Direct Sony-Style RS-422 Deck Control:
Introduction and Scope

Many developers have asked us how to make an SGI do field-accurate capture from and laydown to a directly connected Sony-Protocol RS-422 VTR. This section provides some hints to help you accomplish this:

• information on getting 422 in and out of your SGI machine.

• complete sample code for doing full-rate, full-size, field-accurate uncompressed 422 deck controlled captures and laydowns with a Sony DVW-A500 deck on an IRIX 6.3 O2 using tserialio.

• hints on how you might do deck control on an SGI system which offers millisecond-granularity IRIX process scheduling guarantees, which today means a multiprocessor system.

Scope

• We have an SGI machine whose video inputs and outputs are hooked to a VTR. The SGI and the VTR are genlocked off of a common house sync.

• The SGI machine is capable of full-rate, full-size uncompressed video disk i/o, and is therefore one of the platforms listed in Uncompressed Video Disk I/O: Introduction and Scope. See below for a JPEG note.

• The SGI's serial port is hooked directly to the deck's RS-422 deck control port (often called "remote in" port). A 232-to-422 converter is required on some platforms (see Getting 422 in and out of Your SGI).

• The deck speaks some close variant of the protocol spoken by the Sony DVW-A500 deck. This includes all of the Sony BVW and DVW decks as well as hundreds of others. This protocol group is known by more names than I can count ("Sony 9-Pin Protocol," "Sony BVW Protocol," "REMOTE-1 Protocol," "P2,"...). We will assume you are familiar with the protocol, how it is very important to send commands and service responses within a certain time after the video vertical sync, and how this is a difficult feat to accomplish on a multitasking operating system like single-processor IRIX.

  You can obtain an aggravatingly poorly translated, overpriced jinglish translation of Sony's "BVW/DVW Protocol Manual 9-977-544-01" by contacting your Sony rep. Or, you can read Rick Davis' excellent "lurker's guide" to the Sony protocol and get almost all the same information.

  Perhaps the hardest thing about implementing direct deck control is the small but critical variations between behavior on different "Sony Protocol" decks. Almost none of these variations are documented: you have to have each deck to detect and work around them. Often a single make and model of deck will exhibit variations based on its firmware rev. We will show you code that works on a Sony DVW-A500, and point out some of the more blatant areas where decks differ (such as edit delay). Supporting lots of different decks is up to you.

• The goal is to capture a specified range of fields from the deck's tape to the computer's disk in one pass, or lay down a specified range of fields from the computer's disk to the deck's tape in one pass. The operation transfers exactly the right fields. Much of what we discuss here is also useful on systems that need to do multi-pass capture or laydown.

• Non-real-time control of external video disk recorders such as those from Abekas or Accom (Uncompressed Video Disk I/O: Introduction and Scope describes these devices).

• V-LAN-/MiniVAS-style deck control, where the RS-422 communication is handled on a piece of dedicated external hardware which triggers the computer via GPI. The computer communicates with the hardware in non-real-time using RS-232.

• Platforms that can do full-rate, full-size JPEG platforms such as cosmo1 on Indy/Indigo2, cosmo2 on Indigo2/Octane, and ICE on O2. As long as the platform has a working UST/MSC implementation, all of what we describe here applies to these platforms as well. But we have chosen to stick with the uncompressed platforms to simplify the presentation.

• Synchronized audio capture and laydown.