FASTER I2C external EEPROM writing library!

[Marttyn]

Hi!
Ive been working on a project that needs to write to an external EEPROM, and then continue doing "stuff" very quickly. The problem for me was not the time from write to write (usually 5ms). My program writes every 20ms.
My problem was to wait 5ms after the I2C data was sent to the EEPROM.

The key point is that once you send the data, the EEPROM "writes itself alone", you can stay there or you can be doing other things... so I preferred to do other things instead of waiting :D

With this in mind I improved libraries for 256K and 1024K (the ones i use the most). Also implemented page read and write, and a function to show over serial whats inside the EEPROM with a nice format (thanks to http://www.ccsinfo.com/forum/viewtopic.php?t=58490 for helping find to "compile or not").

What i did to improve speed? Instead of waiting AFTER writing, my library waits BEFORE writing... Wait, what!?
Usually EEPROM libraries write, and then polls to the EEPROM for the finish.
While my approach simply writes, and then exit, without polling.
Instead the read and write functions check if the EEPROM is ready before sending a new read/write command. If the EEPROM is still writing from previous operations, then wait until finish, and then continue.

This way, the time for a single write operation is very fast:
Enter function -> Check if EEPROM is busy -> Write -> Exit
No waiting at all! This save us 3-5ms of waiting.

While consecutive writings will still needs to wait for the previous operation to finish.

I did some research, and this technique is not commented anywhere. Although Microchip has an application note about how to use EEPROMs and how to improve speed: http://ww1.microchip.com/downloads/en/Appnotes/01028B.pdf

To be honest, as no one used this approach, and further Microchip don't talk about this anywhere, I've thought that this would not work. But after many test, this seems to work consistently, and I'm using it on a production product.

This are some test made at 400Khz bus speed with PIC hardware I2C and 32Mhz internal oscillator, using a 24AA1025 memory: