[Yaffs] Garbage Collection

Hi,

I wonder how yaffs select those block that need to be erased when perform gc. For example when the block state is full, and there are only few pages that is invalid, will yaffs erased that block? In ohter words, when the invlid pages is more than a specific value , this block is taken to be erased when gc. Moreover, i want to know when the yaffs start the passive and aggressive gc, every start time or just perform the gc when the flash left block number is smaller than the reserved block number. Thank you.

Alex