ND-120 device address map

Full path: Verilog/docs/device-address-map.md

Every ND-BUS device in this tree: its IOX address, ident code, interrupt level and where the registers are defined. All addresses are OCTAL - that is the ND convention and mixing it up with hex is a recurring source of wasted time (a testbench written with 16'h504 instead of 16'o504 looks like a dead controller).

The values below are read out of the RTL parameters, not from memory or from a manual, so they cannot drift from what the hardware actually decodes.

The map

Device	IOX base	Ident	Level	Module	Backing store
Paper tape reader, device 400	400	2	12	ND-BUS-DEVICES/TAPE-400/circuit/ND_TAPE_400.v	BOOT.TAP (Tang) / BOOT.BPUN
Winchester disc (ST506/3041)	500	1	11	ND-BUS-DEVICES/WINCHESTER/circuit/ND_WINCHESTER.v	WD0.IMG, WD1.IMG
SMD disc controller, 15 MHz	1540	17	11	ND-BUS-DEVICES/SMD/circuit/ND_SMD.v	SMD0.IMG .. SMD2.IMG
Floppy, DMA (3112)	1560	21	11	ND-BUS-DEVICES/FLOPPY-DMA/circuit/ND_FLOPPY_DMA.v	FLOPPY1.IMG, FLOPPY2.IMG
Floppy, PIO (3106, older)	1560	21	11	ND-BUS-DEVICES/FLOPPY/circuit/ND_FLOPPY_PIO.v	same

The two floppy cores share address 1560, ident 21 and level 11 on purpose: they are the same device slot at two different controller generations, and only one is built into any given configuration.

Boot / mass-load commands

The console command that loads from each device. The leading digits are the device address; bit 13 (the leading 2) selects MASS storage load rather than the byte-stream (BPUN) load.

Command	Meaning
400$	load a BPUN byte stream from the paper tape reader
1560&	floppy, stream load (BPUN) - the working floppy boot
21560&	floppy, MASS load - not implemented on either side
500&	Winchester, stream load - this card does not serve it
20500&	Winchester, MASS load - the SINTRAN boot path
1540&	SMD, stream load

Disc geometry

The Winchester and SMD are within 0.5% of the same capacity with completely different geometries (72 vs 90 sectors per cylinder), which makes them easy to confuse and impossible to substitute. Full table, where the parameters live, and how to sanity-check them against a running machine: Verilog/ND-BUS-DEVICES/README.md, section "Disc geometry - Winchester vs SMD".

Register layouts

Each controller's own header block is the authority for its registers, and each cites the manual section it was transcribed from:

Device	Manual	Registers documented in
Winchester	ND-11.015.01 sec 2.1, 3.1-3.5, 4.1	ND_WINCHESTER.v header
SMD	ND-11.020.01 sec 2.5	ND_SMD.v header
Floppy DMA	ND-11.021.01 sec 3.1-3.9	ND_FLOPPY_DMA.v header, plus docs/floppy-3112-register-spec-ND-11.021.md
Paper tape	(no controller manual - modelled on the C reference)	ND_TAPE_400.v header

Storage failure reporting

All four controllers map SD-FAT failures onto status bits their own manuals define. The reason codes and the full per-controller mapping table are in Verilog/SD-FAT/circuit/nd_storage_status.vh.

The paper tape reader is the exception: it has no error bit anywhere in its four registers, so it stays silent (indistinguishable from end of tape to the guest) and publishes the reason on the TDISK_FAULT / TDISK_ERR_CODE diagnostic seam instead. The reasoning is written out in ND_TAPE_400.v.

Keeping this file honest

The table is generated from the RTL. To re-derive it after adding a device:

cd Verilog
for f in ND-BUS-DEVICES/*/circuit/ND_*.v; do
  n=$(basename "$f" .v)
  b=$(grep -oE "BASE_ADDR *= *16'o[0-7]+"  "$f" | head -1 | grep -oE "[0-7]+$")
  i=$(grep -oE "IDENT_CODE *= *16'o[0-7]+" "$f" | head -1 | grep -oE "[0-7]+$")
  l=$(grep -oE "INT_LEVEL *= *4'd[0-9]+"   "$f" | head -1 | grep -oE "[0-9]+$")
  [ -n "$b" ] && printf "%-22s base=%-8s ident=%-8s level=%s\n" "$n" "$b" "$i" "$l"
done