Re: DMA during Standby Mode on the AT91RM9200?

Oh I see, you are working at Atmel? Great, then I've someone found who
knows what he is talking about.
The AT91RM9200 seems to be a very low power device so it is not really
necessary to drive the processor an the lowest power mode that is
possible. Even if the processor is running in "normal" mode 24.4mA +
some current required by the peripherals seems to be absolute
sufficient to meet our requirements. But anyway, we could even reach
better power consumption values if running the PLL in slower mode, your
mentioned 25MHz (MCK).
Do you have some typical power consumption values for VDDIO?


But what about memory? It seems to be strange that for each chip select
a 256MB space is reserved but only 64MB can be addressed.
Does this limitation also concern the SDRAM memory? We need lots of
memory, it remains to be seen if it is really required by the
application but at least the customer insists on 128MB to 256MB. But if
we have the same limitation as with the static memory controller we
come into troubles. The data*** mentions a page size range up to 8192
rows, 2048 columns, 4 banks and 32bit data. Mathematical it is possible
to address 256MB, but pracital?
If the AT91RM9200 have the 64MB limitation for SDRAM, then we fancy
with the AT91SAM9261 as it supports a LCD controller, desired by our
customer as well. Does it have the same limitation?

Thanks for your great help.

Regards,
Thomas


Ulf Samuelsson schrieb:

I want to build a system that supports a very low power mode. For this
purpose I will use the AT91RM9200 as it seems to be very useful for
this application. To meet the power requirements the mentioned
processor needs to be either in standby or slow clock mode.

I think you probably need to have the PLL running to receive the Ethernet
frames.
Typically you need 2-4 x speed to receive a clock
MII is 25 Mhz and RMII is 50 Mhz, so you need some speed there.
The CPU can of course be turned off, but you are talking mA and not uA
still.
PLL in itself needs some mA.

As I've read in the data*** the processor can be awaken by an
external interrupt (e.g. pressing a push button) but what about
reception of a frame via the ethernet interface?

Is it possible to enable a DMA transfer from the ethernet MAC to the 16k
internal memory?

Yes.

Is this DMA channel working even if the processor is in standby?

Yes, if the peripheral clock is enabled

If the packet, and just if, is addressed to the processor it should awaken
and
process the data transferred via the DMA.

I think that if the packet is addressed elsewhere, the packet will be
filtered away and no interrupt occurs.

--
Best Regards,
Ulf Samuelsson
This is intended to be my personal opinion which may,
or may bot be shared by my employer Atmel Nordic AB

.