Version 1.5 - QXL.WIN hard disk and 4 MB of RAM (MEGA65 R6)

A QL with a hard disk and 4 MB of RAM. V1.5 adds QXL.WIN support and moves
the QL's main memory into the MEGA65's SDRAM chip.

What's new since V1.01

• QXL.WIN hard disk support (QL-SD). Mount a .win image from the Options
  menu and the QL sees it as win1_ — reading and writing, confirmed on real
  hardware. Needs the QL-SD driver in the Back ROM slot (included below).
• Up to 4 MB of RAM. Main memory moved from the FPGA's own block RAM into
  the MEGA65's 64 MB SDRAM chip, which is what makes the 4096k tier — the
  largest the original MiSTer core offers — possible at all. RAM options are
  now 128k / 640k / 1024k / 4096k.
• Much more headroom inside the FPGA. Moving main RAM out freed about 160
  block RAM tiles: the design went from 70% of the chip's block RAM to 26%, and
  its worst-case timing margin roughly quintupled. Not a user-visible feature,
  but it is where future features will be built.

⚠️ Board support

This release is for the MEGA65 R6.

• R3 owners: stay on V1.01.
  The R3 has no SDRAM chip, so V1.5 cannot run on it. V1.01 remains available
  and supported, and includes a HyperRAM timing fix made specifically for the
  R3 — it is the best build this core has ever had for that board.
• R4 / R5 owners: your board has the same SDRAM chip as the R6, but each
  revision needs its own core build and nobody has tested one yet. Only an R6
  .cor is published here. If you have one and would like to try, open an
  issue.

Hard disk: where to get an image, and keep it small

Marcel Kilgus's QL-SD page, https://www.kilgus.net/ql/ql-sd/, has
qxl_empty.zip — empty, ready-to-use QXL.WIN files in several sizes. That is
the easiest way to start. The same page also has qlsd_win_demo.zip, an
example image with utilities, a boot file and some ready-to-run QL games, plus
the QL-SD documentation.

Mounting copies the whole image into memory at roughly 6-7 seconds per
megabyte, so 4 to 8 MB is a comfortable size — an 8 MB image costs about
a minute every time you mount it. The core enforces a 32 MB ceiling. A future
version will stream sectors straight from the SD card and remove both the wait
and the limit.

Toolkit II and the QL-SD driver both occupy the Back ROM slot, so you can have
one or the other, not both.

Files

File	What it is
QL4M65-CoreQL-V1.5_r6.cor	The core, for MEGA65 R6
main.rom	Minerva 1.98a1 system ROM
back.rom	Toolkit II
qlsd_driver_back.rom	QL-SD driver 1.09 — needed for the hard disk
blank.mdv	A blank, correctly-formatted microdrive image
INSTRUCTIONS.md	Full installation and usage instructions — read this first

Credits

Minerva is by Laurence Reeves and Toolkit II by Tony Tebby / QJUMP,
both freely redistributable.

The QL-SD driver 1.09 is by Wolfgang Lenerz and Marcel Kilgus ("WL + MK
2020") — all credit for it is theirs. It came from MiSTer_QL_OS_qlsd109.zip
published at https://www.kilgus.net/ql/ql-sd/, which is also where to go for
the original file, the QL-SD hardware documentation and any newer version. It
is included here for convenience only, with attribution and no claim of
ownership; if the authors would rather it were not redistributed, it will be
removed immediately — please just say so.

The SDRAM controller that makes this release possible is by Michael
Jørgensen (https://github.com/MJoergen/SDRAM), heading for M2M V2.1.0.
Marcel Kilgus also maintains QL_MiSTer,
the core this is ported from, and sy2002 and MJoergen are the authors of
MiSTer2MEGA65 itself.

Other QL ROMs (JS, MGE, AH…) are commercial software still under copyright and
are not distributed here — see the
Sinclair QL ROM archive.