![Systran SCRAMNet+ VME3U Hardware Reference Manual Download Page 114](http://html1.mh-extra.com/html/systran/scramnet-vme3u/scramnet-vme3u_hardware-reference-manual_1423581114.webp)
HOST ACCESS TIMING
Copyright 1995, S
YS
I
RAN
Corp.
D-10
VME3U H/W REFERENCE
FIRST CYCLE
1.
AS, DSx fall - Start of Cycle (106 ns delay to decode address).
2.
HREQ asserted - WRITE request to DPRC
-
DPRC asserts HREQ_PEND Request accepted
-
DPRC buffers data
-
DPRC asserts HACK.
3.
Host linterface logic generates DTACK 53 ns later.
4.
AS and DSx are de-asserted.
5.
Minimum time AS is inactive is 30 ns.
SECOND CYCLE
The second cycle shows a second host WRITE is initiated 30 ns later according to
minimum VME requirements. Under normal operating conditions it is unlikely the host
will be able to turn around that quickly. An HREQ cannot be generated since the first one
is still being serviced. Additionally, in this “worst case” scenerio, three network
transactions must be processed before the previous host request is cleared.
Once the network transactions are cleared, the buffered data from the host WRITE can
be written to shared memory which clears the WRITE buffer. This takes 240 ns from the
request to the acknowledgement.
DPRC has not yet written to shared memory
6.
AS, DSx fall - Start of second host cycle.
7.
HREQ cannot be asserted since the previous request is still pending.
-
DPRC receives 3 network WRITEs
-
DPRC processes network WRITEs
-
DPRC performs host WRITE to shared memory
8.
HREQ_PEND de-asserted (No longer busy)
-
DPRC asserts HREQ_PEND - WRITE request accepted
-
DPRC buffers data
-
DPRC asserts HACK
-
Host Interface logic generates DTACK
9.
AS and DSx are de-asserted
Summary of Contents for SCRAMNet+ VME3U
Page 1: ...SCRAMNet Network VME3U Hardware Reference Document No D T MR VME3U A 0 A2...
Page 2: ......
Page 4: ......
Page 52: ...OPERATION Copyright 1995 SYSIRAN Corp 4 26 VME3U H W REFERENCE Figure 4 10 Quad Switch...
Page 78: ......
Page 92: ......
Page 96: ......
Page 104: ......
Page 115: ...E APPENDIX E CONFIGURATION AIDS TABLE OF CONTENTS...
Page 116: ......
Page 121: ...F APPENDIX F ACRONYMS...
Page 122: ......
Page 124: ...ACRONYM Copyright 1995 SYSlRAN Corp F 2 VME3U H W REFERENCE This page intentionally left blank...
Page 125: ...G APPENDIX G GLOSSARY...
Page 126: ......