[GSoC] Defining Memory for MMU page tables at CSB337

[Gedare Bloom]

Whether defined statically or allocated dynamically the access time
should not differ. The main issue would be whether you would need the
memory available before bringing up the RTEMS Workspace. I don't think
this is the case, so you could allocate the region from
Workspace_Allocate.

All targets support dynamic allocation via malloc. The setting of
HeapSize=0 is misleading; probably the actual size is determined
during boot by the BSP's 'get workspace' function. Usually the BSP is
given the 'rest' of the memory after static sizes for code and data
are determined, and some BSPs will split this remainder between Heap
and Workspace (RTEMS kernel internal heap), or will provide a shared
(unified) heap and workspace that satisfies allocations to each. RTEMS
Workspace size is bounded based on how the user application configures
the kernel, so at runtime the BSP can determine how much space to
reserve for the workspace and give the rest to the C program heap
(malloc).

-Gedare

On Sat, Aug 4, 2012 at 5:14 PM, Hesham Moustafa
<heshamelmatary at gmail.com> wrote:
> I intended to dynamically allocate memory for it, but i thought it would be
> faster to define an area for lvl2 page tables to access/allocate them
> faster. I just want to be sure that CSB337 implement malloc. I noticed that
> line at linker script for CSB337
>
> HeapSize = 0;
>
> that why i am inquiring about that issue.
>
> thanks,
> Hesham
>
>
> On Sat, Aug 4, 2012 at 11:02 PM, Joel Sherrill <Joel.Sherrill at oarcorp.com>
> wrote:
>>
>> Does it have to be placed in the linker script?
>>
>> Can you dynamically allocate it as the properly needed size?
>> ________________________________________
>> From: rtems-devel-bounces at rtems.org [rtems-devel-bounces at rtems.org] On
>> Behalf Of Hesham Moustafa [heshamelmatary at gmail.com]
>> Sent: Saturday, August 04, 2012 7:52 AM
>> To: rtems-devel at rtems.org
>> Subject: [GSoC] Defining Memory for MMU page tables at CSB337
>>
>> Hi,
>>
>> I want to define memory for page tables at CSB337 BSP.
>>
>> The following is quoted from lincmds.csb337
>>
>> MEMORY {
>> SDRAM_MMU : ORIGIN = 0x20100000, LENGTH = 16k
>> SDRAM : ORIGIN = 0x20104000, LENGTH = 15M - 16k
>> SRAM : ORIGIN = 0x00200000, LENGTH = 16k
>> NIRVANA : ORIGIN = 0, LENGTH = 0
>> }
>>
>> That only allocate page table for level 1 page table which is 16 k ( each
>> entry represents 1M page of memory). I'd like to add level 2 page tables to
>> represent 4k pages. A level-2 page table consists of 256 entry and consumes
>> 1K of memory and its base address is installed at level-1 page table entry.
>>
>> The question is what's the proper size of level-2 page tables to reserve
>> from memory and what should be its base address (ORIGIN) to be written at
>> that linker script ?
>>
>> Thanks,
>> Hesham
>
>
>
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