BlueSCSI firmware and initial README

README.md

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+VAXstation 2000 SCSI Patched ROMs
+=================================
+
+The VAXstation 2000 is a fantastic little "shoe box" VAX computer. A little
+slow maybe but a great entry to the wider world of DEC's VAX computers.
+However it is somewhat lacking in one area: storage. It has one (optional)
+internal hard drive (mine came with a 150MB RD54) and one (optional)
+external hard drive - both of the MFM variety. That's not a big amount of
+storage, and old MFM drives are as you probably know prone to stiction and
+bad blocks, if they even work at all. 
+
+The VAXstation 200 does have a SCSI interface, however it was only intended
+to be used with the optional external TZK50 tape drive, and as such has never
+had any real support for adding hard drives, and it certainly cannot boot
+from a SCSI hard drive even if the operating system supported accessing one.
+
+But all is not lost. An experimental patch set for the VAXstation 200 was
+created (but never officially released) to add full SCSI support to both the
+internal ROMs and to VAX/VMS, but only one specific version. Which is what
+we have here.
+
+Using the patches is not the easiest thing in the world, since you need
+an already working installation of VAX/VMS 5.5-2 (yes, that exact version)
+in order to run the patches. And if you don't have a working hard drive
+to operate the VAXstation on, how are you going to get a working installation?
+The answer is to net-boot it with a VAX cluster. But doing so makes it
+rather hard to then make a standalone image. But it can be done with a bit
+of shoehorning. Which thankfully we have done for you. In the releases
+section you will find a set of BlueSCSI hard drive images that should allow you
+to boot a VMS installation (dka200) that is ready to be completed with
+your own details, along with the installation source files (dka300) which
+the installation will ask you for.
+
+Using it
+--------
+
+In short:
+
+1. You need to upgrade your ROMs using the four ROM images (b1-b4) in the ROMs
+   directory. You will need four new 64kB EPROMs to burn the images to then
+   replace the ROMs on your VAXstation 2000's motherboard.
+
+2. Connect the BlueSCSI to the SCSI bus (important: see belo), making sure to enable termination if
+   you don't have the TZK50 tape drive attached or an external terminator.
+
+3. Boot from the dka2 device:
+
+```
+>>> boot dka2
+```
+
+4. Complete the installation following the on-screen prompts. When it asks for
+   the installation media tell it `dka300`.
+
+5. Install the patched binaries into the installed os:
+
+```
+$ mount/over=id dka300
+%MOUNT-I-MOUNTED, VMS552       mounted on _DKA300:
+$ set def dka300:[scsi.bin]
+$ @install
+```
+
+Now the long version:
+
+Installing the ROMs is pretty straight forward. There's 4 EPROM chips on the motherboard
+which need replacing.
+
+{image here}
+
+Note the order, as marked on these ROMs.
+
+The BlueSCSI (which should be a BlueSCSI II Desktop version so you get the proper 50 pin
+IDC connector) will not work with the VAXstation out of the box due to the VAXstation
+being from the dawn of SCSI and not working in quite the same way as other systems
+(the joys of old computers...) so the BlueSCSI will need to be modified in order to work.
+
+The problem here is that the SEL pin and RST pin of the SCSI are weakly tied together inside the
+BlueSCSI, so when the RST pin is asserted by the SCSI initiator the SEL pin gets pulled
+low, which shouldn't happen. Most things don't care - but the VAXstation does, and when that
+happens it just gives up trying to do anything on the SCSI bus ever again.  So we need
+to separate those two signals. This needs some careful SMD rework.
+
+1. Remove the resistor R61. This is the resistor that ties the two signals together.
+2. Connect the left hand pad of R61 to the pin GPIO17 of the Raspberry Pi Pico. This
+   gives the MCU direct control over the SEL pin.
+3. Install modified firmware into the Pi Pico which moves the SEL functionality to
+   GPIO 17.
+
+This modification uses one of the pins that was used for I2C for the SEL pin, so you will
+no longer be able to use the I2C connector on the BlueSCSI.