nullsound: new NSS opcode to simulate auto-envelope

Furnace has a feature that reconfigures the SSG envelope based
on the current note's frequency and a configurable quotient
numerator/denominator. This maps into the YM2610's envelope
register.
We don't want to do math on the Z80 at runtime, so we have
to simulate this feature by precomputing the quotient prior
to playing the note at runtime.

Add a new opcode SSG_ENV_PERIOD that is inserted automatically
by nsstool.py in a new compilation pass.
This requires nsstool to know the autoenv configuration for the
instrument in use, so make nsstool parse the instrument section
of the Furnace module before generating NSS data.

nullsound/nss-ssg.s

@@ -806,3 +806,28 @@ _on_post_s1:
         ld      a, #1
         ret
 
+
+;;; SSG_ENV_PERIOD
+;;; Set the period of the SSG envelope generator
+;;; ------
+;;; [ hl ]: fine envelope period
+;;; [hl+1]: coarse envelope period
+ssg_env_period::
+        push    bc
+
+        ld      b, #REG_SSG_ENV_FINE_TUNE
+        ld      a, (hl)
+        inc     hl
+        ld      c, a
+        call    ym2610_write_port_a
+
+        inc     b
+        ld      a, (hl)
+        inc     hl
+        ld      c, a
+        call    ym2610_write_port_a
+
+        pop     bc
+
+        ld      a, #1
+        ret

nullsound/stream.s

@@ -200,6 +200,7 @@ nss_opcodes:
         .dw     ssg_note_off
         .dw     ssg_vol
         .dw     fm_vol
+        .dw     ssg_env_period
 
 
 

tools/nsstool.py

@@ -24,7 +24,7 @@
 import zlib
 from dataclasses import dataclass, field, astuple, make_dataclass
 from struct import pack, unpack_from
-from furtool import binstream, load_module, read_module
+from furtool import binstream, load_module, read_module, read_samples, read_instruments
 
 VERBOSE = False
 
@@ -244,6 +244,7 @@ def register_nss_ops():
         ("s_stop"  , ),
         ("s_vol"   , ["volume"]),
         ("fm_vol"  , ["volume"]),
+        ("s_env"   , ["fine", "coarse"]),
         # reserved opcodes
         ("nss_label", ["pat"])
     )
@@ -593,6 +594,62 @@ def compact_ctx(nss):
     return out
 
 
+def simulate_ssg_autoenv(nss, ins):
+    semitones = [ "C", "C#", "D", "D#", "E", "F", "F#", "G", "G#", "A", "A#", "B" ]
+    freqs = [
+        [  32.7 ,    34.65,    36.71,    38.89,   41.2 ,   43.65,   46.25,   49.0 ,   51.91,   55.0 ,   58.27,   61.74],
+        [  65.41,    69.3 ,    73.42,    77.78,   82.41,   87.31,   92.5 ,   98.0 ,  103.8 ,  110.0 ,  116.5 ,  123.5 ],
+        [ 130.8 ,   138.6 ,   146.8 ,   155.6 ,  164.8 ,  174.6 ,  185.0 ,  196.0 ,  207.7 ,  220.0 ,  233.1 ,  246.9 ],
+        [ 261.6 ,   277.2 ,   293.7 ,   311.1 ,  329.6 ,  349.2 ,  370.0 ,  392.0 ,  415.3 ,  440.0 ,  466.2 ,  493.9 ],
+        [ 523.3 ,   554.4 ,   587.3 ,   622.3 ,  659.3 ,  698.5 ,  740.0 ,  784.0 ,  830.6 ,  880.0 ,  932.3 ,  987.8 ],
+        [1047.0 ,  1109.0 ,  1175.0 ,  1245.0 , 1319.0 , 1397.0 , 1480.0 , 1568.0 , 1661.0 , 1760.0 , 1865.0 , 1976.0 ],
+        [2093.0 ,  2217.0 ,  2349.0 ,  2489.0 , 2637.0 , 2794.0 , 2960.0 , 3136.0 , 3322.0 , 3520.0 , 3729.0 , 3951.0 ],
+        [4186.0 ,  4435.0 ,  4699.0 ,  4978.0 , 5274.0 , 5588.0 , 5920.0 , 6272.0 , 6645.0 , 7040.0 , 7459.0 , 7902.0 ]
+    ]
+    out = []
+    s_ctx_map = {s_ctx_1: 0, s_ctx_2: 1, s_ctx_3: 2}
+    s_ctx = 0
+    s_is = [-1, -1, -1]
+    s_autoenv = [False, False, False]
+    s_period = [-1, -1, -1]
+    for op in nss:
+        if type(op) == wait_b:
+            s_ctx=0
+            out.append(op)
+        elif type(op) == s_macro:
+            if s_is[s_ctx] != op.macro:
+                s_is[s_ctx] = op.macro
+                # False if autoenv isn't defined
+                s_autoenv[s_ctx]=ins[op.macro].autoenv
+                s_period[s_ctx]=-1
+                out.append(op)
+        elif type(op) in s_ctx_map.keys():
+            s_ctx = s_ctx_map[type(op)]
+            out.append(op)
+        elif type(op) == s_note:
+            autoenv=s_autoenv[s_ctx]
+            if autoenv:
+                o=(op.note>>4)&0xf
+                n=op.note&0xf
+                notefreq = int(freqs[o-1][n])
+                num, den = autoenv
+                period = ((125000//notefreq)*den//num)//16
+                # only generate a s_env opcode if the last
+                # note played on this channel differred
+                if s_period[s_ctx] != period:
+                    s_period[s_ctx] = period
+                    fine, coarse = period&0xff, (period>>8)&0xff
+                    out.append(s_env(fine, coarse))
+            s_ctx+=1
+            out.append(op)
+        elif type(op) == s_stop:
+            s_ctx+=1
+            out.append(op)
+        else:
+            out.append(op)
+    return out
+
+
 def remove_unreferenced_labels(nss):
     if isinstance(nss[-1], nss_loop):
         order = nss[-1].pat
@@ -689,6 +746,8 @@ def main():
     dbg("Loading Furnace module %s"%arguments.FILE)
     bs = load_module(arguments.FILE)
     m = read_module(bs)
+    smp = read_samples(m.samples, bs)
+    ins = read_instruments(m.instruments, smp, bs)
     p = read_all_patterns(m, bs)
 
     dbg("Convert Furnace patterns to unoptimized sequence of NSS opcodes")
@@ -707,6 +766,9 @@ def main():
     dbg(" - remove CTX opcodes if they keep the current context unchanged")
     nss = compact_ctx(nss)
 
+    dbg(" - look for SSG autoenv macros and insert opcodes to simulate them")
+    nss = simulate_ssg_autoenv(nss, ins)
+
     dbg(" - compute label offset when LOOP opcode is used")
     nss = compute_loop_offset(nss)