F$All64

Allocate 64	Dynamically allocates 64-byte blocks of memory
OS9 F$All64 103F 30

Entry Conditions

X base address of the page table; 0 = the page table has not been allocated

Exit Conditions

A block number

X base address of the page table

Y address of the block

Error Output

CC carry set on error

B error code, if any

Additional Information

• The Allocate 64 system call allocates the 64-byte blocks of memory by splitting pages (256-byte sections) into four sections.
• NitrOS-9 uses the first 64 bytes of the base page as a page table. This table contains the page number (most significant byte of the address) of all pages in the memory structure. If Register X passes a value of zero, the call allocates a new base page and the first 64-byte memory block.
• Whenever a new page is needed, a Request System Memory system call (F$SRqMem) executes automatically.
• The first byte of each block contains the block number. Routines that use the Allocate 64 call should not alter this byte.
• The following diagram shows how seven blocks might be allocated:

	Any Memory Page		Any Memory Page
Base Page -->
	Page Table(64 bytes)		XBlock 4(64 bytes)
	XBlock 1(64 bytes)		XBlock 5(64 bytes)
	XBlock 2(64 bytes)		XBlock 6(64 bytes)
	XBlock 3(64 bytes)		XBlock 7(64 bytes)

krnp2