DDR SDRAM vs SSRAM

Hi mendonca,

just a guess: the nios/f has data cache.

If another avalon master changes the value of your flag in memory, the nios/f processor doesn't notice, because it loads the value from the cache. If you load the values by using the 'ldwio' opcode, you read the value directly from memory.

And depending on your optimization level, the value isn't read at all from memory, only a value in a processor register is checked. You can cirumvent this by adding 'volatile' to your variable declaration.

Also, isn't there a hardware mutex component that synchorinzes access to memory between different processors?

Wolfgang

while(shared_memory->flag =! OK); (***)

mendonca,

are you shure:

You want to load 'shared_memory->flag' with the inverted value of 'OK' and then check if this is not zero? Or do you want to wait until the flag is '!OK'?

If so you have to write:

while(shared_memory->flag != OK);

Mike

Hi, Wolfang.

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originally posted by wpaulus@Aug 17 2006, 07:03 AM

just a guess: the nios/f has data cache.

if another avalon master changes the value of your flag in memory, the nios/f processor doesn't notice, because it loads the value from the cache.

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Good point! I&#39;ve thought that declaring my on-chip memories instances as volatile, this problem couldn&#39;t happen. However, the problem is still deeper. I had already also tried to run the application under Nios/f processor without data cache (0Kb). The problem remained.

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originally posted by wpaulus@Aug 17 2006, 07:03 AM

if you load the values by using the &#39;ldwio&#39; opcode, you read the value directly from memory.

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I&#39;ve enjoyed your suggestion too much. Can you send me a simple example of how can I use that opcode. I don&#39;t know it yet. Or, maybe, the name of the header file where are declaring the routines I need to use. With this I suppose I can take more informations in Nios II Software Handbook.

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originally posted by wpaulus@Aug 17 2006, 07:03 AM

and depending on your optimization level, the value isn&#39;t read at all from memory, only a value in a processor register is checked. you can cirumvent this by adding &#39;volatile&#39; to your variable declaration.

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I&#39;ve checked my code again and, in fact, I used &#39;volatile&#39; in all the declaration of the 4 shared memories.

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originally posted by wpaulus@Aug 17 2006, 07:03 AM

also, isn&#39;t there a hardware mutex component that synchorinzes access to memory between different processors?

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Yes. Actually, each memory has a mutex protecting it.

This question remembers me another doubt. What, in fact, happens when a processor try to verify the value of a variable, like in (***)? I&#39;ve noticed, at least in my projects, that checking this before or after lock a mutex makes no difference. Is there no conflit among processor when trying to verify memory on this way?

Thank you to much, Wolfang. We had a good discussion here.

I&#39;ll be waiting new suggestions from Nios Community.

Regards,

Mendonça.

Hi mendonca,

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originally posted by mendonca@Aug 17 2006, 08:56 AM

i&#39;ve enjoyed your suggestion too much. can you send me a simple example of how can i use that opcode. i don&#39;t know it yet. or, maybe, the name of the header file where are declaring the routines i need to use. with this i suppose i can take more informations in nios ii software handbook.

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In the Nios II Software Developer&#39;s Handbook look at Chapter 7 Cache & Tightly-Coupled Memory. There is a section about Managing Cache in Multi-Master Systems. Cache bypassing is explained there.

Just another heretic thought: Have you connected your on-chip memory to all of your processors in sopc builder? If they aren&#39;t connected and you read from the address you get undefined results, maybe 0x00 or 0xff.

while(shared_memory->flag != OK); (***)
lock_mutex;
read_and_write_data;
unlock_mutex;

btw, why do you check the flag before taking the (hardware) semaphore? The purpose of the semaphore is to synchronize access to shared memory. Why not use the api provided by Altera for the semaphore and leave the work to their code?

Regards,

Wolfgang