Memory initialization - Revision history

Kindman: /* First megabyte */

2022-09-10T23:13:52Z

First megabyte

← Older revision		Revision as of 01:13, 11 September 2022
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	\|}		\|}
	All reclaimable memory is added to the SMALLOC structures of AMC-OS Loader, than will be analyzed by Kernel.		All reclaimable memory is added to the SMALLOC structures of AMC-OS Loader, than will be analyzed by Kernel.

			End of 1st megabyte, segment-like, [_D] or A000H is stored in <code>MEMORY_BaseMaxSegment</code>.

	=Kernel start=		=Kernel start=

	~~When~~ Kernel ~~starts,~~ AMC-OS uses information discovered by the loader to build memory structures.		Process of memory initialization by Kernel is the following :

			* Initialization of 1st MB of memory : AMC-OS uses information discovered by the loader to build initial memory structures.
			* A20 gate unlocking to access memory above 1MB
			* Initialization of all physical memory

	==~~First~~ megabyte==		==Initialization of first megabyte==
	Kernel starts by calling <code>INIT_MemoryUsableIn1stMeg</code>. The function determines the first address of free memory in the first megabyte, just after kernel relocation code and below EBDA.		Kernel starts by calling <code>INIT_MemoryUsableIn1stMeg()</code>. The function determines the first address of free memory in the first megabyte, just after kernel relocation code and below EBDA. It checks that it matches with AMC-OS Loader MALLOC structure, as its last allocatable block should start just after kernel relocation code.

	The function fills :		The function fills :
	* <code>MEMORY_FreePageAddrIn1stMeg</code>		* <code>MEMORY_FreePageAddrIn1stMeg</code>
	* <code>MEMORY_FreePagesIn1stMeg</code>		* <code>MEMORY_FreePagesIn1stMeg</code>
			which allow the call to <code>INIT_AllocatePagesBelow()</code> for allocation of contiguous pages of memory during initialization.

			It also calls <code>INIT_MemorySmallocInit</code>, which rebuilds AMC-OS Loader SMALLOC structures with 32-byte direct offsets to have a quick function for small memory allocation during memory initialization : <code>INIT_MemoryDefinitiveAlloc()</code> .

			At this point, all unused memory by AMC-OS Loader is reclaimed by kernel, and 1st megabyte of memory is fully analyzed.

	==A20 Gate==		==A20 Gate==

Kindman: /* During AMC-OS Loader */

2022-09-10T22:59:26Z

During AMC-OS Loader

← Older revision		Revision as of 00:59, 11 September 2022
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	\|BIOS static data (for V86)		\|BIOS static data (for V86)
	\|-		\|-
	\|<code>00501-~~005FF~~</code>		\|<code>00501-007FF</code>
	\|Partially allocated memory by <code>AMCOSLDR_DefinitiveAlloc</code>		\|Partially allocated memory by <code>AMCOSLDR_DefinitiveAlloc</code>
	\|-
	~~\|<code>00600-007FF</code>~~
	~~\|''Master boot record (no longer used - reclaimable)''~~
	\|-		\|-
	\|<code>00800-[__A]</code>		\|<code>00800-[__A]</code>
	\|Kernel static data		\|Kernel static data
	\|-		\|-
	\|<code>[__A~~]-[__B]</code>~~		\|<code>[__A]-077FF</code>
	~~\|AMC-OS Loader code (''no longer used - reclaimable'')~~
	\|-
	~~\|<code>[__B]-[__C]</code>~~
	~~\|AMC-OS Loader picture (''no longer used - reclaimable'')~~
	\|-
	~~\|<code>[__C~~]-077FF</code>
	\|Partially allocated memory by <code>AMCOSLDR_DefinitiveAlloc</code>		\|Partially allocated memory by <code>AMCOSLDR_DefinitiveAlloc</code>
	\|-		\|-

Kindman: Added memory map after execution of AMC-OS Loader

2022-09-10T22:57:57Z

Added memory map after execution of AMC-OS Loader

@@ Line 9: / Line 9: @@
 * Get configured size of extended memory in CMOS
 Depending on functions supported by BIOS, map will be more or less precise, and memory might be lost if ISA Hole in the 15-16M area is configured.
 =Kernel start=

Kindman at 16:47, 18 April 2020

2020-04-18T16:47:37Z

← Older revision		Revision as of 18:47, 18 April 2020
Line 26:		Line 26:

	A20 gate was controlled by keyboard controller on AT+. To allow compatibility with 8086/8088, the A20 address line was forced to 0 on AT computers, blocking access to memory above 1MB. A20 gate must be enabled to allow A20 address line to be used normally.		A20 gate was controlled by keyboard controller on AT+. To allow compatibility with 8086/8088, the A20 address line was forced to 0 on AT computers, blocking access to memory above 1MB. A20 gate must be enabled to allow A20 address line to be used normally.

			==Physical memory initialization==
			Physical memory is initialized by calling <code>INIT_GlobalMemory</code>.

			===Memory map===
			The function first builds a map of physical memory :
			* If available, it relies first on type-1 (available) entries of E820 BIOS records. ''In current release, memory above 4GB is ignored''.
			* If available, it relies on E801 BIOS call results to determine a block of memory below 16MB and a block of memory above 16MB.
			* In other cases, kernel do a manual probing of available memory, using function <code>INIT_MemoryCheckSegment</code>.

Kindman at 16:39, 18 April 2020

2020-04-18T16:39:49Z

@@ Line 1: / Line 1: @@
-==During AMC-OS Loader==
+=During AMC-OS Loader=
 To get size and map of memory, AMC-OS Loader now relies mainly on BIOS instead of probing, which was the preferred way in AMC-OS <2.10.
@@ Line 11: / Line 11: @@
 Depending on functions supported by BIOS, map will be more or less precise, and memory might be lost if ISA Hole in the 15-16M area is configured.
-==Kernel start==
+=Kernel start=

Kindman: Created page with "==During AMC-OS Loader== To get size and map of memory, AMC-OS Loader now relies mainly on BIOS instead of probing, which was the preferred way in AMC-OS <2.10. AMC-OS Loade..."

2020-04-18T15:28:51Z

Created page with "==During AMC-OS Loader== To get size and map of memory, AMC-OS Loader now relies mainly on BIOS instead of probing, which was the preferred way in AMC-OS <2.10. AMC-OS Loade..."

New page

==During AMC-OS Loader==

To get size and map of memory, AMC-OS Loader now relies mainly on BIOS instead of probing, which was the preferred way in AMC-OS <2.10.

AMC-OS Loader proceed this way :
* Try INT 15H, function E820 to get memory map.
* Try INT 15H, function E801 to get size of memory below 16MB and above 16MB
* Try INT 15H, function 88 to get effective size of extended memory
* Get configured size of extended memory in CMOS

Depending on functions supported by BIOS, map will be more or less precise, and memory might be lost if ISA Hole in the 15-16M area is configured.

==Kernel start==