Introducing ZuluSCSI Blaster - now with More Cowbell!

[rabbitholecomputing]

Just over two and a half years ago, Rabbit Hole Computing developed and brought to market the first RP2040-based SCSI emulator, which represented our second-generation ZuluSCSI. Since then, we've been hard at work, implementing support for the new Raspberry Pi Pico 2 and Pico 2 Wireless, which was accomplished late in 2024. This laid the groundwork for supporting the RP2350A's big brother, the RP2350B, which adds another 18 GPIO pins, compared to the RP2350A. This additional hardware capability allows the ZuluSCSI Blaster to function more efficiently while also allowing us to introduce features that have been absent from previous SCSI hardware emulation devices.

Released a week ago, ZuluSCSI Blaster is an advanced SCSI storage emulator and is powered by the Raspberry Pi Foundation's larger and more-versatile RP2350B microcontroller. At launch, ZuluSCSI Blaster does not have built-in Wi-Fi or networking functionality, however it will in the future via an expansion board.

ZuluSCSI Blaster features

• USB-C connector
• 16-bit stereo CD Audio playback emulation via dedicated i2s header. This requires an optional $5 plug-in DAC board.
• Support for ROM drives of up to 15.8 MB in size.
• Expansion header with six GPIOs for future add-on functionality.
• Up to 18 megabytes/second read speeds, 11MB/sec write speeds
• Support for 8-bit narrow Ultra SCSI (20MB/sec) timing, as well as SCSI-1 and SCSI-2
• SCSI Termination is DIP-switch controlled
• Firmware upgrade simplicity; As easy as placing a file on the SD card
• Highly configurable using a text-based ini file, ZuluSCSI.ini
• External activity LED pin header for attaching remote activity LED
• Designed to be powered via SCSI termination power when provided by the host
• Initiator mode support for both reading from and writing to Hard Drives and CD-ROM drives via USB!
• Emulates up to 7 SCSI devices simultaneously, including CD-ROM, Magneto Optical, removable (SyQuest/Jaz-style), and SCSI floppy device types

ZuluSCSI Blaster supports synchronous and asynchronous SCSI transfers, with synchronous read throughput of up to 18 megabytes/second. A sufficiently fast SD card and SCSI controller with Ultra SCSI support is required to achieve maximum throughput.

As always, ZuluSCSI firmware is open-source, and GPLv3-licensed.

 

[LaPorta]

So does that mean that Macs can mount the emulated devices on the SD card as native HFS disks?

 

[rabbitholecomputing]

So does that mean that Macs can mount the emulated devices on the SD card as native HFS disks?

Nope, it absolutely does not mean that. The operating system on the computer still has to be able to understand the filesystem to be able to read/write to it. It isn't magic. That said, with a utility such as HFSExplorer or FuseHFS, you can use the two in tandem to achieve this sort of goal.

 

[LaPorta]

Nope, it absolutely does not mean that. The operating system on the computer still has to be able to understand the filesystem to be able to read/write to it. It isn't magic. That said, with a utility such as HFSExplorer or FuseHFS, you can use the two in tandem to achieve this sort of goal.

Sorry, I will restate: assuming the Mac in question natively supports HFS, will this be able to mount the emulated devices?

 

[Powerbase]

Neat.

 

[adespoton]

Sorry, I will restate: assuming the Mac in question natively supports HFS, will this be able to mount the emulated devices?

Sounds like yes, if FUSE-HFS will enable it.

I like this approach; modular, so you can run a lightweight card and later upgrade with add-ons.

 

[paws]

This looks great. Hope it comes to a European reseller soon.

 

[rabbitholecomputing]

This looks great. Hope it comes to a European reseller soon.

Thanks! We're working on it.

 

[rabbitholecomputing]

This looks great. Hope it comes to a European reseller soon.

Our EU reseller has ZuluSCSI Blasters in stock now.

 

[David Cook]

Just received mine this weekend. I ran some quick performance tests comparing the standard 2022c v1.1 Atmel-based ZuluSCSI vs the new ZuluSCSI blaster and System 7.1.

Note: Ignore seek times as SD cards do not have a drive head that needs to be positioned. Throughput is all that matters.

