alt_read_flash too slow?

Maybe something is doing a sector erase - 500ms would be about right for that.

I looked at the low level flash functions a few weeks ago, IMHO you want to use the lower level functions (about two levels down) so that you can write partial blocks (ok if the old data if 0xff - or rather if the write doesn't need to set any bits).

Might be worth adding some trace to thiose to see what is taking all the time.

Also see if a read of 128k actually takes 1/2 the time - ie is it a per byte cost or a fixed overhead.