VREQn is not used in program stream modes.
Output
Output
Output
Output
2-5