C128 (unofficial) for MiSTer

In development, not complete

Based on C64_MiSTer by sorgelig.

Based on FPGA64 by Peter Wendrich with heavy later modifications by different people.

C128 features implemented

• MMU fully implemented and tested using VICE test progs
• C128 specific keys
• VIC jailbars for the authentic C128 video experience
• VDC standard modes (text & bitmap) implemented
• Selectable colour palettes for the VDC
• Booting in C64, C128 or CP/M mode
• Automatic detection of .CRT files: C64 cartridges boot in C64 mode, C128 cartridges boot in C128 mode. C128 .CRT files must contain a C128 CARTRIDGE header to be detected.
• Loading of .PRG files to the correct memory location in C128 mode.
• Fast serial (external) IEC
• 1570/1571 drive, .d71/.g71 images, including MFM format

Implemented but untested

The following features should work but have not been tested. If you have an opportunity to test this, please let me know the result by creating an issue on GitHub (for both success and failures)

• Parallel disk I/O on the 1571 (Dolphin DOS)

C128 features not (yet/fully) implemented

• VDC scrolling, interlace, 40 column mode, non-standard modes
• Internal function ROM
• 1571DCR drive model option for the full 128DCR experience. This model uses a custom MFM en/decoding chip which seems to be completely undocumented.

Extras being worked on

• • 16mb RAM banked into banks 2 and 3 (mostly implemented)
• • MMU has been overhauled, will register as "version 2" with "up to 256 RAM banks".
• • Currently wraps at 8mb, (128 RAM banks) some of the core seems to be at page 147 and above and accessing it crashes the machine.
• • • Probably stuff in SDRAM needs to be reorganized.
• • Think, VIC page flipping with hundreds of pages available.
• • Implementation:
• • • Check for 16mb MMU ($d50b = $x2)
• • • Check how many pages have been provided ($x2) where x = 2^x pages available.
• • Select one of available RAM banks (even 0 and 1) by placing a byte in $d50c for bank 2 and $d50d in bank 3.
• • See the "C128MMUv2.txt" for more details.
• • 85816 CPU (65816 with 6510/8502 glue) (partial implementation, issues)
• • CPU MUX between t65 and SNES 65816 core built. It can even kind of boot (but BASIC freaks out and there are timing issues) yet Run/stop Restore still responsive.
• • 16mb RAM that can be banked in on MMUv2 will be directly accessible to the 65816.
• • CPU_6510 now makes assumptions that there is 16mb of RAM and it can only see 64k of it.
• • I/O registers only visible at 000000-000001
• • Note this may end up being the 85832 (32 bit 65xx compatible) so stay tuned.
• VDC RAM exposed to CPU (soon)
• • This will allow people to draw directly to the VDC RAM.
• • I don't know where it is currently mapped. If Eric puts it somewhere in 040000-FEFFFF, then it will be able to be banked into bank 2 or 3 :)
• • I will recommend its position be at $F00000 (banks 240-254) because I have plans for big VDC enhancements.
• • Page 255 should be reserved for the 85816.
• VDC registers exposed at $D680 (soon)
• • Accessing the entire VDC through 2 registers ($d600/$d601) was a mistake by Commodore. Lets fix that.
• Enhanced VDC modes
• • 256 color mode (CLUT)
• • 640x400 progressive mode
• • Maybe more ...
• SD2IEC simulation
• • Likely. I feel like we should have some kind of mass storage solution lol
• Sound .. is pretty already covered with 2 SIDs, and OPL2, and a Digimax.
• • If there is room, might expand to 4 SIDs
• SuperCPU 128 registers (later)
• • Not all will be implemented because not all make sense on MiSTer, but the SuperCPU will be faked enough to allow applications targetting it to run.
• 20mhz mode? (maybe)
• • I hope. Theres some barriers. Depends on how fast a base clock we can have...
• Backporting 85816/85832 to C64
• • When it is stable, definitely.
• • Backporting these other features, probably not, because the C128 does have a C64 mode. And the C64 mode has access to much of this...
• MMU exposed in C64 mode
• • Is there a point?
• Z80 SMP (Way later)
• • Is it possible? Writing point here to explore it...

