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Honored Contributor
Honored ContributorSRAM vs SDRAM
Hi,
I am about to design a system with uClinux, and I was wondering if the performances would be correct if I only used an SDRAM. SRAM is a bit expensive if I want to have enough memory to run my linux (I guess I need at least 4MB). However, I have read in some threads around here that SDRAM performances were quite bad. Is there any experience here of people running linux without SRAM ? My second question is quite the same and about the Altera Cyclone devboard : I use the standard design (using SRAM as exception address thus), and I follow the Quick Start Guide to build a kernel, that I run from the SDRAM. In this case, I suppose the whole kernel is uploaded in SDRAM and then executed from there. My question is : is the SRAM still in use ? Do I lose any performance if I remove it ? I can see that ramfs file systems are mounted but I guess its only in SDRAM. I suppose the /dev/ramX are linked to the SDRAM, not the SRAM, so is the SRAM in use ? Thanks a lot cetic17 Replies
Altera_ForumHi cetic,
> ... I have read in some threads around here that SDRAM performances > were quite bad. I've found the SDRAM controller performance to be pretty awful. Given the logic area it occupies and its performance, I no longer consider it a viable alternative for many new designs. > SRAM is a bit expensive if I want to have enough memory to run > my linux (I guess I need at least 4MB). I've switched to PSRAM (pseudo SRAM) for new designs. It eliminates the SDRAM controller and it performs better. The cost is very attractive ... the expense is the number of pins you must use. Regards, --Scott- Altera_Forum
Thanks for your reply,
that means that the system I am currently using on the Altera Cyclone devboard is very slow, I guess. Do you still have an idea whether the SRAM is used or not ? My question is do I still need a SRAM if I made a custom board where Linux is run from a SDRAM (just like on the devboard) ? Any way I will check the PSRAM solution. Thanks, cetic - Altera_Forum
> Do you still have an idea whether the SRAM is used or not ?
I don't believe it's used in the kernel version I'm using. It might be mapped in mtd ... I never checked ... and I didn't see it mapped into a region in the startup either. > do I still need a SRAM if I made a custom board where Linux is > run from a SDRAM (just like on the devboard) ? No, the SRAM is not necessary -- you can run linux just fine without it. Regards, --Scott - Altera_Forum
Dear Scott,
may I ask you what PSRAM you use (manufacturer) and what amount of memory I need to run a linux properly ? Thanks a lot cetic - Altera_Forum
Hi cetic,
I'm using Micron MT45W4MW16PFA (4M x 16-bit), but will be switching to the MT45W2MW16PFA (2M x 16-bit) if all goes well. The marketing name for the part family is "ASYNCHRONOUS CellularRAM". > what amount of memory I need to run a linux properly ? That depends on your application's memory requirements. For my application 8 MB is plenty, but 4 MB might be a tad too tight. The two parts above are pin compatible ... so I'm not terribly concerned. You might want to do some experimenting on a development board (altera or microtronix) ... to get a better feel for your requirements. Regards, --Scott - Altera_Forum
Thanks a lot
cetic - Altera_Forum
Have you considered using mainstream DDR RAM instead of SDRAM?
Altera's DDR RAM controller offers better performance than our SDRAM controller. - Altera_Forum
Can anyone provide any form of performance data using DDR SRAM and nios2?
Marco would you mind providing some insight? - Altera_Forum--- Quote Start --- originally posted by smcnutt@Jan 20 2005, 07:29 PM hi cetic,
> ... i have read in some threads around here that sdram performances
> were quite bad.
i've found the sdram controller performance to be pretty awful. given
the logic area it occupies and its performance, i no longer consider it a
viable alternative for many new designs.
> sram is a bit expensive if i want to have enough memory to run
> my linux (i guess i need at least 4mb).
i've switched to psram (pseudo sram) for new designs. it eliminates
the sdram controller and it performs better[/b]. The cost is very attractive ... the expense is the number of pins you must use. Regards, --Scott <div align='right'><{post_snapback}> (index.php?act=findpost&pid=4142) --- Quote End --- [/b] --- Quote End --- <div class='quotetop'>QUOTE </div> --- Quote Start --- I've found the SDRAM controller performance to be pretty awful. Given the logic area it occupies and its performance, I no longer consider it a viable alternative for many new designs.[/b] --- Quote End --- Is these tru, If so, how much slower will it be. Frequeny
- Altera_Forum--- Quote Start --- originally posted by smcnutt@Feb 3 2005, 02:33 PM i'm using micron mt45w4mw16pfa (4m x 16-bit), but will be
switching to the mt45w2mw16pfa (2m x 16-bit) if all goes well.
<div align='right'><{post_snapback}> (index.php?act=findpost&pid=4494)
--- quote end ---
--- Quote End --- What is the difference in prize of this memory compared to sdram ? half ? twice ? Regards. Michael Schmitt
