Difference between revisions of "GeneveOS Memory Management Functions"

From Ninerpedia
Jump to navigation Jump to search
Line 1: Line 1:
Memory management in MDOS is available via XOP 7. In the MDOS sources the relevant files are ''manage2s'' and ''manage2t''.
Memory management in MDOS is available via XOP 7. In the MDOS sources the relevant files are ''manage2s'' and ''manage2t''.


== General purpose XOPs ==
'''Fast RAM''' is all memory with 0 wait states (SRAM), while '''Slow RAM''' is 1 wait state RAM, offered by the DRAM chips. The on-chip RAM is not considered here as it is not manageable by MDOS. The 256 bytes of on-chip RAM are always visible in the logical address area F000-F0FB and FFFC-FFFF. Any page that is mapped to the E000-FFFF area will be overwritten by operations in that area; this must be considered when using the E000-FFFF area.


=== Return number of free pages in system ===
Two classes of memory management functions are available: XOPs for user tasks, and XOPs exclusively used by the operating system.
 
== Introduction and terms ==
 
=== Execution pages ===
 
=== Physical pages ===
 
=== Virtual pages ===
 
== User-task XOPs ==
 
=== Available memory pages ===


'''Opcode: 0'''
'''Opcode: 0'''
Line 26: Line 38:
|}
|}
   
   
=== Claim pages into local map from free pages ===
=== Allocate pages ===


'''Opcode: 1'''
'''Opcode: 1'''
Line 49: Line 61:
|}
|}


=== Return pages into free pool from local map ===
This function is used to claim pages from the set of unassigned physical pages. This is particularly useful when the application requires more than just small buffers. As it was common with TI application programming, buffers were usually placed statically in the program, that is, a portion of memory (like 256 bytes) was reserved in the program code to be used for storing data. Assembly language offers the [[BSS]] and [[BES]] directives for this purpose. This is not recommended when the buffer is very big, like 100 KiB. In that cases, dynamic allocation is the typical solution also known from other systems.
 
=== Free pages ===


'''Opcode: 2'''
'''Opcode: 2'''

Revision as of 12:57, 12 November 2011

Memory management in MDOS is available via XOP 7. In the MDOS sources the relevant files are manage2s and manage2t.

Fast RAM is all memory with 0 wait states (SRAM), while Slow RAM is 1 wait state RAM, offered by the DRAM chips. The on-chip RAM is not considered here as it is not manageable by MDOS. The 256 bytes of on-chip RAM are always visible in the logical address area F000-F0FB and FFFC-FFFF. Any page that is mapped to the E000-FFFF area will be overwritten by operations in that area; this must be considered when using the E000-FFFF area.

Two classes of memory management functions are available: XOPs for user tasks, and XOPs exclusively used by the operating system.

Introduction and terms

Execution pages

Physical pages

Virtual pages

User-task XOPs

Available memory pages

Opcode: 0

Input Output
R0 Opcode (0000) Error code (always 0)
R1 Number of free pages
R2 Number of fast free pages
R3 Total number of pages in system

Allocate pages

Opcode: 1

Input Output
R0 Opcode (0001) Error code (0, 1, 7, 8)
R1 Number of pages Number of pages actually fetched to complete map as required
R2 Local page address Number of fast pages fetched
R3 Speed flag (if not 0, only fast)

This function is used to claim pages from the set of unassigned physical pages. This is particularly useful when the application requires more than just small buffers. As it was common with TI application programming, buffers were usually placed statically in the program, that is, a portion of memory (like 256 bytes) was reserved in the program code to be used for storing data. Assembly language offers the BSS and BES directives for this purpose. This is not recommended when the buffer is very big, like 100 KiB. In that cases, dynamic allocation is the typical solution also known from other systems.

Free pages

Opcode: 2

Input Output
R0 Opcode (0002) Error code (0, 2)
R1 Number of pages
R2 Local page address

Error code 2 is returned when the local page address (R2) is 0; page 0 cannot be freed in this way.

Map local page at excution page

Opcode: 3

Input Output
R0 Opcode (0003) Error code (-, 2, 3)
R1 Local page number
R2 Execution page number

The local page numbers are the IDs of the allocated memory pages. The task contains a linked list of pointers to these local pages; the last list element points to 0. The list of pages is not sorted, so the search for a special local page may require to traverse the complete list.

Error code 2 is returned when the local page number or the execution page number is 0.

Error code 3 is returned when the execution page number is higher than 7 or the list does not contain an entry with the given local page number.

Get address map

Opcode: 4

Input Output
R0 Opcode (0004) Error code (-, 8)
R1 Pointer to buffer Count of pages reported
R2 Buffer size

On return of the call, the memory locations pointed to by R1 contain a sequence of physical page numbers that have been allocated. R1 contains the length of this sequence.

Error code 8 is returned when the buffer is too small to hold the list of numbers of allocated pages.

Declare shared pages

Opcode: 5

Input Output
R0 Opcode (0005) Error code
R1 Number of pages to declare as shared
R2 Local page address
R3 Type to be assigned to shared pages

Release shared pages (type)

Opcode: 6

Input Output
R0 Opcode (0006) Error code
R1 Type

Also have to check their current execution map

Get shared pages

Opcode: 7

Input Output
R0 Opcode (0007) Error code
R1 Type
R2 Local page number for start of shared area

Return size of shared page group

Opcode: 8

Input Output
R0 Opcode (0008) Error code
R1 Type Number of pages in shared group

Privileged XOPs (only available for operating system)

Release task

Opcode: 9

Input Output
R0 Opcode (0009)

Task header at >8000

Page get

Opcode: 10

Input Output
R0 Opcode (000A) Error code
R1 Page number to get (if high byte not 0, get first available) Pointer to node
R2 Speed flag (if not 0, only fast) Page number from node

Add page to free pages in system

Opcode: 11

Input Output
R0 Opcode (000B) Error code (if no free nodes available)
R1 Page number Pointer to node

Add a node to the list of free nodes

Opcode: 12

Input Output
R0 Opcode (000C) Error code (always 0000)
R1 Pointer to node

Link a node to the specified node

Opcode: 13

Input Output
R0 Opcode (000D) Error code (always 0000)
R1 Pointer to node
R2 Pointer to node to link to

Get address map (system)

Opcode: 14

Input Output
R0 Opcode (000E) Count of valid pages

Error codes

Code Meaning
00 No error
01 not enough free pages
02 can't remap execution page zero
03 no page at LOCAL address
04 user area not large enough for list
05 shared type already defined
06 shared type doesn't exist
07 can't overlay shared and private memory
08 out of table space
Retrieved from "http://www.ninerpedia.org/index.php?title=GeneveOS_Memory_Management_Functions&oldid=48031"