Ring Modulator — HLE + bytecode
Ring Modulator — HLE reconstruction and DSP bytecode
DSPHLE selector 0x14 · program image prog54_ring_modulator · Preview (topology decoded and reconstructed; most panel→cell role mappings are position-decoded).
carrier oscillator x signal; carrier rate=cell 0x00 MEASURED (~1 kHz).
This page pairs the bytecode the effect runs on the NEC µPD6383GF with the high-level reconstruction that makes it audible in MAME. The reconstruction is not the chip’s microcode — it is a textbook DSP block built from the decoded meaning of that microcode, and reading the two together is how the bytecode is understood (and, in time, driven toward a faithful low-level emulation). See also the signal-flow flowchart.
The bytecode below is the source of truth; the HLE reconstruction is not. The HLE is our best current interpretation and may contain mistakes — where the two disagree, the bytecode wins, and a better HLE should be updated here. This page is the permanent archive of the reference HLE: it is kept here even after the code is eventually removed from the MAME sources.
DSP bytecode (reverse-engineered microprogram)
The disassembled image the chip executes for this effect. Source (regenerable):
dsp/disasm/prog54_ring_modulator.dsm.
; Reverse-engineered disassembly of the KN5000 effects-DSP microcode
; (NEC uPD6383GF), recovered from the original firmware. The microcode is the
; work of its original authors; this is a disassembly for preservation and
; interoperability, and no claim of copyright is made over the disassembled program.
; KN5000 effects-DSP program -- RING MODULATOR
; image rep algo 54 | slots 54 | unit 0 (I-RAM load 84)
; family am | confidence high | 46 words, 6 class-A multiplies (0 named)
; role: ring modulator: audio-rate quadrature AM
; coefficient cursor base 0x00
;
; GENERATED by dsp/tools/gen_dsp_disasm.py -- DO NOT EDIT.
; Put labels/comments in the matching dsp/sym/*.sym; analysis in dsp/algorithms/.
w0 00400008BC ?word 0x00400008BC ; 040.0.00.8BC hi12{?6 res=040} [SPECULATIVE: lo12 bit-11 modifier word + pointer-mode (bit11-family); the base selector/register is OPEN]
w1 000020B1CD ld (p),(p)+11
w2 000020040E ld acc,(p)+0
w3 0212200000 mac.b (p)0,(p)+0 ; mem[p]<-acc, acc=0
w4 002A200000 ?word 0x002A200000 ; 02A.2.00.000 hi12{f31=5 ?5 res=020} [SPECULATIVE (prospective, not measured): SRC 0x00 = mem[ptr]/delay-RAM read]
w5 00002FE1CD ld (p),(p)-2
w6 000020040E ld acc,(p)+0
w7 0212200000 mac.b (p)0,(p)+0 ; mem[p]<-acc, acc=0
w8 0028200000 ?word 0x0028200000 ; 028.2.00.000 hi12{f31=4 ?5 res=020} [SPECULATIVE (prospective, not measured): SRC 0x00 = mem[ptr]/delay-RAM read]
w9 0880130407 dly.r dsc[k],p+48
w10 0092A04200 mac.b c,c+,(p)+4 ; store SUPPRESSED (bit7)
; C-RAM[0x00] (coeff, base 0x00 MEASURED)
w11 00822001C0 mac.b (p),(p)+0
w12 0094A00200 wrap acc,c+ ; acc <- datum(acc) & coef (LFO modulus)
; C-RAM[0x01] (coeff, base 0x00 MEASURED)
w13 0000200447 ?word 0x0000200447 ; 000.2.00.447 hi12{-} [SPECULATIVE (prospective, not measured): SRC 0x11 = ACCB (2nd accumulator)]
w14 0092200700 ?word 0x0092200700 ; 092.2.00.700 hi12{ST f31=1 ?7 res=080} [SPECULATIVE (prospective, not measured): SRC 0x1C = control/mod source into MAC (100% MAC-consumed; LFO in mod fx, envelope/AGC in dynamics) -- NOT LFO-only: present in 19 non-LFO programs (dsp_datapath_fingerprint)]
w15 0000A001D5 ld (p),c+,(p)+0
