core 4.0: 256 KB for the mods (Digitakt mk1)

The core for the Digitakt mk1, version 4.0, built from mods/core at a31fc89 (#95). This is a pre-release. The page and the apps keep taking their built-in cores from the latest release (v0.4.0) until the next one. Once the mod shop lists these two files, the web page and the kit take them from here.

file	OS
core-4.0.elemod	1.53
core-4.0-os1.54.elemod	1.54

What 4.0 is: core 3.0 with twice the RAM for the mods. It has the same code, sites, events, tables and exports as 3.0, and the linker lays the mods' code, tables and variables out from 0x47BC0000 to 0x47C00000: 256 KB in place of 128 KB.

• The space it uses: the whole gap between the sample pool's end and the audio input ring. Nothing else in the Digitakt's DDR is free, so 256 KB is as far as it goes.
• Machine mods built for 3.0 (machine-pages 1.1, DT-FM 1.2) link with it unchanged.

Which core a build takes: the newest core of the oldest major line that is new enough for the selection and whose RAM holds its mods.

• A selection over 128 KB takes 4.0, though its mods would take 2.1 or 3.0.
• A selection that fits keeps 2.1 or 3.0, and its bytes.

Checked in digikit's emulator with 4.0, digihealth 1.0 and a 200 KB test mod (207 KB in all), against stock 1.53 and 1.54:

• Every stage of the firmware check passes, and all nine screens are identical.
• The test mod's 200 KB, at 0x47BC1248–0x47BF1F88, are filled and read back right through thousands of UI ticks while the pattern plays.
• The same set is refused beside the released 2.1 or 3.0, and the message names 4.0.

The emulator doesn't model the sampler's audio input, which writes the ring just above the area: sampling is the thing to try on a unit.