TLSF Dynamic Memory Allocation
Inhaltsverzeichnis
Overview
TLSF (Two-Level Segregated Fit) is a dynamic memory allocator suited for real-time systems. It is a good-fit algorithm with a bound response time O(1) for any number of managed memory blocks.
Free blocks of memory are organized in lists each containing blocks of a specific size range. Requested blocks are searched in the list with sizes equal or greater the requested size, remaining memory is split up if neccessary and sorted back into the list. Freed blocks are merged with neighboring free blocks and also put back into the list.
The remaining memory from the end of global declared variables to the start of the stack spaces and also external memory (Xram), if available, is managed by the library (configurable).
How to use it
Setup
Create an inc subfolder to your project and copy the files os_common.inc, os_memory.inc and os_malloc_tlsf.inc into the folder.
Include the library:
' any const option must be placed above the file include Const Os_mem_free_start = ### ' mandatory $include "inc\os_malloc_tlsf.inc"
The start adress of the free memory area can not be determined automatically (Bascom-AVR 2.0.8.1). It can be found by examining the compile report (with setting Options->Compiler->Output->Show internal variables enabled), the last variable (with the highest adress) plus the byte size is the adress of the first unused byte.
Compiler report example
Here is a (shortened) example of a compiler report, and where the address could be found. In this example, the RAM start address should be set to at least 169 dec.
Report : chronos Date : 05-20-2013 Time : 01:54:06 Compiler : BASCOM-AVR LIBRARY V 2.0.7.6 Processor : M32 SRAM : 800 hex EEPROM : 400 hex ROMSIZE : 8000 hex ... -------------------------------------------------------------------------------- Variable Type Address(hex) Address(dec) -------------------------------------------------------------------------------- ... OS_CRITICAL_NESTING_LEVEL Byte 0060 96 OS_EVENT_TASK Word 0061 97 MALLOC_FREE_POINTER Word 0063 99 OS_SCHED_RUNNING_WEIGHT Byte 0065 101 OS_SCHED_LIST_HEAD Word 0066 102 OS_SCHED_PREEMPTED_TASK Word 0068 104 OS_TASK_ACTIVE Word 006A 106 OS_TASK_TEMPBYTE_ISR Byte 006C 108 OS_TASK_TEMPWORD_ISR Word 006D 109 OS_TASK_TEMPWORD2_ISR Word 006F 111 OS_TIMER_SYSTEMTIME Dword 0071 113 OS_TIMER_LISTHEAD Word 0075 117 OS_TIMER_NEXT_EVENT Word 0077 119 OS_TIMER_ELAPSED_TIME Word 0079 121 OS_TIMER_ENABLE_KERNEL Byte 007B 123 OS_INT_TABLE Word (20) 007C 124 TASKOBJECT Word 00A4 164 TASK_1_COUNTER Byte 00A6 166 TASK_2_COUNTER Byte 00A7 167 ___LCDCOUNTER Byte 00A8 168 <--- -------------------------------------------------------------------------------- Constant Value -------------------------------------------------------------------------------- SREG &H3F SPH &H3E SPL &H3D ...
Managing memory
The library works with memory adresses. If a memory request of given size can be served (consecutive block of free memory has been found), the adress of the start of the block is returned. For a size request bigger than what is managed by the algorithm, as fallback a simple search for a block of suitable size through the last list will be performed (O(n)). If the request can't be fullfilled, the value 0 is returned. The application has to check for that return value and react accordingly, it is also responsible not to write outside of the requested block of memory. Allocated memory is NOT cleared (set to 0) by the library.
With no external memory, 16 bit adress width (Word variable type) is used, with external memory 24 bits are used (DWord type).
Dim Myblockofmemory As [Word/Dword] Myblockofmemory = Malloc([Size]) If Myblockofmemory = 0 Then ' memory allocation error handling (not enough free memory) End If
When the block is no longer needed, it must be returned to the free memory pool by calling:
Free Myblockofmemory
Interface description
The following constants have to be defined prior to including the library. The values shown here are default values if the constant is not defined by the user.
Const Os_mem_free_start = [&H200/with XRAM: &H2000]
MANDATORY parameter, as described in Setup. For reasons, it has also default values.
Const Os_tlsf_fli_offset = 4
Start of first level block size ranges in powers of 2. Size = 2 ^ (Os_tlsf_fli_offset + 1); with a default value of 4, first level sizes start at 32.
Const Os_tlsf_max_fli = [10/with XRAM: 12]
End of first level block size ranges. Size = 2 ^ Os_tlsf_max_fli; defaults without XRAM to 1024, with XRAM to 4096.
Const Os_tlsf_max_log2_sli = 3
Log2 of Second level range count (max. 3). Since the search process is speed up by using bitmaps, this value should match the platform's word width. For 8-Bit AVR it is 2 ^ 3 = 8.
These 3 parameters result in the following block size ranges (default values, no XRAM):
First level | Second level (+4+1) | 0 1 2 3 4 5 6 7 -------------------------------------------------------------------------- 0 | 32 | 0 4 8 12 16 20 24 28 1 | 64 | 32 36 40 44 48 52 56 60 2 | 128 | 64 72 80 88 96 104 112 120 3 | 256 | 128 144 160 176 192 208 224 240 4 | 512 | 256 288 320 352 384 416 448 480 5 | 1024 | 512 576 640 704 768 832 896 960
Index 0 is not used, Index 1 is a list containing blocks up to a size of 4 Bytes, Index 2 list has sizes from 4 to 8 Bytes, Index 8 contains 16-32 Byte blocks, ...
Const Debug_level_tlsf = 0
Set debug output verbosity, 0 = no debug, 1 = Print out available memory each Malloc/Free, 2 = Print out memory pool overview, 3 = Print additional info during Malloc/Free. If debug outputs are activated, option Os_task_debug_metrics is also declared.
Const Os_task_dbg_metrics = 0
Declare Const (value doesn't matter) to enable tracking of available memory. If activated, a variable will be created:
#if Os_big_ram = False Dim Available_memory As Word #else Dim Available_memory As Dword #endif
#if Os_big_ram = False Function Malloc(byval Size As Word) As Word #else Function Malloc(byval Size As Dword) As Dword #endif
Request a block of memory of given size. Returns the starting memory adress or zero if not enough free memory left.
#if Os_big_ram = False Sub Free(byref Block As Word) #else Sub Free(byref Block As Dword) #endif
Returns a previously allocated block to the free memory pool.
#if Os_big_ram = False Function Os_malloc_blocksize(byref Block As Word) As Word #else Function Os_malloc_blocksize(byref Block As Dword) As Dword #endif
Returns the size of a block.
Sub Os_malloc_clear()
Empties all lists, resets the allocator
Sub Os_malloc_init()
Initializes the allocator. This is done when the library is included, in standard applications, it is not needed to call. However, to reset the allocator, use Os_malloc_clear before calling Os_malloc_init.
Samples
WIP
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Change log
Version 0.1 (##.##.2019)
- Initial release.
