Adaptec 1737100 Programmer Manual - Page 35
Transmit Register Set, Transmit DMA Buffer Descriptor Queues
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Transmit Architecture Transmit Register Set The following is a list of transmit parameters programmed by the driver during initialization. s Transmit descriptor queue size and base address. s Completion queue size and base address. s Descriptor type, minimum spacing, and skip field size. s FIFO size (4KBytes). s PCI cache line size. s DMA burst size. s Transmit start threshold. s DMA priority threshold. The following is a list of transmit registers used during a host to AIC-6915 communication. s High-priority queue consumer index. (Written by the AIC-6915, read by driver). s High-priority queue producer index. (Written by the driver, read by the AIC-6915). s Low-priority queue consumer index. (Written by the AIC-6915, read by the driver). s Low-priority queue producer index. (Written by the driver, read by the AIC-6915). s Completion queue consumer index. (Written by the driver, read by the AIC-6915). s 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 "END" bit. The definition of the "END" 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. 3-5
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