greg.ewingIn an effort to make the microcode source more readable, I added the ability to define named constants to the microassembler. They can be referenced anywhere in the source file, and they simply get textually expanded into their definitions.
This is what the microcode looks like now. While still not exactly crystal clear to the uninitiated, I hope you'll agree it's better than it was.
AddressBits := 10 DataBits := 32 # Unused field values - = 0 -- = 00 --- = 000 ---- = 0000 # Single bit values SHS = 1 # Shift S Register EOI = 1 # End of Instruction CMX = 1 # Complement X ODD = 1 # MSW of double word memory reference MSW = 1 # Most significant word LSW = 1 # Least significant word SS1 = 1 # Shift S Register by one bit WMEM = 1 # Write memory INCMS = 1 # Increment multiplication step counter MMSW = 1 # MSW of multiplicand MLSW = 1 # LSW of multiplicand # WRF values WAC = 10 # Write Accumulator WMR = 01 # Write Multiplier Register WPR = 11 # Write Product Register # XSEL values X0 = --- # Zero XAC = 100 # Accumulator XMEM = 010 # Memory XMUL = 110 # S Register * Nultiplier XPR = 001 # Product Register # YSEL values Y0 = 00 # Zero YAC = 10 # Accumulator YAND = 01 # Multiplier & Memory YPR = 11 # Product Register, or zero if first multiplication step # Carry control values (CY1, CYP) CY0 = 00 CY1 = 10 CYP = 01 # MISC values FETCH = 100 # Instruction fetch RSH = 110 # Right shift HALT = 001 # Halt at end of instruction # OPCODE L STAT : SHS EOI RFA XSEL CMX YSEL CARRY WRF ODD SS1 MSW LSW MMSW MLSW WMEM MISC INCMS UBCOND UBADDR # Fetch xxxxx x 0000 : SHS - -- --- - -- -- -- - - - - - - - FETCH - --- ---- # A - Add 11100 0 0001 : - EOI 11 XMEM - YAC CY0 WAC - - MSW LSW - - - --- - --- ---- 11100 1 0001 : - - 01 XMEM - YAC CY0 WAC - - - LSW - - - --- - --- ---- 11100 1 0010 : - EOI 11 XMEM - YAC CYP WAC ODD - MSW - - - - --- - --- ---- # S - Subtract 01100 0 0001 : - EOI 11 XMEM CMX YAC CY1 WAC - - MSW LSW - - - --- - --- ---- 01100 1 0001 : - - 01 XMEM CMX YAC CY1 WAC - - - LSW - - - --- - --- ---- 01100 1 0010 : - EOI 11 XMEM CMX YAC CYP WAC ODD - MSW - - - - --- - --- ---- # Z - Halt 01101 0 0001 : - EOI -- --- - -- -- -- - - - - - - - HALT - --- ---- # T - Transfer and clear 00101 0 0001 : - EOI 11 XAC CMX YAC CY1 WAC - - MSW LSW - - WMEM --- - --- ---- 00101 1 0001 : - - 01 XAC CMX YAC CY1 WAC - - - LSW - - WMEM --- - --- ---- 00101 1 0010 : - EOI 11 XAC CMX YAC CYP WAC ODD - MSW - - - WMEM --- - --- ---- # U - Transfer without clear 00111 0 0001 : - EOI 11 XAC - Y0 CY0 -- - - - - - - WMEM --- - --- ---- 00111 1 0001 : - - 01 XAC - Y0 CY0 -- - - - - - - WMEM 00111 1 0010 : - EOI 11 XAC - Y0 CY0 -- ODD - - - - - WMEM --- - --- ---- # H - Load Multiplier 10101 0 0001 : - - 01 X0 - Y0 CY0 WMR - - - LSW - - - --- - --- ---- 10101 0 0010 : - EOI 11 XMEM - Y0 CY0 WMR - - MSW - - - - --- - --- ---- 10101 1 0001 : - - 01 XMEM - Y0 CY0 WMR - - - LSW - - - --- - --- ---- 10101 1 0010 : - EOI 11 XMEM - Y0 CY0 WMR ODD - MSW - - - - --- - --- ---- # C - Collate 11110 0 0001 : - EOI 11 XAC - YAND CY0 WAC - - MSW LSW - - - --- - --- ---- 11110 1 0001 : - - 01 XAC - YAND CY0 WAC - - - LSW - - - --- - --- ---- 11110 1 0010 : - EOI 11 XAC - YAND CY0 WAC ODD - MSW - - - - --- - --- ---- # L - Left shift 11001 x 0001 : - - 00 XAC - YAC CY0 WAC - - - LSW - - - --- - --- ---- 11001 x 0010 : - - 10 XAC - YAC CY0 WAC - - - - - - - --- - --- ---- 11001 x 0011 : - - 01 XAC - YAC CY0 WAC - - - - - - - --- - --- ---- 11001 x 0100 : - EOI 11 XAC - YAC CY0 WAC - SS1 MSW - - - - --- - 100 1000 # R - Right shift 00100 x 0001 : - - 00 XAC - Y0 CY0 WAC - - - LSW - - - RSH - --- ---- 00100 x 0010 : - - 10 XAC - Y0 CY0 WAC - - - - - - - RSH - --- ---- 00100 x 0011 : - - 01 XAC - Y0 CY0 WAC - - - - - - - RSH - --- ---- 00100 x 0100 : - EOI 11 XAC - Y0 CY0 WAC - SS1 MSW - - - - RSH - 100 1000
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I see very familiar concepts in your microassembler - check out my attempt to build a microcode compiler and use it to implement a CPU https://hackaday.io/project/172073-microcoding-for-fpgas
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Looks interesting! Playing with FPGAs is something I want to try in the future too.
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Fascinating technology and for hobbyist extra fun as it can be combined so easily with computing retrotechnology. However I wanted to keep the control unit schema and microcode structure so simple that it can be built with few classic ICs too.
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