AMD Geode LX 600@0.7W Data Book page 320

33234H
Bit Name
3 HPEN_2LB_INV
2 HPEN_3LB_INV
1 HPEN_LB_FILL
0 LPEN_VSYNC
320
DC_ARB_CFG Bit Descriptions (Continued)
Description
High Priority Enable when Any Two Line Buffers Invalid. This bit enables the DC to
arbitrate at high priority if the scaler filter is enabled and any two of the three line buffers
that feed this filter are invalid. (The state of this bit is ignored if the scaler filter is dis-
abled.)
High Priority Enable when Any Three Line Buffers Invalid. This bit enables the DC to
arbitrate at high priority if the scaler filter is enabled and all of the three line buffers that
feed this filter are invalid. (The state of this bit is ignored if the scaler filter is disabled.)
High Priority Enable when Line Buffer Fill in Progress. This bit enables the DC to
maintain high priority requests whenever it is in the process of filling a line buffer. The line
buffer fill requires an entire scan line of data to be read from the data FIFO without inter-
ruption. Because the FIFO typically does not contain a full scan line of data, it is neces-
sary to fetch additional data from memory during this process.
Low Priority Enable at VSYNC. When this bit is set, the DC is forced to arbitrate at low
priority for a number of lines after the start of VSYNC. (This number of lines is pro-
grammed in bits [15:9] (LPEN_END_COUNT)) Because the line buffers, flicker filter buff-
ers, sync buffer, and data FIFO are all cleared at VSYNC, this mechanism prevents the
DC from spending an inordinate amount of time in high priority while filling all of these
buffers.
In most cases this value should be set three or four lines less than the distance between
VSYNC start and V_TOTAL This value may need to be lowered if VBI data is enabled.
During this low priority period after VSYNC, this mechanism overrides the watermark
mechanism for the data FIFO and all of the other mechanisms in this register except the
high priority enable when line buffer fill in progress mechanism enabled in bit 1
(HPEN_LB_FILL). Outside of this period, this mechanism has no effect on the priority
level of outgoing DC requests on the GLIU.
Display Controller Register Descriptions
AMD Geode™ LX Processors Data Book