Technical information

7-51
Register Descriptions
13 r/w 0
RxVariableSizeQueues:
Indicates the Rx descriptor mode:
‘
0
’ - Fixed size queue is used.
‘
1
’ - Variable size queue is used.
If the descriptor queue is variable size, it still has a maximum of 256
or 2048 entries depending on
R
X
D
ESC
Q
UEUE
S
IZE
. The host can set
an
END
bit in the last descriptor of the queue, causing the AIC-6915
to automatically wrap to the start of the queue when fetching the
next entry. The AIC-6915 still wraps after 256 or 2048 entries even if
the
END
bit is not set.
This control bit is used for both descriptor queues.
12 r/w 0
Rx64bitBufferAddresses:
Indicates the Rx descriptor type:
‘
0
’ - 32-bit buffer addressing - 4-byte descriptor.
‘
1
’ - 64-bit buffer addressing - 8-byte descriptor.
This Control bit is used for both descriptor queues.
11 r/w 0
Rx64bitDescQueueAddress:
Setting this bit indicates that the
Receive Descriptor Queue is located in 64-bit address space. If this
bit is set, the AIC-6915 PCI Master must use 64-bit addressing mode
to access the queue.
This control bit is used for both descriptor queues.
10:8 r/w 0
RxDescSpacing[2:0]:
Specifies the minimum offset between
descriptors. If the size of the descriptor is larger than the
DescriptorSpacing, the spacing between descriptors is the size of the
descriptor. The first descriptor always starts at the very beginning of
the descriptor list. The spacing is used to calculate the location of
subsequent descriptors.
‘
000
’ - 4-bytes (no space between descriptors)
‘
001
’ - 8-bytes
‘
010
’ - 16-bytes
‘
011
’ - 32-bytes
‘
100
’ - 64-bytes
‘
101
’ - 128-bytes
All other combinations are reserved.
These control bits are used for both descriptor queues.
7r/w0
RxQ1ConsumerWe:
When this bit is set, the software driver is able
to write and update the buffer descriptor queue 1 consumer index.
When the bit is cleared, the Consumer Index is write-protected. The
Consumer Index is implemented in the
R
X
D
ESC
Q
UEUE
1P
TRS
register.
6:0 r/w 0
RxQ1MinDescriptorsThreshold[6:0]:
If the number of receive
buffers available (producer - consumer) is less than
RxQ1MinDescriptorsThreshold
, the AIC-6915 generates a
RxQ1LowDescriptors
interrupt. This function is active only when a
fixed queue size is used.
Table 7-63. RxDescQueue1Ctrl Register (Continued)
Bit(s) rw
Reset
Value Description/Function