Introduction

The SGI built Digital Audio Option PCI card (aka Radical, marketing code PCI-AUD-8C) is now supported with the introduction of the Origin 200 QC (Quick Cache) server. The Radical will plug into the older Origin 200's PCI slots and work for the most part even though it is not supported. The only requirement is that you load certain patches on top of Irix 6.4. The reason that this combination of Radical and O200 is so late in coming is because the initial design of the PCI motherboard did not include support for what is known as the feature connector. The connector was left out of the original O200 PCI motherboard because it blocked air flow and added extra cost to the system which was not originally targeted for audio serving. The good news is that the new Origin 200 QC (Quick Cache) now fully supports Radical!

Feature Connector

This feature connector is an extra 6 pin edge connector that is situated between the PCI connector and the rear connector metalwork. The connector conveys three synchronizing signals to the card to support realtime features such as UST (unadjusted system time) and Ksync (Kitchen Sync). The UST Clock signal is the most critical of the three. In the O200, it is a 1.25 MHz global clock that feeds the UST counters in the HUB ASICS. In other SGI platforms such as Octane and Origin 2000, this signal is fed to all I/O slots so that digital media hardware will have a common clock to increment their UST counters. Using this clock insures that the counters in the digital media hardware will be consistent with the counters in the HUB ASICS (all of which can be accessed from user software). The Ksync signals provide a clean way of piping Video Sync around inside the system instead of plumbing it externally. Nice, but not as essential as the UST Clock.

Life without the Feature Connector

Radical was designed to function without this feature connection because it was known that the O2 was not going to support this connection either. So, in the case where the Radical finds its signals floating, the hardware substitutes the 33 MHz PCI clock for UST clock. The audio driver senses this on startup and programs the on board dividers appropriately to make the UST count proceed at a rate very close to HUB clock but drifting with respect to it.

It is less critical in the O2 because there is no way of plugging more than one PCI card in to it. But in a two module O200, you can plug in six Radical cards! In order to support audio sample accurate sync between radical cards, the UST counters must be clocked from the same source. So, in a one module O200, there is no problem since all three cards are being clocked from the same PCI clock. In a two module O200, each module has its own PCI clock, so sample accurate sync is dependent on the drift between these two separate clocks and therefore can not be guaranteed.

In summary, if you can meet the criteria below, then you will have no problems with older O200s and older Radical cards:

• You can achieve sample accurate sync if you can
  • operate with 3 or less Radical cards AND
  • you can keep all Radicals in the same module AND
  • you do not need to sync this audio with video or tserialio.

OR

• If you have no need for sample accuracy between audio devices and you do not need to sync this audio with video or tserialio, you will be fine.

If you do use a Radical in these older systems, you will get the following message on the console whenever you start up the system:

               PCI Digital Audio I/O option feature connector not detected!
               Be sure that the feature connector is properly installed.
               Note that IP29 processor modules before 030-1244-001 rev A
               do not support the PCI Digital Audio I/O option.

Do not fear. It will still work, but beware of the caveats mentioned above.

The Fix

Even though most of the applications will work fine because they fit the above successful criteria, the engineers at SGI were not satisfied and proceeded to fix the issues. A new version of the IP29 motherboard was spun (known internally as the "media ready" IP29) along with new versions of the PCI backplane and Radical card to accommodate a connection scheme better suited to the O200's internal construction. A small AMP modu connector was added to both the Radical card and the PCI backplane to receive a short cable between them which connects the UST clock and Ksync signals. The new Radical card still has the old style edge connector as well as the new so it can work in all platforms. The marketing code was thus changed to PCI-AUD-8C-ALL to indicate this.

Although it is unsupported, you can use a kluge cable to connect old -001 Radical cards with the new O200.

Even though this connector has been shipping in O200s for a while now, Radical is not officially supported on O200s earlier than the O200QC (Quick Cache). This is because SGI management wanted to reduce the spares needed in the field.

Below is a matrix showing the various part numbers and the support you can expect for them.

A Fully supported.

B Fully functional but not supported.

C Will work, but UST is clocked from PCI clock and therefore drifts with respect to system UST and Radicals in other modules. And, sorry, no ksync features.

D Will explode in flames! Call 911.

You can use the hinv -m command to see what particular assemblies your system has. The beginning of the rather verbose output looks like this:

    PIMM_2XT5_2M Board: barcode GBX621     part 013-2284-002 rev  A
            IP29 Board: barcode GBX997     part 030-1244-001 rev  H

The first is the Processor module (or PIMM). Any PIMM will work with Radical. The second is the IP29 motherboard. The 1244 is the one that has the digital media support for UST clock and ksync. The 1025 does not. Unfortunately, the PCI backplane does not appear in this list since it does not have a NIC. You have to actually look inside to see what PCI backplane you have. The 1026-002 is easily identified by three 6 pin headers along side the PCI connectors. The 1026-001 does not have these headers.

Gotcha!

On some rare occasions, I have seen 1025 motherboards attached to 1026-002 PCI backplanes! This is very bad since, by looking at the PCI backplane, you think you have a "media ready" O200, so, you connect the cable. The Radical's hardware detects that you have connected the cable and switches away from the PCI clock to the non-existent UST clock and is hence not clocked. If you fall into this unfortunate trap, the Rad driver will complain at startup like this:

PCI Digital Audio I/O option UST not incrementing!
Possible cause: incompatible versions of IP29 and PCI mother boards.

Or just...

RAD UST not incrementing

And, none of the audio applications that use UST will work properly.

Solution: Remove the cable for C support, or get 1244 motherboard for B or A support.