open-roms/CONFIG.md

Configuring the build

It's not possible to provide ROM builds that suit everyone needs - therefore configuration files were introduced, few predefined configurations are provided with sane defaults:

• src/,,config_custom.s
• src/,,config_generic.s
• src/,,config_mega65.s
• src/,,config_ultimate64.s
• src/,,config_testing.s

Just edit them and recompile the project. To enable particular option - uncomment it by removing leading // from before #define directive (as you probably guessed, commenting out disables it). Some options are followed by constants - you can change them too to further fine-tune the build.

Note however, that features do not came for free - enabling them needs some additional ROM space (in BASIC segment, in KERNAL segment, or in both), which is VERY limited on the target machines. Some options might be unavailable for speecific targets - read the comments in the configuration files. Some options might also carry compatibility and/or performance hit - so choose wisely.

Hardware platform

CONFIG_PLATFORM_COMMODORE_64

Commodore 64 is the only hardware platform available now - and the main one, as the Open ROMs API is meant to be compatible with the Commodore 64.

Since Open ROMs is highly modular, it should be possible to add other platforms in the future (like 8-bit Atari computers or Commander X16), if they share the following common characteristics:

• MOS 6502 CPU or compatible
• 8KB ROM area $A000-$BFFF
• 8KB ROM area $E000-$FFFF

CONFIG_MB_M65, CONFIG_MB_U64

Select if the ROM is going to be used exclusively on the specified motherboard. It prevents from enabling options not having sense, skips initialization of C128-only registers, and enables motherboard-specific features.

Brand

Branding is only allowed for C64 platform, if no motherboard is specified.

CONFIG_BRAND_CUSTOM

Intended for custom builds, for private purposes. Allows to configure branding with CONFIG_CUSTOM_BRAND macro.

CONFIG_BRAND_GENERIC

If you don't know which variant to choose - select this one.

CONFIG_BRAND_TESTING

Use this one for any kind of testing/experimental build.

Processor instruction set

Processor type should be set only for C64 platform, if no motherboard is specified. Otherwise, it will be selected automatically. Setting proper CPU allows to enable various size/performance optimizations.

CONFIG_CPU_MOS_6502

Choose if your CPU only supports the original MOS Technology 6502 instruction set, like:

• MOS 6510 - used in the Commodore 64
• MOS 8500 - used in the Commodore 64C
• MOS 8502 - used in the Commodore 128

If unsure - select this one.

CONFIG_CPU_DTV_6502

Choose if your CPU only supports extended C64 DTV instruction set.

CONFIG_CPU_RCW_65C02

Choose if your CPU supports the Rockwell 65C02 instruction set.

CONFIG_CPU_WDC_65C02

Choose if your CPU supports the Western Design Center 65C02 instruction set, like:

• WDC 65C02 - used in the Turbo Master accelerator

CONFIG_CPU_WDC_65816

Choose if your CPU supports the 16-bit Western Design Center 65816 instruction set, like:

• WDC 65C816 - used in the Flash 8 accelerator
• WDC 65C816S - used in the SuperCPU accelerator

CONFIG_CPU_CSG_65CE02

Choose if your CPU supports the Commodore Semiconductor Group 65CE02 instruction set, like:

• CSG 65CE02
• CSG 4510 - microcontroller used in the Commodore 65 prototypes

Memory model

Different layouts of memory are possible - but they can be selected at compile time only.

CONFIG_MEMORY_MODEL_38K

Memory model the original machine uses - memory available for BASIC ends at $9FFF, just before the first block of ROM. The fastest and the most compatible, but gives the least memory for BASIC. If unsure - select this one.

CONFIG_MEMORY_MODEL_46K and CONFIG_MEMORY_MODEL_50K

These models additionaly use RAM under BASIC, and the 50K additionally takes over $C000-$CFFF range. They should still be highly compatible (no additional RAM for helper routines is needed), and the performance penalty should be much lower than 60K model.

CONFIG_MEMORY_MODEL_60K

Uses RAM under BASIC, I/O and KERNAL, takes over $C000-$CFFF area requires special helper routines installed in $2A7-$2FF area (normally unused and free for the user). Gives the most free memory for BASIC programs, but it's the slowest (for example, forces disabling optimized LOAD loop for JiffyDOS) and the least compatible model.

It is currently not compatible with MEGA65 extended ROMs.

Comparing to standard memory model, it needs about 180 bytes in BASIC segment and 80 bytes in KERNAL segment - at the moment of doing the test, these values are expected to change often.

IEC bus

IEC bus, also known as Serial Port, is a standard interface to connect disk drives, printers, SD2IEC device, etc.

