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be carefull of getting into cache coherency problems!!! you might get rando=
m data in L2!

Chekib
----- Message d'origine ----
De : "s...@hotmail.com" <s...@hotmail.com>
=C3=80 : c...@yahoogroups.com
Envoy=C3=A9 le : Mercredi, 12 Mars 2008, 22h35mn 16s
Objet : [c6x] Ext Memory access without EDMA

                              Hi everyone,
=20
 Is it possible to access external memory without using EDMA. I would like =
to pass a buffer pointer located in external memory to a function call with=
out configuring EDMA. The DSP i am using is C6713. I would configure whole =
L2 as SRAM (256K) i.e., no L2 cache.
=20
 Any comment will be appreciated.
=20
 Thanks
=20
 Sankar Barua
=20
Check Out Industry's First Single-Chip, Multi-Format, Real-Time HD Video Tr=
anscoding Solution for Commercial & Consumer End Equipment: www.ti.com/dm64=
67

=20

(You need to be a member of c6x -- send a blank email to c6x-subscribe@yahoogroups.com )

The great thing about disabling the L2 cache is that you don't have to 
worry about cache interactions.  If you have disabled the cache, you've 
got access to 256k of internal ram to work with, and can directly access 
whatever external ram you have available wherever it is addressed.

I'm working with two boards, one has 1Mbyte of external SBSRAM located 
at 0x80000000 and the other has 32Mbytes of SDRAM located at the same 
starting position. Since my program is currently written to be able to 
work on both boards using cache, I've got my linker config set up as 
follows. I declare the cache here, just so that I won't forget that the 
ram is used. My system boots a bios that takes the first 0x1300 bytes of 
ram.

MEMORY
{
    L2RAM    : org = 0x00001300, len = 0x0002ED00
    CACHE    : org = 0x00030000, len = 0x00010000
    SRAM    : org = 0x80000000, len = 0x00100000  /* First Megabyte of 
ram exists on both old and new boards */
    SRAMEX  : org = 0x80100000, len = 0x01F00000  /* new boards have 
twice the RAM that the original boards had */
    /* V1 Board Samsung K6X8016T3B-TF55     512*1024*16 bits */
    /* V2 Board Samsung K4S561632E-TI75 16*1024*1024*16 bits */
}

Then my sections portion of the linker config allocates things into the 
memory locations that I want to use. You can see how I'm splitting the 
.text and .far sections into both internal and external ram as the 
linker wants to.  (I've actually got more sections defined, as I have 
code that I explicitly want in internal and external memory.  I have 
those declared initially and just let the linker take care of what's 
left. It is really amazing how slow external ram is compared to the L2 
Ram, as well as how much improvement the cache can provide. 

The comments that I've included about each of the sections were copied 
directly from TI documentation. I include them for reference purposes only.

SECTIONS
{
    .stack    > L2RAM
    .sysmem    > L2RAM    /* The .sysmem section reserves space for 
dynamic memory allocation. The reserved space is used by the malloc, 
calloc, and realloc functions. If a C/C++ program does not use these 
functions, the compiler does not create the .sysmem section. */
    .cio    > L2RAM
    .switch    > L2RAM    /* The .switch section contains tables for 
large switch statements. */
    .data    > L2RAM    /* .data is not used by the C compiler    */
    .bss    > L2RAM    /* The .bss section reserves space for global and 
static variables. When you specify the -c linker option, at program 
startup, the C/C++ boot routine copies data out of the .cinit section 
(which can be in ROM)  it in the .bss section. The compiler defines the 
global symbol $bss and assigns $bss the value of the starting address of 
the .bss section. */
    .text    >> L2RAM | SRAM /* Use the >> operator to indicate that an 
output section can be split, if necessary, into the specified memory 
ranges. */
    .far    >> L2RAM | SRAM    /* The .far section reserves space for 
global and static variables that are declared far. */
    .cinit    > SRAM    /* The .cinit section contains tables for 
initializing variables and constants. I believe that this is only the 
values that are used to initialize things at startup, and so are not 
needed during runtime. */
    .const    > SRAM    /* The .const section contains string literals, 
floating-point constants, and data defined with the C/C++ qualifier 
const (provided the constant is not also defined as volatile). */
    .pinit    > SRAM    /* Table of Global Object Constructors.  See 
below for full description */
}

/* .pinit Description: Global C++ variables having constructors and 
destructors require their constructors to be called during program 
initialization and their destructors  to be called during program 
termination. The C/C++ compiler produces a table of constructors to be 
called at startup. The table is contained in a named section called 
.pinit. The constructors are invoked in the order that they occur in the 
table. Global constructors are called after initialization of other 
global variables and before main( ) is called. Global destructors are 
invoked during exit( ), similar to functions registered through atexit( 
). */

chekib nouira wrote:
> be carefull of getting into cache coherency problems!!! you might get random data in L2!
>
> Chekib
> ----- Message d'origine ----
> De : "s...@hotmail.com" <s...@hotmail.com>
> À : c...@yahoogroups.com
> Envoyé le : Mercredi, 12 Mars 2008, 22h35mn 16s
> Objet : [c6x] Ext Memory access without EDMA
>
>                               Hi everyone,
>  
>  Is it possible to access external memory without using EDMA. I would like to pass a
buffer pointer located in external memory to a function call without configuring EDMA. The DSP
i am using is C6713. I would configure whole L2 as SRAM (256K) i.e., no L2 cache.
>  
>  Any comment will be appreciated.
>  
>  Thanks
>  
>  Sankar Barua
>  
>
>   
Check Out Industry's First Single-Chip, Multi-Format, Real-Time HD Video Transcoding Solution
for Commercial & Consumer End Equipment: www.ti.com/dm6467

(You need to be a member of c6x -- send a blank email to c6x-subscribe@yahoogroups.com )

Of course it is possible, it will just be a lot slower...around 10 times!

