KERNAL is
Commodore
Commodore may refer to:
Ranks
* Commodore (rank), a naval rank
** Commodore (Royal Navy), in the United Kingdom
** Commodore (United States)
** Commodore (Canada)
** Commodore (Finland)
** Commodore (Germany) or ''Kommodore''
* Air commodore ...
's name for the
ROM
Rom, or ROM may refer to:
Biomechanics and medicine
* Risk of mortality, a medical classification to estimate the likelihood of death for a patient
* Rupture of membranes, a term used during pregnancy to describe a rupture of the amniotic sac
* ...
-resident
operating system
An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs.
Time-sharing operating systems schedule tasks for efficient use of the system and may also in ...
core in its
8-bit
In computer architecture, 8-bit Integer (computer science), integers or other Data (computing), data units are those that are 8 bits wide (1 octet (computing), octet). Also, 8-bit central processing unit (CPU) and arithmetic logic unit (ALU) arc ...
home computers; from the original
PET
A pet, or companion animal, is an animal kept primarily for a person's company or entertainment rather than as a working animal, livestock, or a laboratory animal. Popular pets are often considered to have attractive appearances, intelligence ...
of 1977, followed by the extended but strongly related versions used in its successors: the
VIC-20
The VIC-20 (known as the VC-20 in Germany and the VIC-1001 in Japan) is an 8-bit home computer that was sold by Commodore Business Machines. The VIC-20 was announced in 1980, roughly three years after Commodore's first personal computer, the PE ...
,
Commodore 64
The Commodore 64, also known as the C64, is an 8-bit home computer introduced in January 1982 by Commodore International (first shown at the Consumer Electronics Show, January 7–10, 1982, in Las Vegas). It has been listed in the Guinness ...
,
Plus/4,
C16, and
C128.
Description
The Commodore 8-bit machines' KERNAL consists of the low-level, close-to-the-hardware OS routines roughly equivalent to the
BIOS
In computing, BIOS (, ; Basic Input/Output System, also known as the System BIOS, ROM BIOS, BIOS ROM or PC BIOS) is firmware used to provide runtime services for operating systems and programs and to perform hardware initialization during the ...
in IBM PC compatibles (in contrast to the
BASIC interpreter
A BASIC interpreter is an interpreter that enables users to enter and run programs in the BASIC language and was, for the first part of the microcomputer era, the default application that computers would launch. Users were expected to use the BAS ...
routines, also located in ROM) as well as higher-level, device-independent I/O functionality, and is user-callable via a
jump table
In computer programming, a branch table or jump table is a method of transferring program control ( branching) to another part of a program (or a different program that may have been dynamically loaded) using a table of branch or jump instruction ...
in RAM whose central (oldest) part, for reasons of backwards compatibility, remains largely identical throughout the whole 8-bit series. The KERNAL ROM occupies the last 8
KB of the 8-bit CPU's 64 KB address space ($E000–$FFFF).
The jump table can be modified to point to user-written routines, for example rewriting the screen display routines to display animated graphics or copying the character set into RAM. This use of a jump table was new to small computers at the time.
The
Adventure International
Adventure International was an American video game publishing company that existed from 1979 until 1986. It was started by Scott and Alexis Adams. Their games were notable for being the first implementation of the adventure genre to run on a ...
games published for the VIC-20 on cartridge are an example of software that uses the KERNAL. Because they only use the jump table, the games can be
memory dump
In computing, a core dump, memory dump, crash dump, storage dump, system dump, or ABEND dump consists of the recorded state of the working memory of a computer program at a specific time, generally when the program has crashed or otherwise termina ...
ed to disk, loaded into a Commodore 64, and run without modification.
The KERNAL was initially written for the Commodore PET by
John Feagans, who introduced the idea of separating the BASIC routines from the operating system. It was further developed by several people, notably
Robert Russell, who added many of the features for the VIC-20 and the C64.
