Curtiss-Wright SCRAMNet+ SC150e, Hardware Reference Manual

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SCRAMNET OVERVIEW
Copyright 2007 2-10 S SC150e HARDWARE REFERENCE
2.9.2 High Performance (HIPRO) Mode
HIPRO provides an efficient means to transmit 8-bit and 16-bit data transactions as one
32-bit network write. It also provides a means of keeping 32-bit data from becoming
fractured.
EXAMPLE #1:
A floating-point length numeric sent in 8-bit or 16-bit pieces may not be accurately re-
assembled at the destination.
EXAMPLE #2:
The receiving node may otherwise try to use part or half of such a value before the entire
32 bits is received.
HIPRO WRITE
The S SC150e network message is based on 32-bit longword data. This
means if any 8-bit field of the 32-bit buffer is changed, the entire 32-bit message is
transmitted. If a host is limited to only 8-bit or 16-bit data bus transactions the network
throughput is quartered or halved, respectively.
HIPRO mode permits a 32-bit location to be set up in shared memory so any initial write
smaller than 32 bits to that location will not automatically go onto the network. The 32-
bit write to the network will only occur when all four bytes within the 32-bit location
have been written through subsequent writes by the host CPU. This can be accomplished
by four consecutive 8-bit or two consecutive 16-bit writes to the SCRAMNet memory.
NOTE
: HIPRO WRITE will not work if Disable Host to Memory Write CSR2[8] is
set, or when writing two separate shortwords while using interrupts.
2.9.3 Holdoff Mode
It is possible that the Transmit FIFO can become full when the host is writing to the
S SC150e interface faster than the network can absorb the data.
In Holdoff
mode, the host write cycle is automatically extended until the S
SC150e Transmit FIFO buffer transmits at least one message. This prevents the loss of
data and is transparent to the user.
In some system designs, and on some computer buses, it is not desirable or effective to
have the write cycle lengthened to match network throughput—even at the expense of
possible data loss across the network. In this case you can disable this option by setting
CSR8[1] ON. Transmit FIFO 7/8 Full CSR1[2] can then be used to control the data flow
via software control.
2.9.4 Loopback Modes
Loopback mode is used for testing and routing data normally transmitted onto the
network back into the node. This mode is used to check performance internally (Wire
Loopback) at the Media Card (Mechanical Switch Loopback) and Transmit/ Receive
(Fiber-optic Loopback).