If I'm not mistaken, SDcards have some intelligence integrated that will balance this. So, even if you write always to the same address, the card will re-map this to a different physical sector of the memory.
This is true, however it remaps it to a small reserved section of memory that's not part of the main accessible memory. It doesn't really solve my "problem" because in cases where sectors start dying because I've got overdub on all the time, it would be whole huge sections, way more than the few Mb's that are in reserve on the sd card.
However... all this made me have an idea! It might be that it was already suggested in the thread and I didn't get it at the time over a year ago, or not, I cant remember, but now I think it's the best bet.
Memory would be separated into two kinds of chips:
-Small capacity SRAM but with unlimited endurance, like the MR25H40
-Large capacity flash with limited endurance, like 64Mb microchip flash, 100,000 rewrites, or better, micron phase change memory, 128Mb, 1,000,000 rewrites
Whenever in record/overdub/write modes, I'd have the looper decide which memory chip to use. If the loop (or cropped section of loop) is being recorded/overdubbed, I'd use the small capacity SRAM with unlimited endurance, such as the MR25H40 I've been trying out, 4Mb, good for a little over 5 seconds of audio at 16bit 48khz. I can do a million overdubs on that small bit of memory without issues. If I "uncrop" the loop, extend the loop (or just re-record a larger loop), greater than 5 seconds, I'll have the looper seamlessly shift the data into the limited endurance high-capacity flash memory, all in the background. It would take months of continuous overdubbing if my loop is over 5 seconds long to burn through flash memory, so no real issue.
The real challenge is having the looper switch between the two types of memory based on whatever amount of audio is "active" at any given moment, then moving to the different memory without interupting audio.