nubus scsi card any benefit?

[Phipli]

Technically we could write an extension to poke registers for the MESH and up Beige G3 SCSI speeds to 10MB/s.

Happy to help make it if someone with a better understanding of the 53CF96 registers lets me know what needs poking in what order



Although we should probably start a new thread for that. It might also be useful for machines with a 53CF96 swapped in.

 

[croissantking]

Technically we could write an extension to poke registers for the MESH and up Beige G3 SCSI speeds to 10MB/s.

Happy to help make it if someone with a better understanding of the 53CF96 registers lets me know what needs poking in what order

View attachment 98928

Although we should probably start a new thread for that. It might also be useful for machines with a 53CF96 swapped in.

This would be very cool - a dedicated thread sounds sensible.

Would enabling 10MB/sec mean disconnecting external SCSI devices?

 

[Phipli]

Would enabling 10MB/sec mean disconnecting external SCSI devices?

It would mean using short cables at least

 

[trag]

Datasheets ("Data Manuals"), in case this is helpful.

The 53CF96 is expensive, in my experience. $10 - $20 each.

The 53C96, I have a reel or brick or something around here somewhere, from back when surplus electronics were basically given away on Ebay.

 

[joevt]

Technically we could write an extension to poke registers for the MESH and up Beige G3 SCSI speeds to 10MB/s.

Setting SCSI speed might not be a SCSI controller register setting. It may have something to do with SDTR messages? I haven't looked at the SCSI spec. I don't think MESH or CURIO has SCSI chips used in Power Macs has a register for SCSI speed.

• joevt —
  2026-05-18, 3:03 PM
  Heathrow in Gossamer:
  

  MESH provides transfer rates of up to 10MB/sec however software limits transfer rates to 5MB/sec because external SCSI devices using our current cabling system have a difficult time with the maximum data transfer rate.

  How does software change MESH in Gossamer from 10 MB/s to 5 MB/s?
  
  
• thordrake —
  2026-05-18, 3:05 PM
  I don’t know about others but I do know the Linux kernel features a setting to govern how fast MESH transfers go.
  
  
• DBJ314 —
  2026-05-18, 3:11 PM
  It looks like the SyncPeriod field within SyncParms register. The SyncPeriod field contains the period of the Req or Ack pulse when the MESH controller is in synchronous data transfer mode. The value must be adjusted to match the SyncPeriod time agreement in the SDTR messages. Although the ANSI SCSI specification allows resolution down to 4 ns, the driving software must negotiate a period that is acceptable to both the controller and the target device. A value of 0 indicates 10 MB per second, and 3 indicates 5 MB per second. The equation for determining the period of the synchronous Ack signal is (4*clk + 2*clk*SyncPer) where clk represents one MESH Clk period and SyncPer is the value in the lower nybble of the SyncParms register. Fast synchronous operation is a special case, where 0 means 100 ns.
  
  Quoting from 4.4.12.2 SyncPeriod Field of Macintosh Technology in the Common Hardware Reference Platform
  
  
• joevt —
  2026-05-18, 3:27 PM
  DingusPPC does have some SDTR code, but it doesn't parse any of the info. linux/drivers/scsi/mesh.c has a add_sdtr_msg function where the third byte is set to mesh_sync_period/4 Would be nice for DingusPPC to log the SDTR info so we can see if Gossamer is set to 10 MB/s or 5 MB/s.

 

[Phipli]

I don't think MESH or CURIO has SCSI chips used in Power Macs has a register for SCSI speed.

Assuming it inherited the 53CF96 registers, it should have. The 53CF96 has speed related registers.

https://bitsavers.trailing-edge.com/components/ncr_symbios/scsi/53CF94/53CF94_96-2_Fast_SCSI_Controller_Data_Manual_Apr1993.pdf

Hum, actually, there should probably be a fast SCSI setup sequence in SuperMario, because of the 8100? If they got that far. I feel like I looked before and there was something.