• = In progress

• = Complete

Other TODOs and known issues

• Automatic detection of C64/C128 .PRG files to boot in the appropriate mode.
• Re-enable 3x and 4x turbo modes for 8502
• Turbo mode for Z80

Usage

Internal memory

In the OSD->Hardware menu, internal memory size can be selected as 128K or 256K. The latter activates RAM in banks 2 and 3. C128 basic does not detect this memory however, so it will still show 122365 bytes free.

ROM set

The ROM set option in the OSD->Hardware menu lets you switch between standard C128 and C128DCR roms.

Char switch

The Char switch option in the OSD->Hardware menu lets you select how the two character ROM banks are switched.

English versions of the C128 switch character set depending on C128 or C64 mode, whereas international versions of the C128 have an "ASCII/DIN" key that replaces the "CAPS LOCK" key to manually switch character sets. Since the C128 keys are not implemented yet, setting this to "CAPS LOCK" locks the character set to C128 mode.

Loadable ROM

External ROMs can be loaded to replace the standard ROMs in OSD->Hardware.

ROM 1/4: Expects a 16kB, 32kB or 40kb file. First 16 kB contains C64 basic and kernal (a.k.a ROM1), next 16 kB contains the C128 kernal (a.k.a ROM4), and the last 8 kB is loaded as the character rom. This makes it possible to load international versions of the C128 OS as a single file.

It's possible to only change the C64 ROM by loading a 16 kB ROM image, or the contents of both ROM1 and 4 without updating the character rom by loading a 32 kB image.

Note: some C64 ROM files created for the C64 MiSTer core are bigger than 16kB and include the disk ROM as well, for example the Dolphin DOS ROM. These ROM files will not work with this core as they will overwrite the C128 kernal parts. To use these ROMs the C64 and drive ROM parts must be loaded separately.

ROM 2/3: Expects a 32kB file containing the complete C128 basic ROM. C128 kernal and C128 basic ROM versions must match to function correctly.

Function rom: Loads the internal function ROM. Not implemented yet.

Drive rom: Loads the ROM for the disk drive. The file extension determines to which drive model the ROM image is applied to:

• .R41: ROM for the 1541 drive
• .R70: ROM for the 1570 drive
• .R71: ROM for the 1571 drive
• .R81: ROM for the 1581 drive

For example, to load a Dolphin DOS ROM for the 1541, the filename must end with .R41, e.g. DOLPHIN.R41

VDC/80 column mode

Video output can be selected using the keyboard. Pressing * or AltGr+F7 emulates the 40/80 display toggle switch on the C128 keyboard. This will also switch which video output is shown on the VGA/HDMI output of the MiSTer.

In OSD->Audio&Video the VDC version, memory size and colour palette can be selected.

There are four colour palettes selectable for the VDC:

• Default: the "standard" TTL RGBI colour palette
• Analogue: the palette when using resistors to convert TTL RGBI to analogue RGB
• Monochrome: TTL monochrome monitor, with two levels of intensity
• Composite: the black and white image on the composite pin of the DB9 TTL RGBI connector, no intensity

Keyboard

• F2, F4 , F6 , F8 , Left/Up keys automatically activate Shift key.
• F9 - arrow-up key.
• F10 - = key.
• F11 - restore key. Also special key in AR/FC carts.
• Meta keys (Win/Apple) - C= key.
• PgUp - Tape play/pause
• PgDn - Line feed
• End - Help
• Pause/Break - No Scroll (* see note below)
• Numpad / - Esc
• Numpad * - Display 40/80

The AltGr key (right Alt) is used to access alternative function keys. Combined with AltGr the function keys are the C128 top-row special keys. To access these functions, press and hold AltGr while pressing any of the function keys:

