After tweaking, I was able to get the SD performance up to 750kB/s. This was accomplished by reducing the number of commands I sent to the card, as well as upping the clock rate. I also turned off INVARIANTS and WITNESS. Here's the numbers at each step: baseline: 200kB/s. Double clock rate: 220kB/s. Remove INVARIANTS and WITNESS: 340kB/s. Remove STOP and useless select commands: 750kB/s. I think could squeeze a little more out by tightening up the code, but not more than 1 or 2kB/s.
I think I can further improve the performance to the card by in 4-bit mode. Doing multiblock reads would also help. Maybe switching from a MPSAFE interrupt to a FAST interrupt routine would improve things as well. Hard to say for sure.
However, before doing more performance tweaking, I need to make all the error paths robust in the fact of actual errors. I also need to deal with proper timeouts.
I am guessing that the 750k is read.
ReplyDeleteCan you break down the performance into read and write?
In other words what is your sustained write rate vs what is your sustained read rate for something like a 16mb
file.