rytm2_mods

rytm-mods-src's Analog Rytm MKII OS 1.73 mods, for OS 1.73 and 1.74 (MrScruff, published with permission), ported one by one to the elemod format so they link with elekloader's core-ar2 and with each other, instead of being patched into code caves at fixed addresses.

From v1.2, euclid-accents, velocity-humanise and voice-dac keep their settings in core-ar2 0.3's mod storage and build for OS 1.74 only; lfo-rnd uses core-ar2's storage too. From v1.3, lfo-rnd 1.2, voice-dac 1.3, euclid-accents 1.2 and velocity-humanise 1.2 reach the parameter pages through core-ar2 0.4's page tables, so they need core-ar2 0.4 (OS 1.74 only), and other mods with pages can link beside them. comp-preview 1.1 lists its preview through core 0.4's page-key lists for the same reason, so a mod can add a page behind COMP too. From v1.4, voice-dac 1.4 (MrScruff's rytm-mods-src 3a98e23: DAC FILTER's knobs follow TYP) needs core-ar2 0.6, whose page functions let a page's knobs follow the selected sound.

No firmware is included: no OS files, sections, dumps or built .syx/.elemod files. The mods name firmware routines by address only (include/ar2-1.73.inc, include/ar2-1.74.inc), and their mod.json sites carry the stock instruction bytes they replace, as elekloader's own mods do.

Layout

How a rytm-mods mod becomes an elemod mod

Rules that matter (elekloader docs/ADAPTING.md): only labels that a site or event names are .globl, and they start with the mod's id; everything else stays local, so two mods never export the same name. port_mod.py adds a prefixed global alias beside each such label, so the stub's own references stay local and assemble as they did in rytm-mods (the hand-ported slice-loop and env-reset-amp rename their entry label instead). A site covers whole stock instructions; the stub re-emits what it displaced, exactly as in rytm-mods. Two mods may never patch the same bytes.

0000-shared is not a mod here: its ~234 bytes are assembled into each mod that calls it (velocity-humanise, lfo-rnd and voice-dac), so every mod stands alone. euclid-accents, velocity-humanise, lfo-rnd and voice-dac keep their settings in core-ar2's mod storage (storage in their mod.json), not in the OS's saved records: euclid-accents 1.1, velocity-humanise 1.1 and voice-dac 1.2 need core-ar2 0.3, which is OS 1.74 only, and lfo-rnd 1.1 needs 0.2 or later. velocity-humanise no longer needs euclid-accents.

The page routines: from core-ar2 0.4, core owns the entries of page_info, page_get_value, param_apply_delta and param_value_text and asks each mod's core_pages and core_params entries in turn (lfo-rnd, voice-dac, euclid-accents, velocity-humanise, by their order), before stock; the four answer for different ids, so the order does not change what they do. Mods that hook deeper in those routines keep their own sites: ctrl-all in param_apply_delta (0x400378c2 on 1.74) and filter-hz in param_value_text. Before core 0.4 the four mods detoured consecutive instructions at each entry, each rejoining at the next mod's jmp, as in rytm-mods, which left no room for a fifth mod with pages.

OS 1.74

Elektron's 1.74 changes only the main OS, and that is 1.73's with code added in two places (Outbox 8's main-output routing): the code after 0x4005702a sits 0x6c further on, after 0x40123e2a 0x1cc, and the data after the code by other amounts. RAM from 0x402ce000 on and the SRAM did not move. Building for 1.74 needs an elekloader that knows the Rytm's 1.74 (its release in the profile, and core-ar2's 1.74 port).

Every mod's 1.73 source is its source of truth. tools/port_os.py (run with both stock files) writes the 1.74 port from it: each firmware address in the include, the sources' code and the sites, moved and checked (see the tool), and each site's stock bytes read from 1.74. It writes nothing if any address fails its check. Run it again after changing a 1.73 source. elekloader builds the port when given the 1.74 stock file, as <id>-<version>-os1.74.elemod.

Checked with both stock files: core-ar2 with all eleven ports, built for each, changes the same instructions at the same (moved) sites, and the mods' code differs only in the firmware addresses it names, each the moved one. A word in the mods' code that holds a 1.73 address whose 1.74 address differs, left unmoved, is a port error: the include once kept two vtable addresses tagged const (ctrl-all's set checks) at their 1.73 values, which made TRK + turn reach only the selected track on 1.74.

Build

You need:

• an elekloader checkout at main with core-ar2 0.6 (irpina/elekloader#179) and the Python 3 it asks for (v1.3 builds with core-ar2 0.4 or 0.5, from irpina/elekloader#155 on);
• ColdFire binutils on PATH (m68k-linux-gnu-as and -ld; on Debian or Ubuntu, apt install binutils-m68k-linux-gnu);
• your own copy of Elektron's stock Analog Rytm MKII OS 1.74 .syx. It is never part of this repository or of anything built from it. (On OS 1.73, v1.0 still has all eleven mods; its own README says which elekloader it builds with. v1.2's lfo-rnd, voice-dac, euclid-accents, velocity-humanise and comp-preview do not link with core 0.4, so v1.3's are needed for it.)

EL=path/to/elekloader                        # the elekloader checkout
R2=path/to/rytm2_mods                        # this repository
STOCK=path/to/Analog-Rytm_MKII_OS1.74.syx    # your stock OS file
OS=-os1.74
cd "$EL"
python3 -m elekloader.sdk.build mods/core-ar2 --stock "$STOCK"
MODS="filter-hz ctrl-all env-reset-amp slice-loop euclid-accents velocity-humanise lfo-rnd
      comp-preview main-rms kit-ab voice-dac"
ARGS=""
for m in $MODS; do
  python3 -m elekloader.sdk.build "$R2/$m" --stock "$STOCK"
  V=$(python3 -c "import json; print(json.load(open('$R2/$m/mod.json'))['version'])")
  ARGS="$ARGS --mod $R2/$m/out/$m-$V$OS.elemod"
done
python3 -m elekloader.patch --stock "$STOCK" --mod mods/core-ar2/out/core-0.6.elemod $ARGS \
    --out rytm-mods.syx --version R2AL --lockfile rytm-mods.lock.json

Leave out any mod you don't want from MODS. Keep rytm-mods.lock.json and pass it again for every later build: it says where each mod's settings live in your projects, kits and sounds, so a build that adds or drops a mod still reads them. (A lost lockfile can be taken back out of the last build with --lockfile-from rytm-mods.syx.) elekloader.patch checks that the selected mods combine before it writes anything. --version is the four characters the unit shows as its OS version. The result is your own firmware file: keep it, and the out/ build folders, out of git and out of any upload.

Status

Every mod on rytm-mods-src main is now ported. "Matches label by label": tools/verify_port.py re-assembles rytm-mods' own code, checks it equals rytm-mods-src's default build ("T2"), then compares each label's instructions with the port's, every address named by its label. For all eleven, in the full build (core-ar2 with every port, as in Build above): every byte it changes in the OS is inside one of the ports' sites, every one of those sites is also patched by rytm-mods' default build (T2), and the bytes sites write T2's bytes exactly. rytm-mods' diagnostic builds (its non-default params and the claims they gate) are not ported.

Licence

GPL-2.0, as rytm-mods-src (LICENSE). The mods are MrScruff's work; the elemod ports keep his code and note every change.