How to enable Ultra SCSI support on ZuluSCSI RP2040/Pico

As of firmware revision v2024.12.03, there is preliminary/beta-grade support for synchronous transfer rates above 10MB/second. Your SCSI controller must support this. All classic 68K and PowerPC Macintosh computers do not contain a built-in SCSI controller that is capable of supporting SCSI at speeds of above 10 megabytes per second.

In order to achieve this, a ZuluSCSI RP2040 or ZuluSCSI Pico is required. ZuluSCSI V1.x hardware is not capable of supporting these extended transfer modes at this time.

In order to enable support for 20MHz Ultra SCSI, two parameters must be set in a zuluscsi.ini file, which must be present in the root directory of the SD card.

[SCSI]
SpeedGrade=TurboMax
MaxSyncSpeed=20

With a ZuluSCSI RP2040 or Pico, the first parameter instructs the firmware to overclock the RP2040 to 250MHz, from the default clock rate of 133MHz. No active or passive cooling is needed in our testing.

Performance

With Ultra SCSI mode enabled, maximum read throughput of approximately 17.5MB/sec is achievable, which represents an 80% improvement in read performance. Maximum write speeds of up to 11MB/second have been observed.