Adaptec 1737100 Programmer Manual - Page 110

AIC-6915 Ethernet LAN Controller Programmer's Manual Table 7-46. TxDescQueueCtrl Register (Continued) Reset Bit(s) rw Value Description/Function 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. 3 r/w 0 DisableTxDmaCompletion: If this bit is set, the AIC-6915 does not transfer completion descriptors and does not set the interrupt status bit TXDMADONEINT. 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. 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 "END" bit in the appropriate descriptor field. 7-38