; C-RAM[0x02] (coeff, base 0x00 MEASURED)
w16 0182200000 mac.b (p)0,(p)+0
w17 0040000C63 ?word 0x0040000C63 ; 040.0.00.C63 hi12{?6 res=040} [SPECULATIVE (prospective, not measured): SRC 0x11 = ACCB (2nd accumulator)]
w18 00006184CD ?word 0x00006184CD ; 000.6.18.4CD hi12{-} [table-lookup idiom, class-6 addr8 = table selector (INFERRED)]
w19 00124011CE ?word 0x00124011CE ; 012.4.01.1CE hi12{ST f31=1} [table-lookup idiom, third word (INFERRED)]
w20 01042FE1CE post (p),(p)-2
w21 0102200000 mac.b (p)0,(p)+0
w22 0000203407 ld.st acc,(p)+3
w23 0092A00200 mac.b c,c+,(p)+0 ; store SUPPRESSED (bit7)
; C-RAM[0x03] (coeff, base 0x00 MEASURED)
w24 00822001C0 mac.b (p),(p)+0
w25 0094A00200 wrap acc,c+ ; acc <- datum(acc) & coef (LFO modulus)
; C-RAM[0x04] (coeff, base 0x00 MEASURED)
w26 0000200447 ?word 0x0000200447 ; 000.2.00.447 hi12{-} [SPECULATIVE (prospective, not measured): SRC 0x11 = ACCB (2nd accumulator)]
w27 0092200700 ?word 0x0092200700 ; 092.2.00.700 hi12{ST f31=1 ?7 res=080} [SPECULATIVE (prospective, not measured): SRC 0x1C = control/mod source into MAC (100% MAC-consumed; LFO in mod fx, envelope/AGC in dynamics) -- NOT LFO-only: present in 19 non-LFO programs (dsp_datapath_fingerprint)]
w28 0000A001D5 ld (p),c+,(p)+0
; C-RAM[0x05] (coeff, base 0x00 MEASURED)
w29 0182200000 mac.b (p)0,(p)+0
w30 0040000C63 ?word 0x0040000C63 ; 040.0.00.C63 hi12{?6 res=040} [SPECULATIVE (prospective, not measured): SRC 0x11 = ACCB (2nd accumulator)]
w31 00006184CD ?word 0x00006184CD ; 000.6.18.4CD hi12{-} [table-lookup idiom, class-6 addr8 = table selector (INFERRED)]
w32 00124011CE ?word 0x00124011CE ; 012.4.01.1CE hi12{ST f31=1} [table-lookup idiom, third word (INFERRED)]
w33 01042FE1CE post (p),(p)-2
w34 0102200000 mac.b (p)0,(p)+0
w35 0880130407 dly.r dsc[k],p+48
w36 00002F4000 nop
w37 000020A1CD ld (p),(p)+10
w38 00002021CE ld (p),(p)+2
w39 0212200000 mac.b (p)0,(p)+0 ; mem[p]<-acc, acc=0
w40 002A200000 ?word 0x002A200000 ; 02A.2.00.000 hi12{f31=5 ?5 res=020} [SPECULATIVE (prospective, not measured): SRC 0x00 = mem[ptr]/delay-RAM read]
w41 00002EF1CD ld (p),(p)-17
w42 000020040E ld acc,(p)+0
w43 0212200000 mac.b (p)0,(p)+0 ; mem[p]<-acc, acc=0
w44 0880160000 dly.w dsc[k],p+96
w45 042810E000 ?word 0x042810E000 ; 428.1.0E.000 hi12{END f31=4 ?5 res=020} [END OF BLOCK, unit 0 -- CALL/RETURN -- and still performs the rest of the word]
HLE reconstruction (MAME, kn5000_tonegen.cpp)
The decode of the bytecode above, rebuilt as audible DSP. Two parts: the parameter refresh
(reads the decoded C-RAM coefficient cells once per update) and the per-sample insert (the
signal processing). Default OFF, behind the DSPHLE research port. Source:
src/mame/matsushita/kn5000_tonegen.cpp.
Parameter refresh (decode the C-RAM coefficients):
const bool ring_hle = (dsphle == 0x14);
double ring_inc = 0.0;
if (ring_hle) { ring_inc = std::clamp(rate_hz(0x00), 20.0, 4000.0) / double(STREAM_RATE); }
Per-sample insert (the reconstructed signal path):
if (ring_hle) // RING MODULATOR: multiply by a carrier oscillator (~1 kHz) -> sidebands
{
const double xl = double(mix_l) / 32768.0, xr = double(mix_r) / 32768.0;
const double c = std::sin(TWO_PI * m_ring_phase);
m_ring_phase += ring_inc; if (m_ring_phase >= 1.0) m_ring_phase -= 1.0;
mix_l = int32_t(std::clamp(xl * c, -1.0, 1.0) * 32767.0);
mix_r = int32_t(std::clamp(xr * c, -1.0, 1.0) * 32767.0);
}