AMC-OS Loader Memory management: Difference between revisions
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* <code>AMCOSLDR_TempAlloc</code> : 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. | * <code>AMCOSLDR_TempAlloc</code> : 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. | ||
* <code>AMCOSLDR_VolatileAlloc</code> : 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. | * <code>AMCOSLDR_VolatileAlloc</code> : 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. | ||
All functions waits for the requested size in | All functions waits for the requested size in segment size (16-bytes unit), and returns a segment of memory aligned on 512 bytes boundaries to facilitate disk operations. | ||
The two first functions maintains the linked list of available blocks of memory. | The two first functions maintains the linked list of available blocks of memory. | ||
Revision as of 17:51, 13 April 2020
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.
All functions waits for the requested size in segment size (16-bytes unit), and returns a segment of memory aligned on 512 bytes boundaries to facilitate disk operations.
The two first functions maintains the linked list of available blocks of memory.