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List:       uclinux-dev
Subject:    Re: [uClinux-dev] External memory layout
From:       Erwin Authried <eauth () softsys ! co ! at>
Date:       2007-06-28 14:12:23
Message-ID: 1183039943.22460.385.camel () justakiss ! home ! at
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Am Donnerstag, den 28.06.2007, 15:43 +0200 schrieb Daniel Chicco:
> Hi All,
>  
> First, sorry for my poor English writing skills.
> I īm new in uClinux and I īm designing a CPU board with an ARM processor
> (NXP LPC2468 for more details) to run uClinux. 
> I īm chossing the memory layout for external memories and initially I
> selected an SDRAM memory to run uClinux kernel code and a serial flash
> to store kernel (that is copied to SDRAM at boot), applications and
> data (1 MB of data aproximatelly). Is this schema a good choice to run
> uClinux?
this is a good choice, if your SDRAM is big enough to hold kernel +
apps.

> Another doubt is what are the tradeoffs of choose between an external
> memory data bus of 16 bit wide and 32 bits wide?, independently of
> memory prices of course.
>  

If you use the 32-bit ARM mode with 16-bit memory, the cpu needs two
memory cycles for each instruction fetch. This will make your system
slower, 50% in worst case. It is quite usual to use 16-bit only, many
ARM7TDMI cpus have a 16-bit external interface only.

Regards,
Erwin

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