AWS Turbo disk controller board
This is a reverse engineering project. The AWS was an 8088/8086 based computer made by Convergent Technologies in the mid 1980's. Some models had the AWS Turbo disk controller. This handled a 5.25 inch floppy and an MFM hard drive.
It was based on a Signetics N8x300 processor. This project is fundamentally a disassembly and analysis of the firmware for this processor. The purpose of this is a deeper understanding of the AWS hard drive controller, along with general fun and games.
The bulk of the "action" is aws.dis. This is a disassembly, heavily annotated by comments I am adding as I work to understand the firmware. I update this regularly as I study and learn more.
The AWS itself had 3 major boards. A so called "motherboard" which mostly did signal routing, a CPU board (2 versions, one with an 8088, the other with an 8086), and a disk controller board (either a FDC controller, or the HDC controller we are studying in detail here). Note that the HDC controller also handled a floppy.
Schematics are available for all of these boards in the technical manual. Not for the motherboard though, you just get tables of wire lists.
P13 was the MFM disk connector (actually a pair of connectors) for the hard drive. P11 and P12 were the connectors to floppy drives (you could have two).
The HDC controller had 2 big edge connectors. P10 was a 50 pin connector and was a sort of bus between it and the CPU card. P9 was an 80 pin connector and carried most (but not all) of the drive signals.
A note on the disassembler. It is written in python and is here as a single file with the name 8x300_dis. I did not write this. This is my mildly hacked version of s8x30x by Eric Smith and still bears his copyright. My hacking amounted to lumping all the source files into one, and adding some IV bus definitions specific to the AWS controller.
https://github.com/brouhaha/s8x30x
A note on bit order. All of the Signetics 8x300 series documents use an old convention for numbering bits. Namely the MSB is bit 0 and the LSB is bit 7 (in an 8 bit word anyway). The modern convention is just the opposite. The disassembler I used uses the modern convention. So when you see something like sriv[7] the assembly is accessing the MSB not the LSB. This all makes sense to the modern mind and the only time you need to take care is when you look at the old datasheets (and the schematics).