CONFIG_IEC

Adds support for the IEEC bus - for serial printers, disk drives, etc.

Needs over 1000 bytes in KERNAL segment. If unsure - enable.

CONFIG_IEC_DOLPHINDOS

Adds support for DolphinDOS fast protocol to the IEC bus, using UserPort cable.

Needs about 160 bytes in KERNAL segment. If unsure - enable.

CONFIG_IEC_DOLPHINDOS_FAST

Faster LOAD loop implementation for DolphinDOS protocol.

Needs 20 more bytes in KERNAL segment.

CONFIG_IEC_JIFFYDOS

Adds support for JiffyDOS fast protocol to the IEC bus.

Needs about 430 bytes in KERNAL segment. If unsure - enable.

CONFIG_IEC_JIFFYDOS_BLANK

Causes screen blanking during JiffyDOS file loading to increase performance.

Tape deck

Note: for MEGA65 most of the tape support code is placed in it's extended ROM; very little of the (tiny) KERNAL segment is used.

CONFIG_TAPE_NORMAL

Adds a minimal normal (standard Commodore format) tape support - just LOAD command.

Needs about 1050 bytes in KERNAL segment (if both normal and turbo are enabled, about 900 bytes are needed, as they share some code). If unsure - enable.

CONFIG_TAPE_TURBO

Adds a minimal turbo tape support - just LOAD command (device 7, like on Action Replay and Final cartridges), up to 250 blocks

Needs about 700 bytes in KERNAL segment (if both normal and turbo are enabled, about 1300 bytes are needed, as they share some code). If unsure - enable.

CONFIG_TAPE_AUTODETECT

Tape format (normal/turbo) is always autodetected.

Needs about 100 more bytes in KERNAL segment.

CONFIG_TAPE_NO_KEY_SENSE

Enable this option if you are using a tape interface adapter with some audio signal source connected. These adapters lack key sense functionality, so the computer is unable to tell whether Play got pressed or not - this option changes the ROM behaviour, so that it can detect Play pressed when impulses start arriving from the tape.

CONFIG_TAPE_NO_MOTOR_CONTROL

Enable this option if you are using a tape interface adapter lacking tape motor control (most likely every adapter currently being sold) - this will eliminate the need to quickly press space when the program header information gets displayed. Note: if you are using a cassette player with REM port, and your adapter is connected to this port too, than you do not need this option.

Sound support

The original Commodore 64 had one SID sound chip installed. However, mods exists to add more of them for improved sound capabilities. Emulators and FPGA machines typically allow to simulate more than one too. Unfortunately, there is no standard regarding how these additional chips are visible in the processor address space, and there is no sane way to detect it - thus, it has to be configurable.

The SID support in the ROM is very limited - it only disables the sound during startup or warm restart (when STOP+RESTORE is pressed or BRK assembler instruction is executed).

CONFIG_SID_2ND_ADDRESS and CONFIG_SID_3RD_ADDRESS

Each of them add support for one additional SID - addresses should be given as parameter, respectively. Do not use when CONFIG_MB_M65 is selected - the motherboard support code already knows the SID locations.

Each of these options needs 3 bytes in KERNAL segment.

CONFIG_SID_D4XX and CONFIG_SID_D5XX

Cause the system to support SIDs in $D4xx and $D5xx ranges, respectively.

Each of them needs a couple of bytes in KERNAL segment - but they can share some code, and $D4xx range support replaces the standard $D400 address handling, so exact amount depends on the exact configuration. Do not use when CONFIG_MB_M65 is selected - the motherboard support code already knows the SID locations.

Keyboard

Original keyboard support routine is just horrible. It does nothing to prevent ghosting - press A+S+D at the same time - it prints F. Try to use joystick connected to control port 1 - it outputs phantom characters. The Open ROMs provides much more sophisticated routines to prevent such problems.

CONFIG_LEGACY_SCNKEY

Uses old Open ROMs keyboard scanning routine, which is basically the example routine by TWW/CTR, hacked to work within Kernal. It's greatest advantage is multi-key rollover, it's disadvantages - it's much less compatible (uses several bytes of memory which are normally free for user software - thus, it is considered legacy for now), does not support all the system variables (RPTFLG and KEYLOG are unsupported), and ignores the configuration options - this can be changed, but it requires some effort.

Needs 30-250 more space in KERNAL segment (depending on the features enabled for current default routine). If unsure - disable.

CONFIG_KEYBOARD_C128

Allows to use additional keys found on the C128 keyboard.

Needs about 130 bytes more space in KERNAL segment. If unsure - disable.

