The C64 KERNAL uses a vector table at page 3 to allow redirection of common KERNAL file handling and basic functions. This feature is used by IDEDOS to hook into the C64 KERNAL.
The operating system itself is divided into four pages of 16 KiB which are mapped in when required. The mapping is temporarily switched off while interrupts are running for increased compatibility, however this causes a ≈40 μs latency.
Additional RAM for buffers and internal data are also mapped in from either the IDE64 cartridge (28 KiB) or the additional RAM of the SuperCPU is used. The standard KERNAL memory locations at page zero and page two are handled in a KERNAL-compatible way; temporarily used memory is restored after the routines are finished.
Beyond the KERNAL table IDEDOS has two new calls for bulk data handling (read/write) which allows much faster data transfer rates than the character-based I/O.
The native file system is non-CBM style at the low level to allow partitions greater than 16 MiB. High-level features like the 16-character filenames or filetypes are retained. Due to complexity and memory requirements, the filesystem creation and consistency check is not part of the operating system, unlike CBM DOS or CMD DOS.
Additional filesystems like ISO 9660 or FAT are abstracted internally and mostly use the same routines for handling, thereby little difference is noticeable to user programs, except if some features are not fully implemented.
The device handling is done by additional device numbers assigned to the new devices. The device numbers for IDEDOS devices are configurable and is normally in the range of 10–14. Over the years many programs assumed that there is only device 8 and do not allow selecting anything else; this can be worked around by temporary changing the used IDEDOS device number to 8.
For standard devices, the original KERNAL routines are used, while IDEDOS devices use custom routines which closely imitate the results and behavior of KERNAL calls for floppy devices. KERNAL calls not going through the vector table (most notably IEC bus-specific calls) present an incompatibility with those programs using them.
Special features (like CD-ROM audio handling) are implemented by new channel 15 commands, while features not found on floppy drives follow the CMD style commands to allow programs to easily support a wider range of devices.
Unlike intelligent external devices which have a separate processor (like 1541 with CBM DOS), IDEDOS runs on the host computer, thereby all disk routines block until finished. This rules out the use of "IRQ loaders" which are commonly used to speed up operation of serial bus peripherals.
Interrupts are generally allowed while IDEDOS is running (they are disabled on rare time-critical operations), however the system was written to be non-reentrant, just like the original KERNAL.
Short history
In 1996 IDEDOS was born, as there was a need for a system to run the IDE64 1.1 card. It was created by Josef Souček (main code) and Tomáš Přibyl (File manager, Final cartridge monitor adaptation). Additional code came by Jan Vorlíček (BASIC extension), Jan Hlaváček (Duart PCLink).
In 2000 Kajtár Zsolt added CD-ROM support, new setup code and lot of fixes. Due to limitations of the design the development of a completely rewritten version (0.90) was started by Kajtár Zsolt, which was not ready for general use before 2005. Meanwhile, the old version reached 0.898b in June 2004.
In 2009 the 64 KiB limit for the system started to get tight, and the IDEDOS 0.91 beta was started to refactor the code to gain more space and internal flexibility.
IDEDOS 0.898b
This was the last version of the old IDEDOS series.
Device support
2 ATA(PI) devices: hard disk, CompactFlash, CD-ROM, DVD
Fast load can be switched off in setup in case of incompatibility (non-1541 as device 8). Minimum interleave is 7, fast saver is only supported in manager, and uses an interleave of 8. PAL/NTSC compatible timing.
Includes clock with calendar, ability to set drive numbers, screen colours, auto boot, floppy fast loader, basic clock (TI$), power management, write retry, read-ahead and write cache drive settings, CD-ROM slow down option.
BASIC extensions
The BASIC extension includes disk handling commands (limited to IDEDOS devices), and adds some new error messages. Commands:
It can be used to navigate around directories, start programs, copy/rename/delete files, create directories, and execute plugins to operate on files. Recursive file copy was only added in 0.898b, and in rare cases it does not work.
Monitor
The monitor is almost exactly the Final cartridge monitor in IDEDOS 0.89. Only standard 6502 opcodes are available. The commands are:
The file managers inspiration comes from 0.89, though it was rewritten from scratch. The goal was to have a file manager which not only supports IDEDOS devices, but also works well with CMD and other drives.
Monitor
The monitor was rewritten from scratch, the main inspiration was the CCS64 emulator's monitor, but some command ideas came from FC3/AR7/Vice monitors. The goal was to have freezer style (all registers including I/O editable) and fast machine code monitor which supports illegal 6502 and SuperCPU emulation mode opcodes.
Commands:
@ – Disk command, status and directory
A – Assemble
B – Memory configuration, select RAM/ROM
BT – Backtrace
C – Compare memory
D – Disassemble
, – Write hex data to memory and disassemble
EC – Edit char (binary)
[ – Write binary data to memory
ES – Edit sprite (binary)
] – Write binary sprite data to memory
F – Fill memory with byte
G – Execute at address
H – Search hex/any/text
I – Dump memory in PETSCII
' – Write PETSCII data to memory
IO – Dump I/O registers
- – Write hex data to I/O memory
IV – Restore I/O vectors
J – Dump memory in screen code
. – Write screen code data to memory
K – Defreeze memory
L – Load program
LB – Load binary
M – Dump memory in hex and PETSCII
: – Write hex or PETSCII data to memory
N – Number conversion and calculator
O – Select work drive
R – Show registers
; – Change registers
S – Freeze memory/save program
SB – Save binary
T – Copy memory
V – Verify program
VB – Verify binary
X – Continue program
Q – Exit to BASIC warm start
←/↑ – Push and pop address(es) to stack.
Miscellaneous features
Auto boot - can load and start a file on reset or power on.
Custom screen, monitor and manager colours - the default colours can be changed.
Set the TI$ BASIC variable to the correct time on reset.
Displays the start and end address for load/save.
Special extension for bulk reading and writing of file data
