HP Visualize J200 Reference Manual page 62

EISA interface
Industry Standard Connectivity I/O (EISA)
J Class relies on EISA to serve many I/O expansion needs. Examples of functionality available on EISA
include 802.3, 802.5, FDDI, SCSI, VME adapters, X.25, Serial MUX, etc.. While the EISA specification
allows for higher throughputs (33 MB/second for DMA Masters), J Class's implementation supports the
more modest throughputs estimated below:
EISA DMA MASTER:
– 17 MB/sec for 32byte Master READ from memory
– 25 MB/second for 32 byte Master WRITE to memory
HOST CPU DIRECT I/O:
– 5 MB/second for 4 byte DIO READ from EISA Device
– 12 MB/second for 4 byte DIO WRITE to EISA Device
The EISA interface ASIC (WAX) is connected to the GSC bus also serving the GSC Expansion
connectors in the I/O expansion card cage. In essence, EISA devices and GSC devices on the same GSC
bus must share the bandwidth of the interconnect. Because it is not possible to decouple the bandwidth of
the EISA and GSC devices at this time, it may be important to have the appropriate expectations
regarding the distribution of GSC bandwidth if one considers using EISA for higher bandwidth
applications.
Figure 4–3. GSC Bandwidth as a Function of EISA bandwidth (Memory READ).
Figure 4–3 shows a simple distribution of GSC bandwidth based on a shared bandwidth condition
involving a native GSC device and an EISA resident device. In essence, as the amount of EISA bandwidth
increases, the amount of available GSC bandwidth decreases. For instance, a 10 Mbyte/s FDDI controller
would consume about 60% of the total GSC bus bandwidth, leaving only 40 MB/s for a native GSC
device. In general, because the EISA and GSC bandwidths are coupled, the time spent on EISA is
equivalent to the time spent on GSC, but at only one fourth the throughput.