Host Data Structures; Producer And Consumer Indices; Receive Dma Descriptor Queues; The Aic-6915 Receive Data Structures - Adaptec AIC-6915 Programmer's Manual

AIC-6915 Ethernet LAN Controller Programmer's Manual
VLAN support:
– Address filtering based on VLAN
– Ability to delete VLAN tag and number from frame returned to the host
Optional second buffer list for allocating two different buffer sizes

Host Data Structures

Figure 2-1 illustrates the AIC-6915 receive data structures.
Receive Buffers

Producer and Consumer Indices

The transmit, receive, and completion descriptors are stored in circular queues. With the
descriptor queue, the host writes entries into the queue. The AIC-6915 reads from the
descriptor queue and writes to the completion queue, which is in turn read by the host.
The AIC-6915 maintains onchip Producer and Consumer indexes to each queue. The first
element of any queue has an index of 0.
The Producer Index indicates the next entry of the queue to be written, while the
Consumer Index indicates the next entry in the queue to be read.
If Producer and Consumer indices are equal, the queue is empty. If (Producer+1) mod
QueueSize is equal to Consumer then the queue is full. The maximum number of entries
placed in a queue at one time is the queue size minus one.

Receive DMA Descriptor Queues

The AIC-6915 contains two Producer/Consumer type DMA Receive Descriptor Queues
that contain a maximum of either 256 or 2048 entries. A variable option permits the use of
a smaller queue. Host Buffer addresses must be aligned to a word (4-byte) boundary. For
best performance, addresses should also be aligned to cacheline boundary.
2-2
Receive Buffer Descriptor Queue (256/2KByte
Adrs
Adrs
Adrs
Adrs
Adrs
Host Memory
On-chip
Adrs
ListLen
Write Read
BufferLength
(2 Queues are available for 2 different sizes of buffers)
(2 completion Queues allow for 2 priorities)
Figure 2-1. The AIC-6915 Receive Data Structures
)
Receive Completion Queue (2KByte entries)
Start End Len Stat
1 per Frame
Adrs
Write Read