The SMA's online computer network is currently in a transitional period. There was not a great deal of uniformity in the original choices for the computers which were to control the SMA's hardware. Most of the control computers where hosed in a VXI chasis, but the correlator was designed around the VME bus. The antenna computers and "hal" (the central computer) were to be x86 PC-lookalikes, on a VXI bus, running LynxOS. The IF-LO computers were to be 680x0 computers, running VxWorks, on a VXI bus. And the correlator was to be a collection of 680x0 processors, on VME busses, running VxWorks.
In 1997, we decided that for most of our computers, the high-level features of the VXI bus were not being used. Indeed, almost all of the I/O cards we were puting in our VXI crates were in fact VME cards. The few VXI cards we did have were both expensive and sluggish. So we decided to try to adopt a single bus, processor architecture and operating system throught the online system. We decided to standardize with Motorola PowerPC (PPC) CPUs on a VME bus, running LynxOS. We hope that soon all of the online computers, with a single exception, will be of this type. The single exception will be the computer called "blocks", which will control the synthesizers for the correlator's first downconverter. However even the nonstandard "blocks" computer will use LynxOS.
As of now (late 1998), we are still using the x86 VXI computers in the two prototype antennas, and for "hal". The newer (PPC) systems are being used in antenna 1, for servo development, and in the correlator crates. We expect that the antennas will convert to PPC systems in 1999, when the new servo system in retrofitted into the antennas (if not earlier).
A diagram of the proposed online network is shown here . The system has several sorts of computers. On the top level, "sma1" and "smadata" are Sun workstations running Solaris. There is no realtime load on these two computers. sma1 is the computer that was called "gateway" in much of the earlier documentation. The name was changed to avoid confusion with computers made by Gateway Corporation. It is intended that sma1 will be the only computer with which the astronomer/operator will need to directly interact. SMARTS, the SMA's control program, will run on sma1. The other Solaris machine is smadata, which will receive the data produced by the correlator, collect header and status information, and log the data into the Sybase database system.
All of the computers are connected by ethernet. There will be a second 100 Mbps ethernet connecting the correlator crates with smadata. This second ethernet will be used only for pumping correlator data to smadata. The antenna computers ("acc1", "acc2" ... "acc8") will each have a Reflective Memory (RM) card in it, connected to a matching RM card in hal. The CSO and JCMT have agreed to place RM cards in their antenna computers, to support expanded array interferometry. Thus hal will have up to 10 RM cards in it. Nearly all of the computers will be sent IRIG-B time codes from a GPS receiver in hal. This should provide time synchronization good to about 2 microseconds.
The general-purpose realtime computers will all run the LynxOS operating system. The DSPs within on the correlator boards will run a "scheduler" developed at MIT/Haystack. The embedded microcontrollers, performing such operations as tuning the Gunn LO system and operating the secondary phase rotators, will run standalone code with no OS.
