# MAME local edits

`mame-local-edits.patch` is the complete set of changes this project makes to
upstream MAME. It is **50 lines across four files**, and it is the whole reason a
MAME tree is needed at all:

| file | change |
|---|---|
| `src/devices/cpu/tms34010/tms34010.cpp` | `REG_REFCNT` advances per cycle — required for the level-1 VIDEO MEMORY test |
| `src/devices/machine/mc68681.cpp` / `.h` | the overrun error is latched on the **start bit** of the overrunning character, per the SCN2681 datasheet |
| `src/mame/mame.lst` | adds the `vt1200` driver entry |

Each change carries an **inline revert note at the site**, and the rationale for
each is in `harness/mame/DUART_REPORT.md`. One further proposed edit (TxRDY
assertion timing) was **refuted** by the fitted part's datasheet and is not here.

## Applying it

```sh
git clone --depth 1 --branch mame0289 \
    https://github.com/mamedev/mame.git /home/arti/code/k-space/mame0289
git -C /home/arti/code/k-space/mame0289 am \
    /home/arti/code/k-space/vt1200/patches/mame-local-edits.patch
harness/mame/build.sh          # symlinks the driver in and builds
```

`git am` preserves the commit message and author. If it does not apply cleanly
because upstream moved, `git apply -3` will fall back to a three-way merge.

**Note the clone is at a _tag_, not a branch.** `--branch mame0289` where
`mame0289` is a tag leaves a **detached HEAD**, so commit before you check
anything else out — otherwise edits are discarded.

## Why a patch as well as a repo

The MAME tree **is** now pushed as a full repository — `origin` is
`git@git.k-space.ee:arti/mame0289.git`, and our commit sits on branch
**`vt1200-local`** there. Getting there needed `git fetch --unshallow` first
(99,645 commits, `.git` 1.9 GB, ~3 minutes) because the server rejects shallow
updates:

```
! [remote rejected] vt1200-local -> vt1200-local (shallow update not allowed)
```

`receive.shallowUpdate` is off on that server, and the clone was `--depth 1`
pinned at a tag, so no push from it was accepted until it was unshallowed.
`git config receive.shallowUpdate true` on the server would avoid the unshallow
for anyone repeating this.

This patch is kept anyway, for three reasons:

* it is the **complete change in 50 lines** — reviewable in a diff, where a
  1.9 GB repository is not;
* it **reproduces the tree without a full clone**, which matters on a fresh
  machine or a slow link;
* it is the **record of what this project changes about upstream MAME**, and
  every claim about those changes lives beside the driver rather than in a
  repository's history.

Note the branch name is `vt1200-local`, not `master`. If the forge's default
branch is still `master` and therefore empty, set `vt1200-local` as the default
so the repository opens on something.