CONFIG_KEYBOARD_C128_CAPS_LOCK

Allows to use CAPS LOCK key on the C128 keyboard, this is independent from CONFIG_KEYBOARD_C128. Support is C64-safe (there is a protection against false-positive reading on the C64).

Needs about 50 bytes more space in KERNAL segment. If unsure - disable.

CONFIG_KEYBOARD_C65, CONFIG_KEYBOARD_C65_CAPS_LOCK

Similar, but for C65 keyboard. Please note - the C65 keyboard support is (as of yet) completely untested!

CONFIG_KEY_REPEAT_DEFAULT

Enables key repetition by default during the startup (sets RPTFLG).

Needs 5 bytes more space in KERNAL segment.

CONFIG_KEY_REPEAT_ALWAYS

Enables the key repetition and ignores RPTFLG.

Saves 22 bytes from KERNAL segment.

CONFIG_KEY_FAST_SCAN

Performs somee speed optimizations in the keyboard scanning routine, at the expense of some more ROM space.

Needs 13 bytes more space in KERNAL segment. Only disable if you are running out of ROM space.

CONFIG_JOY1_CURSOR and CONFIG_JOY2_CURSOR

Joystick movement also moves the cursor.

Needs about 65 bytes of ROM space in KERNAL segment to handle both joysticks.

CONFIG_PROGRAMMABLE_KEYS

Allows to assign commands to any function key, RUN key and HELP key (if selected keybaord has one) - just fill-in appropriate CONFIG_KEYCMD_* variable(s). Keys not present on the selected keyboard are ignored.

Needs 25 bytes more space in KERNAL segment for the code. In addition, each configured key takes 3 bytes + length of the command.

Screen editor

CONFIG_EDIT_STOPQUOTE

If enabled, STOP key terminates insert/quote mode (like on some Black Box cartridges).

Feature needs 12 bytes in KERNAL segment. If unsure - enable.

CONFIG_EDIT_TABULATORS

If enabled, allows use of TAB (or CTRL+>) and SHIFT+TAB (or CTRL+<) to switch between predefined tabulator positions.

Feature needs 35-45 bytes in KERNAL segment. If unsure - enable.

Software features

CONFIG_PANIC_SCREEN

If enabled, certain fatal errors will produce a nice bluescreen instead of just resetting the machine.

Feature needs over 100 bytes in KERNAL segment. If unsure - enable.

CONFIG_DOS_WEDGE

If enabled, a simple DOS wedge is available from the direct mode - supports @<drive_number>, @<command>, @$, @$<params> and @ commands.

Feature needs about 330 bytes in BASIC segment. If unsure - enable.

CONFIG_TAPE_WEDGE

If enabled, a simple DOS wedge is available from the direct mode for tape loading - supports ←L (for LOAD) and ←M (for MERGE), optionally with a file name.

Feature needs several bytes in BASIC segment. If unsure - enable.

CONFIG_TAPE_HEAD_ALIGN

If enabled, embeds a tape head align tool into the ROM, it can be started with ←H. Requires CONFIG_TAPE_WEDGE.

Feature needs about 800 bytes in KERNAL segment. Only recomended for machines with extended ROM, like MEGA65.

CONFIG_BCD_SAFE_INTERRUPTS

On the most widespread CPUs the D flag is not cleared upon entering interrupts. Since the original Kernal does not clear it either, it's not safe to use BCD processor mode without disabling the interrupts first. This option makes sure the D flag is disabled at the start of the interrupt - this allows some optimizations in the code.

Feature needs 2 bytes in KERNAL segmment (for CPUs needing the patch), but at the same time allows optimizations allowing to gain some more bytes. If unsure - enable.

Eye candy

CONFIG_COLORS_BRAND

Tries to adjust the color scheme to the selected brand. Some brands might not support this.

CONFIG_BANNER_SIMPLE, CONFIG_BANNER_FANCY

Select startup banner - either a simple one, or with some colorful elements.

Richer banners need more BASIC segment, varies between brands.

CONFIG_SHOW_FEATURES

If enabled, shows the most important compiled-in features on the startup screen. Also shows the video system (PAL/NTSC).

It is recommended to keep it enabled for informational purposes.

Debug options

Options in this section are for debug purposes only. If unsure - disable.

CONFIG_DBG_STUBS_BRK

Replaces RTS stubbed routines implementation with one causing a break.

CONFIG_DBG_PRINTF

Makes printf routine available.

Other options

CONFIG_COMPRESSION_LVL_2

Adds additional step in compressing BASIC interpreter strings - a dictionary compression. Not tested extensively - and for now it won't bring any improvement (it will even increase the code/data size) as we do not have enough strings yet to make this method useful. Do not use!