Lpc2000

--- In lpc2000@yahoogroups.com, "Joel Winarske" <joelw@i...> wrote:
>
> Sten wrote:
> >
> >Does anybody has some experiences in what data rate can be 
achieved when
> >writing to an SD/MMC card? What is the bottleneck (software/FAT 
or SPI)?
> 
> Based on the user manual:
> The minimum divider value on the SSP peripheral is 2.  You can run 
the
> peripheral clock at CPU speed; 1:1.  The SD Card Max clock speed 
for SPI
> mode is 25MHz.  So if you run the peripheral clock at 50MHz you can
> potentially access the SD card at the maximum SD SPI frequency.
> 
> Some FAT implementations use less RAM and more ROM, some feature 
caching and
> use quite a bit more RAM.  So depending on your requirements and 
budget you
> have some optimizing options.
> 
> 
> Joel
>

I had it written down but lost it...  I think I am moving about 
170,000 bytes per second using a Compact Flash (8 bit parallel mode) 
and an LPC2106.  No cache or buffering.  I have been thinking about 
read-ahead since my MP3 player will always play just one file and 
will always play it all the way through.

OTOH, I think I can shovel data at 10 times the rate required so why 
bother?  The Rogue Robotics uMP3 player uses SD and an Atmel 
ATmega128L so it is running at 8 MHz, using SPI and it can still 
keep up with the MP3 data rate of ABOUT 1 MB per minute. or 16kB per 
second.

My development board is in complete disarray at the moment or I 
would just rerun the timing tests.  But I think the 170kB is correct.

Richard