Copyright 2016, 2022 Eric Smith spacewar@gmail.com
wd100x development is hosted at the wd100x Github repository.
Western Digital's earliest hard disk controllers were board-level products based on the Signetics 8X300 or 8X305 bipolar microprocessors. They supported up to four drives with the ST506 interface (5.25-inch) or SA1000 interface (8-inch).
The 8X300 was chosen because, as a bipolar processor, it was much faster than the contemporary MOS microprocessors. Operating from an 8.0 MHz crystal, instruction execution time is 250 ns.
The 8X300 uses 16-bit instructions, but the WD1000 and WD1001 use 24-bit wide instruction memory in the form of three 8-bit wide bipolar PROMs. The additonal eight bits are used to provide I/O port addressing in parallel with instruction execution.
The original WD1000 was 8X300-based and used CRC error detection. There were two main versions of WD1000 firmware, using different sized PROMs. The "small" version used 512-byte bipolar PROMs, and the "large" version used 1024-byte bipolar PROMs. The small firmware only supported a fixed sector size, which could be hard-coded as 128, 256, or 512 bytes. The large firmware allows the sector size to be selected by the host.
Later WD1000 boards used the 8X305, but the firmware does not take advantage of the 8X305 enhancements.
The later WD1001 was 8X305-based, used 32-bit ECC on the sector data fields, always used "large" firmware, and supported configurable sector size. The WD1001 firmware does not take advantage of the 8X305 enhancements, so substituting an 8X300 should work just as well.
The WD1000 host interface had a "task file" of eight registers, which was used with minor changes by WD1010 and WD2010 hard disk controller chips, the IBM PC/AT disk controller, and later, with more substantial changes, by the ATA (IDE) disk interface.
The assembler syntax used does not match any existing 8X300 assembler, including Signetics MCCAP. This assembly source code has not been assembled for verification against the actual WD1000 PROM chips.
The source code was originally derived from a disassembly produced by s8x30x.
This program is free software: you can redistribute it and/or modify it under the terms of version 3 of the GNU General Public License as published by the Free Software Foundation.
This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
You should have received a copy of the GNU General Public License along with this program. If not, see http://www.gnu.org/licenses/.