Technical information

3-5
Transmit Architecture
Transmit Register Set
The following is a list of transmit parameters programmed by the driver during
initialization.
■
Transmit descriptor queue size and base address.
■
Completion queue size and base address.
■
Descriptor type, minimum spacing, and skip field size.
■
FIFO size (4KBytes).
■
PCI cache line size.
■
DMA burst size.
■
Transmit start threshold.
■
DMA priority threshold.
The following is a list of transmit registers used during a host to AIC-6915
communication.
■
High-priority queue consumer index. (Written by the AIC-6915, read by driver).
■
High-priority queue producer index. (Written by the driver, read by the AIC-6915).
■
Low-priority queue consumer index. (Written by the AIC-6915, read by the driver).
■
Low-priority queue producer index. (Written by the driver, read by the AIC-6915).
■
Completion queue consumer index. (Written by the driver, read by the AIC-6915).
■
Completion queue producer index. (Written by the AIC-6915, read by the driver).
Transmit DMA Buffer Descriptor Queues
There are two Buffer Descriptor Queues for transmission. One for high-priority traffic and
one for low-priority traffic. Each Descriptor Queue size has a maximum size of 16-KBytes.
The actual length is variable with the end-of-queue defined by the “
E
ND
” bit. The
definition of the “
E
ND
” bit is described in the following sections. Both high-priority and
low-priority queues have base addresses aligned on a 256-byte boundary.
Five descriptor types are supported. The driver must program the descriptor type during
initialization. Descriptors are in multiples of 8-bytes. The Descriptor Queue is aligned on a
256-byte boundary. There is a “Skip field” defined in front of each packet to reserve space
for the driver to store information. The “Skip field” size varies from 0 bytes to 128 bytes
and is programmed by the driver during initialization. The AIC-6915 does not read or
write to the “Skip field”.
Type 0, 32-bit Addressing Mode (Frame Descriptor)
Type 0 enables the driver to execute a simple and fast copy of a TCB data structure (given
by the upper layer software as a frame descriptor) to the Descriptor Queue area.