Example
A simple, yet characteristic, example of using the KERNAL is given by the following
6502
The MOS Technology 6502 (typically pronounced "sixty-five-oh-two" or "six-five-oh-two") William Mensch and the moderator both pronounce the 6502 microprocessor as ''"sixty-five-oh-two"''. is an 8-bit microprocessor that was designed by a small te ...
assembly language
In computer programming, assembly language (or assembler language, or symbolic machine code), often referred to simply as Assembly and commonly abbreviated as ASM or asm, is any low-level programming language with a very strong correspondence be ...
subroutine (written in
ca65 assembler format/syntax):
CHROUT = $ffd2 ; CHROUT is the address of the character output routine
CR = $0d ;
PETSCII
PETSCII (''PET Standard Code of Information Interchange''), also known as CBM ASCII, is the character set used in Commodore Business Machines (CBM)'s 8-bit home computers, starting with the PET from 1977 and including the C16, C64, C116, C1 ...
code for Carriage Return
;
hello:
ldx #0 ; start with character 0 by loading 0 into the x index register
next:
lda message,x ; load byte from address message+x into the accumulator
beq done ; if the accumulator holds zero, we're done and want to branch out of the loop
jsr CHROUT ; call CHROUT to output char to current output device (defaults to screen)
inx ; increment x to move to the next character
bne next ; loop back while the last character is not zero (max string length 255 bytes)
done:
rts ; return from subroutine
;
message:
.byte "
Hello, world!"
.byte CR, 0 ; Carriage Return and zero marking end of string
This code stub employs the
CHROUT
routine, whose address is found at address
$FFD2
(65490), to send a text string to the default output device (e.g., the display screen).
The name
The KERNAL was known as ''kernel'' inside of Commodore since the PET days, but in 1980 Robert Russell misspelled the word as ''kernal'' in his notebooks. When Commodore technical writers Neil Harris and Andy Finkel collected Russell's notes and used them as the basis for the VIC-20 programmer's manual, the misspelling followed them along and stuck.
According to early Commodore myth, and reported by writer/programmer
Jim Butterfield
Frank James "Jim" Butterfield (14 February 1936 – 29 June 2007), was a Toronto-based computer programmer, author, and television personality known for his work with early microcomputers. He is particularly noted for associations with Commodore ...
among others, the "word" KERNAL is an acronym (or maybe more likely, a
backronym
A backronym is an acronym formed from an already existing word by expanding its letters into the words of a phrase. Backronyms may be invented with either serious or humorous intent, or they may be a type of false etymology or folk etymology. The ...
) standing for ''Keyboard Entry Read, Network, And Link'', which in fact makes good sense considering its role.
Berkeley Softworks
Berkeley most often refers to:
*Berkeley, California, a city in the United States
**University of California, Berkeley, a public university in Berkeley, California
* George Berkeley (1685–1753), Anglo-Irish philosopher
Berkeley may also refer ...
later used it when naming the core routines of its GUI OS for 8-bit home computers: the
GEOS KERNAL.
On device-independent I/O
Surprisingly, the KERNAL implemented a device-independent I/O API not entirely dissimilar from that of
Unix
Unix (; trademarked as UNIX) is a family of multitasking, multiuser computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, and ot ...
or
Plan-9, which nobody actually exploited, as far as is publicly known. Whereas one could reasonably argue that "everything is a file" in these latter systems, others could easily claim that "everything is a
GPIB Glycoprotein Ib (GPIb), also known as CD42,
is a component of the GPIb-V-IX complex on platelets. The GPIb-V-IX complex binds von Willebrand factor, allowing platelet adhesion and platelet plug formation at sites of vascular injury.
It is defici ...
-device" in the former.
Due to limitations with the 6502 architecture at the time, opening an I/O channel requires three system calls. The first typically sets the logical filename through the
SETNAM
system call. The second call,
SETLFS
, establishes the GPIB/IEEE-488 "device" address to communicate with. Finally
OPEN
is called to perform the actual transaction. The application then used
CHKIN
and
CHKOUT
system calls to set the application's current input and output channels, respectively. Applications may have any number of concurrently open files (up to some system-dependent limit; e.g., the C64 allows for ten files to be opened at once). Thereafter,
CHRIN
and
CHROUT
prove useful for actually conducting input and output, respectively.
CLOSE
then closes a channel.