• AltGr+F1 - Esc
• AltGr+F2 - Alt
• AltGr+F3 - Tab
• AltGr+F4 - Caps Lock
• AltGr+F5 - Help
• AltGr+F6 - Line feed
• AltGr+F7 - 40/80 display
• AltGr+F8 - No scroll

It is possible to access the C128 top-row cursor keys, and the numpad keys on a PC keyboard without numpad using AltGr combined with the similar keys:

• AltGr+return - Numpad enter
• AltGr+1 through 0 - Numpad 1 through 0
• AltGr+- - Numpad -
• AltGr++ - Numpad +
• AltGr+. - Numpad .
• AltGr+Cursor keys - Top-row cursor keys (** see note below)

Shift lock can be activated by pressing AltGr+Shift. This is a toggle, to release Shift lock, press the AltGr+Shift combination again.

Keys marked in blue are the keys sent when combined with AltGr.

*): The Pause/Break key acts like the No scroll key, however the Pause/Break PC key is special as it does not send a signal when it is released. To solve this, when the Pause/Break key is pressed, the No scroll key signal to the C128 is pulsed for short period. To hold No scroll on the C128 for longer, either use AltGr+F8, or quickly double press Pause/break and press any key to release No scroll.

**): When the Z80 CPU is active the top-row cursor keys become the default and AltGr selects the regular cursor keys.

C128 cartridges

To load a cartridge - "External function ROM" in C128 terms - it must be in .CRT format. To convert a binary ROM image into a .CRT, the cartconv tool from Vice can be used, usually like this:

cartconv.exe -t c128 -l 0x8000 -i cart.bin -o cart.crt

The -t c128 option is needed to create the correct header indicating this is a C128 cartridge. Otherwise the cartridge will be detected as a C64 cartridge and the core will start up in C64 mode like a real C128 would do if a C64 cartridge is inserted.

The -l 0x8000 option is needed to indicate the image should be located at address $8000. Some external ROMs might need to be located at $C000, in that case -l 0xC000 should be used.

USER_IO pins

USER_IO	USB 3.0 name	Signal name
0	D+	RS232 RX
1	D-	RS232 TX
2	TX-	IEC /CLK
3	GND_d	IEC /RESET
4	RX+	IEC /DATA
5	RX-	IEC /ATN
6 🆕	TX+	IEC /SRQ

All signals are 3.3V LVTTL and must be properly converted to required levels!

The IEC /SRQ (USER_IO6) line is required for IEC fast serial operation with an external 157x or 1581 drive. You will need a MiSTer user port adapter that connects the /SRQ line. Assume a MiSTer user port to IEC adapter does not connect this line unless it is explicitly stated that it supports the C128 fast serial protocol.

C64 features

The following is the original C64_MiSTer README. Some features still apply, others don't:

Features

• C64 and C64GS modes.
• C1541 read/write/format support in raw GCR mode (*.D64, *.G64)
• C1581 read/write support (*.D81)
• Parallel C1541 port for faster (~20x) loading time using DolphinDOS.
• External IEC through USER_IO port.
• Amost all cartridge formats (*.CRT)
• Direct file injection (*.PRG)
• Dual SID with several degree of mixing 6581/8580 from stereo to mono.
• Similar to 6581 and 8580 SID filters.
• REU 16MB and GeoRAM 4MB memory expanders.
• OPL2 sound expander.
• Pause option when OSD is opened.
• 4 joysticks mode.
• RS232 with VIC-1011 and UP9600 modes either internal or through USER_IO.
• Loadable Kernal/C1541 ROMs.
• Special reduced border mode for 16:9 display.
• C128/Smart Turbo mode up to 4x.
• Real-time clock

Installation

Copy the *.rbf to the root of the SD card. Copy disks/carts to C64 folder.

