Technical information

7-38
AIC-6915 Ethernet LAN Controller Programmer’s Manual
Note:
Maximum transmit descriptor queue length 16-KBytes for the high-priority
queue and 16-KBytes for the low-priority queue. Priorities cannot be mixed
within the same queue. Overall queue size is programmable by setting the “
E
ND
”
bit in the appropriate descriptor field.
6:4 r/w 0
MinFrameDescSpacing:
Defines the minimum number of bytes
between two consecutive frame/buffer descriptors. This feature is
particularly useful for operating systems that have a variable
number of fragments per frame (Netware).
‘
000
’ - not restricted
‘
001
’ - 32 byte
‘
010
’ - 64 byte
‘
011
’ - 128 byte
‘
100
’ - 256 byte
all other combinations are reserved.
Note
: When the software driver restricts the frame descriptor size, it
must be aware that the maximum number of possible fragments per
frame is limited.
3r/w0
DisableTxDmaCompletion:
If this bit is set, the AIC-6915 does not
transfer completion descriptors and does not set the interrupt status
bit
T
X
D
MA
D
ONE
I
NT
. If the bit is cleared (default state), the
AIC-6915 transfers a completion descriptor after DMA-transferring
the entire frame, then sets the interrupt status bit if the bit ‘
INTR
’ is
set in the first buffer/frame descriptor of the frame.
2:0 r/w 0
TxDescType:
Indicates the transmit descriptor type:
‘
000
’ - Basic frame descriptor, 32-bit addressing.
‘
001
’ - Basic buffer descriptor, 32-bit addressing.
‘
010
’ - Basic buffer descriptor, 64-bit addressing.
‘
011
’ - Special netware frame descriptor with 32-bit addressing.
The AIC-6915 builds the Ethernet media header. This type has 4
subtypes associated with it.
‘
100
’ - Special DOS/OS2 Frame descriptor with 32-bit
addressing. Same as type 0, but the Length field is bytes 4:3
instead of 1:0 in type 0.
All other combinations are reserved.
Table 7-46. TxDescQueueCtrl Register (Continued)
Bit(s) rw
Reset
Value Description/Function