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Throughput USB/SDCARD on DRM104 DEMOFLEXISJMSD MC9S08JM60

Question asked by James Murray on Feb 15, 2013
Latest reply on Mar 4, 2013 by Monica Arvizu

I have been evaluating the JM60 part using the DEMOFLEXISJMSD board. I watched the webcast which is a good introduction.

 

I was able to load the card reader and terminal software without trouble and they work exactly as described. So far so good.

 

However, the read rate on the SDcard reader application is very poor.

 

I created a random 10 meg file on the card and for simplicity I'm using dd to read it back (under Linux, same speed under Cygwin.)

 

$ dd if=/media/USB\ COPIER/10meg1 of=/dev/null bs=512

20480+0 records in

20480+0 records out

10485760 bytes (10 MB) copied, 76.5 s, 137 kB/s

 

 

With a cheap, nasty and old off the shelf reader I can get 8.0M/s so that's a huge difference.

 

I made some quick wins in speed by flattening the code to eliminate function calls and then bypassed the EP1_Load() step to write directly to USB RAM. (I've not yet used the double buffers of EP5/6.)

 

This now yields 251 kB/s, but that's still a mile away from my target and suggests I should switch to a different part or vendor.

 

Am I asking too much of this MCU ? or does someone have example code that gives a useful performance ?

 

regards

 

James Murray

 

PS. This new forum layout feels harder to use.

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