Usage

Using without keyboard

If your joystick/gamepad has more than 4 buttons then you can have some limited usage of keyboard. Joystick buttons Mod1 and Mod2 adds 12 frequently used keys to skip the intros and start the game. Considering default button maps RLDU,Fire1,Fire2,Fire3,Paddle Btn, following keys are possible to enter:

• With holding Mod1: Cursor RLDU, Enter, Space, Esc, Alt+ESC(LOAD"*" then RUN)
• With holding Mod2: 1,2,3,4,5,0,Y,N
• With holding Mod1+Mod2: F1,F2,F3,F4,F5,F6,F7,F8

With maps above and using Dolphin DOS you can issue F7 to list the files on disk, then move cursor to required file, then issue Alt+ESC to load it and run.

Loadable ROM

(not applicable to C128_MiSTer)

Alternative ROM can loaded from OSD: Hardware->Load System ROM. Format is simple concatenation of BASIC + Kernal.rom + C1541.rom

To create the ROM in DOS or Windows, gather your files in one place and use the following command from the DOS prompt. The easiest place to acquire the ROM files is from the VICE distribution. BASIC and KERNAL are in the C64 directory, and dos1541 is in the Drives directory.

COPY BASIC + KERNAL + dos1541 MYOWN.ROM /B

To use JiffyDOS or another alternative kernel, replace the filenames with the name of your ROM or BIN file. (Note, you muse use the 1541-II ROM. The ROM for the original 1541 only covers half the drive ROM and does not work with emulators.)

COPY /B BASIC.bin +JiffyDOS_C64.bin +JiffyDOS_1541-II.bin MYOWN.ROM

To confirm you have the correct image, the BOOT.ROM created must be exactly 32768 or 49152(in case of 32KB C1541 ROM) bytes long.

There are 2 loadable ROM sets are provided: DolphinDOS v2.0 and SpeedDOS v2.7. Both ROMs support parallel Disk Port. DolphinDOS is fastest one.

For C1581 you can use separate ROM with size up to 32768 bytes.

Autoload the cartridge

In OSD->Hardware page you can choose Boot Cartridge, so everytime core loaded, this cartridge will be loaded too.

Parallel port for disks.

Are you tired from long loading times and fast loaders aren't really fast when comparing to other systems?

Here is the solution: In OSD->System page choose Expansion: Fast Disks. Then load DolphinDOS_2.0.rom. You will get about 20x times faster loading from disks!

Turbo modes

(not applicable to C128_MiSTer, C128 mode is always active)

C128 mode: this is C128 compatible turbo mode available in C64 mode on Commodore 128 and can be controlled from software, so games written with this turbo mode support will take advantage of this.

Smart mode: In this mode any access to disk will disable turbo mode for short time enough to finish disk operations, thus you will have turbo mode without loosing disk operations.

RS232

Primary function of RS232 is emulated dial-up connection to old-fashioned BBS. CCGMS Ultimate is recommended (Don't use CCGMS 2021 - it's buggy version). It supports both standard 2400 VIC-1011 and more advanced UP9600 modes.

Note: DolphinDOS and SpeedDOS kernals have no RS232 routines so most RS232 software don't work with these kernals!

GeoRAM

(untested in C128_MiSTer, probably only works in C64 mode)

Supported up to 4MB of memory. GeoRAM is connected if no other cart is loaded. It's automatically disabled when cart is loaded, then enabled when cart unloaded.

REU

Supported standard 512KB, expanded 2MB with wrapping inside 512KB blocks (for compatibility) and linear 16MB size with full 16MB counter wrap. Support for REU files.

GeoRAM and REU don't conflict each other and can be both enabled.

Real-time clock

RTC is PCF8583 connected to tape port. To get real time in GEOS, copy CP-CLOCK64-1.3 from supplied disk to GEOS system disk.

Raw GCR mode

C1541 implementation works in raw GCR mode (D64 format is converted to GCR and then back when saved), so some non-standard tracks are supported if G64 file format is used. Support formatting and some copiers using raw track copy. Speed zones aren't supported (yet), but system follows the speed setting, so variable speed within a track should work. Protected disk in most cases won't work yet and still require further tuning of access times to comply with different protections.