[Tinyos-Storage WG] Meeting minutes 04/20

[Gaurav Mathur]

+ Discussion of David's TEP drafts

 - Good starting point for the TEP.
 - We weren't sure about the minimum volume size specified by the  
TEP. David mentioned that the implementation enforces minimum volume  
size to be 1 erase block. David thought 2 would be needed for  
rollaround reasons. For read-only small objects, 2 seems overkill


+ TEP 129 (Platform Independent Non-Volatile Storage Layers)

 - Gaurav/Deepak will take lock on TEP draft and add some more layers  
from our Capsule implementation
 - If others have more objects to add to what we already have, that  
would be great.

+ Checkpointing and rollback

 - Existing storage objects implement checkpointing/rollback  
individually.
 - No generic framework for checkpointing/rollback across different  
objects.

 - We thought that it would be good to get a draft TEP of this  
component before TTX. David and Gaurav to share their checkpoint -  
rollback implementations and try and come up with interfaces, etc.  
that could be used to provide checkpoint and rollback to objects/ 
application. Others are welcome to contribute and share the load.

 - One question that was discussed is whether the implementations use  
only the flash or should they use the internal EEPROM when available.  
We thought it would be best to use a "checkpointing volume" in flash  
since EEPROM specs can vary widely and some processors don't have  
them at all.


+ Sharing of objects on flash

 - Tricky, not clear at this point how to go about doing this. Some  
of the issues involved are :
	a) the objects manage their own volume (perform their own reads/ 
writes/erases) and its unclear how multiple objects can co-manage  
each volume
	b) garbage collecting within a volume shared by multiple objects is  
complicated and code/memory-intensive
	c) the concept of sharing the volume breaks the volume abstraction  
whose purpose is to partition the flash among different objects

 - We thought it best to push this discussion to the TTX or after  
that and focus on the the rest until TTX.


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