Where should I discuss SD/MMC FAT issues?

[JD123]

We'll, I've done my best and yes, about 84K Tcy is as fast as this thing is going to read 512 bytes from the MMC and write the 512 bytes to the FRAM. It's 83,968 Tcy to be exact. Last night I thought I'd give it one more go.

At the start of the evening I got my latest code loaded and checked for timer1 overflows. Yep, it was running over. The true transfer times were 166,837 Tcy. I started dissecting the code bit by bit and embedding timers to catch cycle times. Turns out I had a very inefficient MMC routine. I strait-lined the code and got it back up to speed. I tweaked the I2C as well as moving the two function subs WRITE_I2C and GET_BYTE to the top of the program. Within an hour or two I got it down to 129,837 Tcy. After doing some math, I figured I was eating 45 Tcy with every loop and couldn't account for where it was coming from. The last part of the routine to be counted was the time needed to simply perform the FOR-NEXT loop.

Bingo! Turns out using WORD sized variables in a FOR-NEXT loop can be a huge Tcy eater. The solution I used was to break up the 512 count in the for-next loop to two 256 count loops. Boom! The cycle times fell to 83,986 Tcy. So, in a few hours, I saved 82,869 Tcy, saved 400 lines of complied code and gained about twice the speeds. I'm currently at 16mhz ripping the MMC sector and writing it in a total of just under 21ms. Still not fast enough to use it as I would like, but still... that's fast I2C.

Here's the updated code: