Programming advice for exclusive resource locking
ke4pjw
Posts: 1,155
I am looking for the best way to exclusively lock a hardware resource. My specific use case is a wiznet Ethernet chip. I know in the past on the P1, a single COG would be dedicated to communication with such a device and all information would pass through a command register in Hub RAM. All other resources would wait for the command register to clear. Since only one cog could access the Hub at a time, that worked fine for the P1. I am concerned that is not the case for the P2, as all cogs can access the hub at once. I need to be able to perform a mutex type operation. I was thinking that the locks (that I have never seen used in the wild on the P1) would be a good facility for this type of operation.
Your comments are appreciated.
Thanks,
Terry
Comments
To be clear, the cogs of the P2 cannot access the same address in hub RAM at the same time. Using a lock is probably the best way to go when you need to protect more than a single long. I only ever used locks once with the P1, and looking at the P2 docs they seem a little easier to use. I knocked together a quick demo to try them; maybe it will help. The key is acquiring a lock, then sharing the lock ID with the cogs that may need exclusive access to specific resources.
An adjacent cog can simultaneously access an adjacent hub address, or any multiple of eight offset from the adjacent address.
PS: Longword granular addresses that is.