ADSP-214xx SHARC Processor Hardware Reference 8-9
Media Local Bus
the local channel buffer memory is 124 quadlets. At reset each channel has
four quadlets each.
The buffer depth, buffer threshold and buffer start address for each chan-
nel is programmed using the respective MLB_LCBCRx register. The buffer
threshold is used by hardware channels in I/O mode only.
Hardware uses the local channel buffer threshold to determine when to
issue an I/O service request to system software. I/O service requests are
generated when:
• The number of valid qualdets in the local channel buffer falls
below the threshold for transmit channels or:
valid quadlets <=
MLB_LCBCRx (programmed using TH bits)
Figure 8-2. Local Channel Buffer Threshold Mechanism
TX DATA
INPUT
TX DATA
OUTPUT
TRANSMIT SERVICE REQUEST GENERATED
(NUMBER OF VALID DATA QUADLETS <= BUFFER THRESHOLD)
RX DATA
OUTPUT
RX DATA
INPUT
RECEIVE SERVICE REQUEST GENERATED
(NUMBER OF FREE DATA QUADLETS <= BUFFER THRESHOLD)
FREE QUADLETS
VALID DATA
VALID DATA
FREE QUADLETS
BUFFER DEPTH
BUFFER THRESHOLD
BUFFER DEPTH
BUFFER THRESHOLD
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