Here's the IIci with the standard:



Now with blaster. 13% improvement on maximum read, but 48% on write -- and steady.


Here's the IIfx on standard. Hmm. Not as good as the IIci on read?


Here's the IIfx on blaster. About the same? Something appears to cap performance on the IIfx. Not what I expected. I need to look into that. Something is probably wrong with my setup.


Here's the standard on the Quadra 650. Much better than the IIci. Still shaky write performance.


Here's the blaster on the Quadra 650. 23% read improvement and 64% write improvement. Very nice.


The documentation is clear that slower computers are not going to get the same gains as faster computers, because the computer's CPU and memory is the bottleneck. Still, these are really decent numbers.

 

[Realitystorm]

Weird, the IIfx has a max of 3MB/s, the others look like they are hitting their max or close to it https://www.savagetaylor.com/TIL/TA29470.html

 

[zigzagjoe]

Weird, the IIfx has a max of 3MB/s, the others look like they are hitting their max or close to it https://www.savagetaylor.com/TIL/TA29470.html

That's probably an ideal figure if the hardware dma was used. Only A/UX made use of that.

 

[Realitystorm]

That's probably an ideal figure if the hardware dma was used. Only A/UX made use of that.

Good to know. I will be trying this in my LC475 soon to see if I can get close to the 6MB/s theoretical max

"Note (1): The transfer rate of the 53C96 can reach 6MB/sec when using a fast hard drive, provided the cabling is capable of supporting that speed"

 

[rabbitholecomputing]

Just received mine this weekend. I ran some quick performance tests comparing the standard 2022c v1.1 Atmel-based ZuluSCSI vs the new ZuluSCSI blaster and System 7.1.

Since there's never been an Atmel-based ZuluSCSI, can you clarify which model you're specifically referring to? I presume you have a ZuluSCSI V1.1, which used the Gigadevice GD32F205, an improved STM32F205 clone. It's printed on the board.

Also, which firmware version was on the ZuluSCSI Blaster when you ran the above tests? It's written to the log file.

 

[David Cook]

Gigadevice GD32F205, an improved STM32F205 clone

You're correct. Old eyes, I'm afraid.

Also, which firmware version was on the ZuluSCSI Blaster when you ran the above tests? It's written to the log file.

[10ms] FW Version: 25.03.19-release Mar 19 2025 16:57:18

Doesn't seem like the newer firmware has any changes related to performance. Happy to update it if you want.

 

[rabbitholecomputing]

[10ms] FW Version: 25.03.19-release Mar 19 2025 16:57:18

Doesn't seem like the newer firmware has any changes related to performance. Happy to update it if you want.

Given the host/controller-side speed/throughput limitations, It may or may not, but it may be interesting to see the https://github.com/ZuluSCSI/ZuluSCSI-firmware/releases/tag/v2025.04.10 numbers and see how they contrast with the previous batch, using the same SD card.

FWIW, another ZuluSCSI Blaster user observed and self-reported the following throughputs under FreeBSD 14.2 on an x86_64 PC.

 

[NJRoadfan]

Quadras are going to get a bit of a boost in transfer speeds as they have newer SCSI chips along with SCSI Manager 4.3 drivers.

 

[David Cook]

umbers and see how they contrast with the previous batch, using the same SD card.

Okay. I upgraded the firmware. I repeated the tests and they produced the same results. No big deal. I'm happy with the performance improvements.

Aside: I tested the IIfx with ZuluSCSI and MacSD with even a different video card and a different IIfx, across System 7.0.1, 7.1, 7.5, and 7.5.5, and I got the same results.

I'm beginning to think the IIfx actually has a sub-par SCSI subsystem. Check out lowendmac benchmarks between a IIsi and a IIfx on Speedometer 4.02, 128KB disk cache, System 7.5.5, Quantum ProDrive LPS HD S Setup 7.3.5.

IIsi: 0.24 cpu, 0.30 graphics (4-bit), 0.81 disk, 0.55 math
IIfx: 0.71 cpu, 0.45 graphics (8-bit), 0.74 disk, 2.99 math