Observe that no system call exists to "create" an I/O channel, for devices cannot be created or destroyed dynamically under normal circumstances. Likewise, no means exists for seeking, nor for performing "I/O control" functions such as
ioctl
In computing, ioctl (an abbreviation of input/output control) is a system call for device-specific input/output operations and other operations which cannot be expressed by regular system calls. It takes a parameter specifying a request code; th ...
() in Unix. Indeed, the KERNAL proves much closer to the Plan-9 philosophy here, where an application would open a special "command" channel to the indicated device to conduct such "meta" or "out-of-band" transactions. For example, to delete ("scratch") a file from a disk, the user typically will "open" the resource called
S0:THE-FILE-TO-RMV
on device 8 or 9, channel 15. Per established convention in the Commodore 8-bit world, channel 15 represents the "command channel" for peripherals, relying on message-passing techniques to communicate both commands and results, including exceptional cases. For example, in
Commodore BASIC
Commodore BASIC, also known as PET BASIC or CBM-BASIC, is the dialect of the BASIC programming language used in Commodore International's 8-bit home computer line, stretching from the PET of 1977 to the C128 of 1985.
The core is based on 6502 M ...
, they might find software not unlike the following:
70 ...
80 REM ROTATE LOGS CURRENTLY OPENED ON LOGICAL CHANNEL #1.
90 CLOSE 1
100 OPEN 15,8,15,"R0:ERROR.1=0:ERROR.0":REM RENAME FILE ERROR.0 TO ERROR.1
110 INPUT# 15,A,B$,C,D:REM READ ERROR CHANNEL
120 CLOSE 15
130 IF A=0 THEN GOTO 200
140 PRINT "ERROR RENAMING LOG FILE:"
150 PRINT " CODE: "+A
160 PRINT " MSG : "+B$
170 END
200 REM CONTINUE PROCESSING HERE, CREATING NEW LOG FILE AS WE GO...
210 OPEN 1,8,1,"0:ERROR.0,S,W"
220 ...
Device numbers, per established documentation, are restricted to the range
,16 However, this limitation came from the specific adaptation of the IEEE-488 protocol and, in effect, applies only to external peripherals. With all relevant KERNAL system calls vectored, programmers can intercept system calls to implement virtual devices with any address in the range of
2,256 Conceivably, one can load a device driver binary into memory, patch the KERNAL I/O vectors, and from that moment forward, a new (virtual) device could be addressed. So far, this capability has never been publicly known as utilized, presumably for two reasons: (1) The KERNAL provides no means for dynamically allocating device IDs, and (2) the KERNAL provides no means for loading a relocatable binary image. Thus, the burden of collisions both in I/O space and in memory space falls upon the user, while platform compatibility across a wide range of machines falls upon the software author. Nonetheless, support software for these functions could easily be implemented if desired.
Logical filename formats tends to depend upon the specific device addressed. The most common device used, of course, is the floppy disk system, which uses a format similar to
MD:NAME,ATTRS
, where M is a flag of sorts ($ for directory listing, @ for indicating a desire to overwrite a file if it already exists, unused otherwise.), D is the (optional) physical disk unit number (0: or 1: for dual-drive systems, just 0: for single-disk units like the 1541, et al., which defaults to 0: if left unspecified),
NAME
is a resource name up to 16 characters in length (most characters allowed except for certain special characters), and
ATTRS
is an optional comma-separated list of attributes or flags. For example, if the user wants to overwrite a program file called
PRGFILE
, they might see a filename like
@0:PRGFILE,P
used in conjunction with device 8 or 9. Meanwhile, a filename for the RS-232 driver (device 2) consists simply of four characters, encoded in binary format.
[''Commodore 128 Programmers Reference Guide'', Commodore Business Machines, Inc., 1986, p. 382]
Other devices, such as the keyboard (device 0), cassette (device 1), the display interface (device 3), and printer (device 4 and 5), require no filenames to function, either assuming reasonable defaults or simply not needing them at all.
Notes
External links
Commodore KERNAL HistoryCommodore 64 KERNAL I/O Monitor Utility
{{Operating system
Operating system kernels
Commodore 64
Nonstandard spelling
1977 software