AMC-OS Loader Memory management

Memory used during AMC-OS Loader execution

AMC-OS Loader uses only the first megabyte of memory :

• 00000-003FF : Real-mode interrupt table
• 00400-00500 : BIOS static data
• 00501-005FF : Free (unused)
• 00600-007FF : Master boot record
• 00800-[__A] : Kernel static data (initialized by boot loader)
• [__A]-[__B] : AMC-OS Loader code
• [__B]-[__C] : AMC-OS Loader picture
• [__C]-077FF : Free for allocation
• 077FF-07BFF : AMC-OS Loader stack
• 07C00-07DFF : Boot loader code (VBR or MBR for floppy disk)
• 07E00-07FFF : Free (unused)
• 08000-9[_D] : Free for allocation
• 9[_D]-09FFF : Extended BIOS data area (EBDA - optional)

Memory management

Initialization

During memory initialization process (AMCOSLDR_InitFirstMegabyte), AMC-OS Loader :

• looks for EBDA using interrupt 12H and value stored in 0040:000E to get highest pointer in memory [_D]
• calculates the values of [__A] to get lowest pointer in memory
• creates a linked list of available blocks of memory (AMCOSLDR_Malloc_Entry)
• initializes two blocks of available memory (marked Free for allocation in previous table)

Allocation

Three functions are available to AMC-OS Loader for memory allocation :

• AMCOSLDR_DefinitiveAlloc : Used to allocate memory that shall stay at this place at the end of the process (used by kernel afterwards). Memory will be taken from bottom of free memory.
• AMCOSLDR_TempAlloc : Used to allocate memory that will be freed at the end of the process (eraseable by kernel afterwards). Memory will be taken from top of free memory.
• AMCOSLDR_VolatileAlloc : Used to allocate memory for immediate use (valid only until a new call to any memory function is made). Memory will be taken from top of free memory.

The two first functions maintains the linked list of available blocks of memory.