The 'nucleus' of the Xtal system is a set of subroutines in the file aa.r which perform all of the system control functions. These functions are used frequently in all Xtal software and a good knowledge of them is essential for a program developer. The subroutines are named as AAnn where nn are sequence numbers. They are grouped into the following broad classifications:

General system control and line input/output	AA00-AA09
Binary file input/output	AA10-AA19
Master archive file input/output	AA20-AA29
General file and move facilities	AA50-AA59
Machine-specific time/date/Boolean routines	AA70-AA74

The nucleus routines are either called internally or by non-nucleus routines. Reference by external software usuall involves the use of system 'convenience' Xtal macros. Here is a list of the nucleus subroutines supplied with Xtal3.2 with their macro names.

Routine	Function	Macro name
AA00	Calculation scheduler (Main program)	-
AA01	Read and process line data as characters	readline:
AA02	Convert char. data from AA01 to field data	dcodefld:
AA03	Convert field data to character data (format)	ncodefld:
AA04	Write and paginate line data as characters	writeline:
AA05	Process, identify and strip an atom label	label:
AA06	Error reporting and system exit	iquit:
AA07	System common initialisation	initcom:
AA08	Program initialisation and timing	initprg:
AA09	Compare char string with table of char strings	compchar:
AA10	Copy complete bdf from one name to another	copybdf:
AA11	Write specific packets of a bdf	writepkt:
AA12	Read and write specific packets of a bdf	readwpkt:
AA13	Copy specific logical records from one bdf to another	copyfile:
AA14	Sequential binary file device handler	rewindbdf:
AA15	Read and construct directory packets of bdf	indexpkt:
AA50	Open all files	open*:
AA51	Move strings of real words	movereal:
AA52	Move single packed word	movpakwd:
AA53	Compare single packed word	compakwd:
AA54	Read a single line of characters	linein:
AA55	Move char string to char string	movechar:
AA56	Move char string to real string	movector:
AA57	Move real string to char string	movertoc:
AA58	Convert case of char string	upcase: / locase:
AA70	Get compute time in real seconds	getcpus:
AA71	Get clock time as string 'hh:mm:ss'	gettime:
AA72	Get date as numerical day, month and year	getdate:
AA73	Pack integer into real word	intpak:
AA74	Unpack integer from real word	intunpak:

Here is a developers guide on how to use the system nucleus functions.