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IDE to SCSI Adapter - discrete logic - reverse engineering candidate?

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I think most of the people who spend $100+ for a Jackhammer or ATTO SEIV are not doing video capture, they just like the speed increase and are hardware lovers in general. Still a SATA Nubus card would require some very specific skills in hardware interfacing and code writing few people still have. 

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1 hour ago, Gorgonops said:

I'm fairly certain the Beige only has the *slow* bus. Unlike some of the bigger Beige PPC iron the internal and external connector are on the same chain (like a Quadra or older class machine), and that means the MESH integrated to the Heathrow ASIC is limited to 5MB/s.

 

The way I remember it (need to check the developer notes) the Beige G3 actually uses a 53C96 or 53C94 cell for its SCSI support, but (and I may be confusing this with the B&W) there's a MESH cell in one of the big I/O chips that doesn't have its signal brought out to pins.   It's just there because some part of the OS expects to find it.

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The Beige G3 was sold with a third party 68 pin SCSI card if you needed it to run as a server with SCSI HDs. Internal SCSI was fine for scanners which is what was probably popular at the time along with external SCSI removable media that would not need a faster interface (at that time).

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1 hour ago, Unknown_K said:

Still a SATA Nubus card would require some very specific skills in hardware interfacing and code writing few people still have. 

 

Yeah, I don't think anyone's advocating to build a NuBus SATA card. It would be neat to have, of course, but there's already solutions for those Macs.

 

The point being made is that no NuBus machines need that particular kind of performance boost.

 

Even the PowerPC Macs in general arguably don't need it and even G3s/G4s running Mac OS 9 arguably can't take advantage of the performance reasonably well, but it's at least an option there, versus trying to build something to max out the second SCSI bus on the higher end 7000/8000/9000 powermac boards.

 

An affordable SCSI-to-SATA adapter would be very neat, I think a lot of people would like it, but I don't think it's necessary.

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1 hour ago, trag said:

 

The way I remember it (need to check the developer notes) the Beige G3 actually uses a 53C96 or 53C94 cell for its SCSI support, but (and I may be confusing this with the B&W) there's a MESH cell in one of the big I/O chips that doesn't have its signal brought out to pins.   It's just there because some part of the OS expects to find it.

According to the dev note both internal and external SCSI are hanging off the Heathrow, there is no separate SCSI chip. (And if you look at the specs for Heathrow in the PDF you'll see that the built-in SCSI is based on MESH; MESH *is* 10MB/s capable in the stand-alone ASIC used in various "thousand-series" machines but it doesn't appear to be so in Heathrow.) External SCSI on the machines that had both was buried in the "Curio" ASIC. Considering what Heathrow has it in it I can't help but wonder if it's actually more of a "Curio" descendant than MESH. (Or maybe the SCSI in Curio is just a brain-dead version of MESH too?)

 

And yes, the "Paddington" ASIC that was used in the tray-loading iMacs and B&W G3 does apparently have the MESH cell from Heathrow still buried in it but not connected to anything. I've heard vague rumors that the Paddington ASIC actually ended up in some Beige G3s, either in prototypes or possibly even shipped, but I don't know what to make of that. I suspect it's confusion based on some Beige G3 models shipping with 10/100 ethernet *cards* installed. (Main difference between Heathrow and Paddington is the latter has 10/100 ethernet integrated instead of just 10m.)

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1 hour ago, Gorgonops said:

 (And if you look at the specs for Heathrow in the PDF you'll see that the built-in SCSI is based on MESH; MESH *is* 10MB/s capable in the stand-alone ASIC used in various "thousand-series" machines but it doesn't appear to be so in Heathrow.) External SCSI on the machines that had both was buried in the "Curio" ASIC. Considering what Heathrow has it in it I can't help but wonder if it's actually more of a "Curio" descendant than MESH. (Or maybe the SCSI in Curio is just a brain-dead version of MESH too?)

 

Thank you for the links.    You are indeed correct.  The Hardware Developer Note says that Heathrow contains a MESH controller.   Color me surprised.    I thought/expected it was basically CURIO with extra stuff brought inside.   Although, CURIO was an AMD chip, so maybe Apple didn't have access to all the rights/designs, or something and had to make Heathrow from scratch.

 

On the other hand....

 

Wandering into speculation country....

 

The separate Fast SCSI bus first showed up on the NuBus PowerMac 8100 and 9150.    It was based on the 53CF96 which was made by a number of folks.   I'm not sure where the design originated, maybe NCR.    But AMD also sold one and I think Zilog might have as well.   NCR mutated into Symbios (?) and later LSI Logic.

 

The separate Fast SCSI bus on the next generation, the PCI PowerMacs, used the MESH controller, in exactly the same package as the 53CF96.    I strongly suspect that the MESH is just a licensed version of the 53CF96.  Or, perhaps, Apple's home rolled version to avoid licensing fees?  In the volumes they were using, it may have paid to roll their own.   One of these days, I'm going to replace a MESH with a 53CF96 or vice versa and see what happens.

 

Meanwhile, the CURIO chip which first appeared in AV Quadras and was used in both the NuBus and the PCI PowerMacs, contained a 53C94 or 53C96 cell.  In all those machines the CURIO chip provided the slower internal/external SCSI bus, as well as serial ports and ethernet.

 

The 53C94/96 is closely related to the 53CF96.

 

So, I wonder, if Heathrow was an Apple design, and they put a 53C94/96 in Heathrow, would it be inaccurate for them to claim that Heathrow contains a "MESH-based SCSI controller".

 

I am also now curious to see what SCSI Probe says about the Beige's built in SCSI bus...

 

 

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I vaguely recall the Wikipedia page for the 53C9x series claims that MESH is indeed a lightly cooked version of that chip, so, sure, in a roundabout way Apple may well be being both truthful and elusive with the claim that the SCSI built into Heathrow is "MESH Based" even though it's actually a lower-spec core from the same licensed family.

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