JiffyDOS Kernal Upgrade

JiffyDOS Kernal Upgrade

Caption	JiffyDOS 64 Kernal v6.01 on a RETRO Innovations ROM-el adapter, fitted in the Kernal ROM socket of a Commodore 64 board
Type	Kernal and drive DOS ROM replacement
Designer	Mark Fellows
Manufacturer	Mark Fellows; marketed by Creative Micro Designs; now sold under licence by RETRO Innovations and others
First released	Unknown
Latest revision	Still sold under licence
Operating voltage	—
Layers / PCB	—
Compatibility	C-64, 64C, SX-64, C-128, C-128D; 1541, 1541C, 1541-II, 1571, 1581 and sixteen third-party drives
Features	Faster serial transfers, DOS Wedge commands, extra disk commands, function-key definitions, switch back to stock ROMs
Model No.	Version 6.01 (1989)

JiffyDOS is a replacement Kernal ROM for the Commodore 64, SX-64 and C-128, with matching replacement DOS ROMs for their disk drives. It was written by Mark Fellows and sold by Creative Micro Designs (CMD). It speeds up disk access over the standard serial bus without extra cables, adds the Commodore DOS Wedge commands and several of its own, and is fitted with a switch that returns the computer or drive to its stock ROM. On CMD's figures, loading a 202-block program from a 1541 falls from 124 seconds to 12.

Features

The manual lists these features:

• It uses no ports and no extra cabling: the cartridge, user and cassette ports stay free.
• It includes the Commodore DOS 5.1 Wedge command set, with additions for use inside BASIC programs.
• Extra commands disable the 1541 head rattle, lock and unlock files, list BASIC programs and text files straight from disk, recover a BASIC program after NEW, copy files between drives, change the sector interleave, and print the screen.
• The function keys f1 to f8 are preset to disk commands in BASIC direct mode and work with a directory listing on screen.
• DOS error checking is kept.
• The ROMs carry Commodore's latest fixes. The 1571 ROM fixes bugs affecting relative files and drive initialisation, and the Kernal ROMs are based on Commodore's latest versions.
• PRG, SEQ, REL and USR files are all speeded up. JiffyDOS needs no extra RAM and does not alter vectors, so software that uses the Kernal's disk routines benefits.

RETRO Innovations describes the transfer method as "multi-line serial technology" and says sd2iec-based drives, including its own uIEC, support the JiffyDOS protocol.

Performance

CMD's published figures, in seconds. CMD rounds the times to the nearest second and excludes drive spin-up (about half a second) and directory searching.

Table 1: C-64, SX-64 and C-128 in 64 mode, seconds

Operation	1541 stock	1541 JiffyDOS	1571 stock	1571 JiffyDOS	1581 stock	1581 JiffyDOS
Load 202-block PRG	124	12	124	9	102	8
Save 100-block PRG	75	24	75	20	40	15
Read 125-block SEQ or USR	84	15	84	13	63	9
Write 100-block SEQ or USR	81	27	81	24	44	17
Read 64 × 154-byte REL records	40	14	40	14	37	10
Write one 154-byte REL record	0.350	0.125	0.350	0.120	0.325	0.110
Read/write 16K on the command channel	47	9	47	9	47	9

Table 2: C-128 in 128 mode, seconds

Operation	1541 stock	1541 JiffyDOS	1571 stock	1571 JiffyDOS	1581 stock	1581 JiffyDOS
Load 202-block PRG	124	12	14	9	12	8
Save 100-block PRG	75	24	48	25	26	14
Read 125-block SEQ or USR	84	15	31	12	20	10
Write 100-block SEQ or USR	81	27	48	33	20	11
Read 64 × 154-byte REL records	40	14	21	14	17	10
Autoboot 202-block program	125	13	54	10	13	9
Read/write 16K on the command channel	47	10	10	6	10	6

Loads gain most: about tenfold on a 1541 and more on a 1581 in 64 mode (102 s to 8 s). Saves gain about threefold. The smallest gains are on the 1571 and 1581 in C-128 mode, which are already fast. JiffyDOS writes files with its own sector interleave, so on 1541 and 1571 drives files re-saved under JiffyDOS load faster, in some cases up to three times faster, and remain readable on stock systems. CMD says that for programs that already load quickly on a 1571 in 128 mode, re-saving may be the only way to get a noticeable increase. The interleave can be changed with the @G command on the 1541 and 1571 only; it makes no difference on a 1581.

Supported machines

CMD's 1989 manual lists JiffyDOS for these computers and drives:

Type	Models
Computers	C-64, 64C, SX-64, C-128, C-128D
Commodore drives	1541, 1541C, 1541-II, 1571, 1581
Third-party drives	FSD-1, FSD-2, Excelerator+, Excel 2001, OC-118, MSD-1, MSD-2, Enhancer 2000, BCD/5.25, BCD/128, RF501C, RF512C, FD-168, SW71, Indus GT, CSD-1

The C-128 takes JiffyDOS in both 64 and 128 modes. On the SX-64 there is no separate drive switch. The 1571 and 1581 ROMs need no switch: the drive detects whether the computer is in stock or JiffyDOS mode and selects the matching DOS.

JiffyDOS drives work on stock computers, and JiffyDOS computers work with drives that have no JiffyDOS ROM. CMD sold additional drive ROMs "to speed up second, third or fourth drives".

Hardware

Each JiffyDOS ROM is supplied on an adapter board that plugs into the socket of the ROM it replaces, with a wire to a selector switch.