(You need to be a member of c6x -- send a blank email to c6x-subscribe@yahoogroups.com )

Thank you folks for reply. I am not using L2 Cache for two reasons:

1. I will be running shortage of RAM.
2. Most importantly, i am reading a block of data from Ext RAM only once. I read them into
internal memory and process it from internal memory. At that point i don't care about the  data
in Ext memory.

I keep hearing that i will lose speed if i don't use cache. My rational is that as  long as i
read the data only once it does not matter wheather you use cache or not speed will be  the
same. If you refer the same data more than once  then cache hit helps to speed up. Am I right.
Please comments:

Sankar

be carefull of getting into cache coherency problems!!! you might get rando=
>m data in L2!
>
>Chekib
>----- Message d'origine ----
>De : "s...@hotmail.com"   
>=C3=80 : c...@yahoogroups.com
>Envoy=C3=A9 le : Mercredi, 12 Mars 2008, 22h35mn 16s
>Objet : [c6x] Ext Memory access without EDMA
>
>                              Hi everyone,
>=20
> Is it possible to access external memory without using EDMA. I would like =
>to pass a buffer pointer located in external memory to a function call with=
>out configuring EDMA. The DSP i am using is C6713. I would configure whole =
>L2 as SRAM (256K) i.e., no L2 cache.
>=20
> Any comment will be appreciated.
>=20
> Thanks
>=20
> Sankar Barua
>=20
>Check Out Industry's First Single-Chip, Multi-Format, Real-Time HD Video Tr=
>anscoding Solution for Commercial & Consumer End Equipment: www.ti.com/dm64=
>67
>
>=20
>

------------------------------------

Check Out Industry's First Single-Chip, Multi-Format, Real-Time HD Video Transcoding Solution
for Commercial & Consumer End Equipment: www.ti.com/dm6467

(You need to be a member of c6x -- send a blank email to c6x-subscribe@yahoogroups.com )

Sankar,

On Thu, Mar 13, 2008 at 12:57 PM,  <s...@hotmail.com> wrote:

> Thank you folks for reply. I am not using L2 Cache for two reasons:
>
>  1. I will be running shortage of RAM.
>  2. Most importantly, i am reading a block of data from Ext RAM only once. I
> read them into internal memory and process it from internal memory. At that
> point i don't care about the data in Ext memory.
>
>  I keep hearing that i will lose speed if i don't use cache.
There is not a single answer to "should I use cache". One needs to
understand the application, DSP, and the DMA/cache/memory subsystem to
make the best decision.  Sometimes experiments are required.  Many
[most??] uses of DSPs involve a number of loops/iterations that get
significant performance gains from using cache.  It is not always the
answer.

> My rational is
> that as long as i read the data only once it does not matter wheather you
> use cache or not speed will be the same. If you refer the same data more
> than once then cache hit helps to speed up. Am I right. Please comments:
You are correct. "Single access stuff" gains no benefit from using cache.

mikedunn
>
>  Sankar
>
>  be carefull of getting into cache coherency problems!!! you might get
> rando=
>
>  >m data in L2!
>  >
>  >Chekib
>  >----- Message d'origine ----
>  >De : "s...@hotmail.com"
>  >=C3=80 : c...@yahoogroups.com
>  >Envoy=C3=A9 le : Mercredi, 12 Mars 2008, 22h35mn 16s
>
>  >Objet : [c6x] Ext Memory access without EDMA
>  >
>  > Hi everyone,
>  >=20
>
>  > Is it possible to access external memory without using EDMA. I would like
> =
>  >to pass a buffer pointer located in external memory to a function call
> with=
>
>  >out configuring EDMA. The DSP i am using is C6713. I would configure whole
> =
>  >L2 as SRAM (256K) i.e., no L2 cache.
>  >=20
>
>  > Any comment will be appreciated.
>  >=20
>  > Thanks
>  >=20
>  > Sankar Barua
>  >=20
>  >Check Out Industry's First Single-Chip, Multi-Format, Real-Time HD Video
> Tr=
>  >anscoding Solution for Commercial & Consumer End Equipment:
> www.ti.com/dm64=
>  >67
>  >
>  >=20
>  >
>  

-- 
www.dsprelated.com/blogs-1/nf/Mike_Dunn.php

------------------------------------

Check Out Industry's First Single-Chip, Multi-Format, Real-Time HD Video Transcoding Solution
for Commercial & Consumer End Equipment: www.ti.com/dm6467

(You need to be a member of c6x -- send a blank email to c6x-subscribe@yahoogroups.com )