Kinetis Microcontrollers中的主题 Re: K70 external ram simple question

K70 external ram simple question

James8 — Thu, 10 May 2012 15:55:01 GMT

Hi, I'm looking at using a K70 for a new project but having never used external ram in any embedded project before, I just have a simple question... once all the registers and what-not are set up, can the memory be used just like internal SRAM? i.e. completely transparently from the C code's point of view:

void foo(uint32_t * p)
{

*p = 0;
}

foo(sram_pointer);

foo(dram_pointer);

as oppose to say having to use some compiler extension like "unsigned int far *" or needing to use registers in order to actually read/write to the memory.

Are there any restrictions you think I might need to know about?

Thanks

Re: K70 external ram simple question

konrada — Thu, 10 May 2012 17:03:55 GMT

External RAM can be used like internal RAM; it lies in the same 32-bit flat address space. Things to look out for:

External RAM is slower => need to enable cache => need to flush/disable cache when dealing with DMA buffers
Debugger support is more adventurous. If your debugger and JTAG adapter work fine with internal RAM, that doesn't mean it will work fine with external RAM (e.g. can't read/write ext ram from debugger, can't put breakpoints on external RAM addresses). However, that's more a problem of immaturity of Kinetis tooling, and time is working for you.

Re: K70 external ram simple question

James8 — Thu, 10 May 2012 17:35:28 GMT

Cool, thanks.

I have a Jlink Ultra which at least claims to support external RAM, so I guess we'll see.