• C-64 and 64C: CMD's guide shows four board types. All boards except the 64C "V4" board take a 24-pin adapter marked KERNAL; the V4 board takes a 28-pin adapter marked KERNAL-64, and the two are not interchangeable. A Kernal ROM that is soldered in must be removed and replaced with a socket first.
• C-128: two adapters, KERNAL-64 and KERNAL-128, replace the two stock Kernal ROMs.
• 1541: CMD's guide shows four board types (long board, short board, piggyback board and 1541C board). On the piggyback board the DOS ROM is soldered to the piggyback; either solder the JiffyDOS adapter in its place or fit a 1541C adapter in the main socket.
• 1541-II: the drive mechanism is lifted to reach the DOS ROM, and the switch wire must be glued flat to the board so that it cannot touch the drive motor.

RETRO Innovations' licensees sell programmed replacement ROMs, and RETRO Innovations also sells ROM images for owners with their own EPROM programmer.

Installation

The installation guides give these steps for the C-64. The drive and C-128 procedures follow the same pattern.

1. Switch off and unplug the computer and every peripheral, and remove all cables and anything in the cartridge, cassette or user ports.
2. Remove the three case screws, lift the top case, and unplug the keyboard and the power-light cable. On the 64C, also unscrew the keyboard from the lower case.
3. Remove any cardboard, foil or metal shield over the board.
4. Locate the Kernal ROM from the board diagram and lift it out of its socket a little at a time from each end. Keep the stock ROM.
5. Check the JiffyDOS adapter for bent pins and test-fit it with the notch towards the rear of the computer (on the C-128 the notches face the front), then press it fully home.
6. Refit the shield, bending its Kernal contact tab up to clear the taller adapter.
7. Drill a 1/4 inch hole for the selector switch where it cannot foul internal parts, cartridges or cables, and fit the switch.
8. Reassemble, then power up. With the switch in the JiffyDOS position the sign-on screen shows the JiffyDOS banner; in the other position it shows the normal BASIC screen.

If the screen stays blank, switch off at once, recheck the cables, then reseat the adapter. If the problem continues, refit the stock ROM; if the machine then works, the JiffyDOS ROM is faulty. If the switch test fails, operate the switch several times to clear oxidation on its contacts, then check its wiring. On the C-128, refitting the screw near the RF shielding box with the taller adapters fitted can lift the box cover so that it no longer heatsinks the two chips inside, and CMD warns that this can make the machine run erratically; press the cover down firmly.

To check a 1541 after installation, read the error channel (@) straight after power-up. A JiffyDOS drive reports "73, JiffyDOS 5.0 1541, 00, 00" (the version 6 drive ROMs are unchanged from version 5); a stock drive reports "73, CBM DOS V2.6 1541, 00, 00".

Switching ROMs

The normal procedure is to switch the computer or drive off, change the switch, and power up again. CMD designed JiffyDOS to allow switching with the power on, which is useful when a copy-protected program will only load with the stock ROM but runs well with JiffyDOS once loaded. No disk access may be in progress when switching, or the system will hang. Switching the computer's Kernal while a program is running is not completely reliable: the program may crash or hang at its next device access. In BASIC, disable the JiffyDOS commands with @Q before switching to stock, and after switching to JiffyDOS enter SYS 58551 (64 mode) or SYS 65137 (128 mode).

Command reference

A selection from the manual's command descriptions:

Command	Action
@$	Display the directory without overwriting the BASIC program in memory
@	Read the drive error channel (after power-up, shows the DOS type and version)
/name	Load a BASIC program
↑name	Load and run a BASIC program
←name	Save a BASIC program
%name	Load a machine-language program without resetting the BASIC pointers
£name	Load and run a machine-language program
@D:name, @T:name	List a BASIC program or a text file from disk
@O	Recover a BASIC program after NEW or a reset
@B	Disable the 1541 head rattle (64 mode only; @UJ re-enables it)
@C:new=old	Copy or combine files on the same disk
@Xdev, *"name"type	Set the destination drive and copy a file to it
@Gn	Set the sector interleave (0 restores the JiffyDOS default)
@UJ	Reset the drive
CTRL+D	Toggle the default drive between devices 8 and 9
CTRL+P	Print the text screen to a printer on device 4

Compatibility

• CMD says JiffyDOS loads and runs virtually all software, including copy-protected programs, and knew of "only a few heavily copy-protected games" that would not load. For those, switch to the stock ROMs.
• A tape drive cannot be used while the JiffyDOS Kernal is selected; tape access gives ILLEGAL DEVICE NUMBER ERROR. Switch to the stock Kernal to use tapes.
• The JiffyDOS commands work with Commodore's RAMDOS for the 1700, 1750 and 1764 REUs (RAMDOS 4.2 or later in 64 mode, 4.3 or later in 128 mode). Do not load the DOS Wedge from the RAMDOS disk, and do not use @L or the £ command with RAMDOS.
• Each JiffyDOS command opens a 255-byte buffer at the top of BASIC memory; a program that fills memory may give OUT OF MEMORY, which CLR usually cures.

Licensing

RETRO Innovations states that Mark Fellows created JiffyDOS and joined with CMD to market it. When CMD left the Commodore market the rights stayed with Fellows, who still holds the copyright. RETRO Innovations has a master licence from him and works with other licensees. Its page lists the authorised sales channels as Restore Store (ROMs, including country-specific versions), Coprolite Computer By-Products ("switchless" ROMs), Custom Commodores and RETRO Innovations itself, and says no other distributor is licensed. It also says JiffyDOS is neither public domain nor orphanware.

Related pages

• Commodore 64
• Jump-less Dual-Kernal Switcher
• Commodore 64 Power-Supply Protector (C64 Saver)
• Commodore Test Cartridge Index