Tiny SCSI Emulator

More work on Ethernet support last night. The W5100 raw socket code is in place, and the Cabletron EA412 driver attempts to load on the Macintosh SE. Unfortunately the Cabletron driver crashes (hard) and prevents MacOS from booting further.

The command sequence thus far is:

Inquiry
Inquiry
Get MAC Address
Set Protocol
Set Multicast
<Crash>

Sometimes I don't even see the Set Protocol command.

My next steps will be to try it under NetBSD, and to install macsbug on the SE so I can try to see where the Cabletron driver is crashing.

Over Thanksgiving I was able to dedicate a couple of days to development and testing of firmware revisions and some hardware revisions to get basic disk commands, DMA, and partitioning working. Currently the disk emulation is maxing out the SCSI PHY with plenty of room for growth on the SDHC bus. Future hardware revisions will likely be based on later SCSI PHY controllers which should increase speeds to match the limits of the SDHC socket on the Teensy 3.5.

The current revision hardware manages 16MB/s between the microsd card and Teensy RAM, resulting in about 7MB/s data rate when copying between partitions on the card using the firmware console. FATfs in the firmware is much slower (used to backup and restore partition images) at around 600KB/s and likely to be an improvement goal further down the line.

DMA to/from the host results in upto 1.3MB/s with the current PHY.

Emulation of SCSI Ethernet adapters has been prototyped out in the current firmware, needing the attachment of a SPI interface ethernet controller without a TCP/IP stack. Optical drive emulation will be added in the future.