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| -rw-r--r-- | Documentation/xtensa/atomctl.txt | 44 |
1 files changed, 44 insertions, 0 deletions
diff --git a/Documentation/xtensa/atomctl.txt b/Documentation/xtensa/atomctl.txt new file mode 100644 index 000000000..1da783ac2 --- /dev/null +++ b/Documentation/xtensa/atomctl.txt @@ -0,0 +1,44 @@ +We Have Atomic Operation Control (ATOMCTL) Register. +This register determines the effect of using a S32C1I instruction +with various combinations of: + + 1. With and without an Coherent Cache Controller which + can do Atomic Transactions to the memory internally. + + 2. With and without An Intelligent Memory Controller which + can do Atomic Transactions itself. + +The Core comes up with a default value of for the three types of cache ops: + + 0x28: (WB: Internal, WT: Internal, BY:Exception) + +On the FPGA Cards we typically simulate an Intelligent Memory controller +which can implement RCW transactions. For FPGA cards with an External +Memory controller we let it to the atomic operations internally while +doing a Cached (WB) transaction and use the Memory RCW for un-cached +operations. + +For systems without an coherent cache controller, non-MX, we always +use the memory controllers RCW, thought non-MX controlers likely +support the Internal Operation. + +CUSTOMER-WARNING: + Virtually all customers buy their memory controllers from vendors that + don't support atomic RCW memory transactions and will likely want to + configure this register to not use RCW. + +Developers might find using RCW in Bypass mode convenient when testing +with the cache being bypassed; for example studying cache alias problems. + +See Section 4.3.12.4 of ISA; Bits: + + WB WT BY + 5 4 | 3 2 | 1 0 + 2 Bit + Field + Values WB - Write Back WT - Write Thru BY - Bypass +--------- --------------- ----------------- ---------------- + 0 Exception Exception Exception + 1 RCW Transaction RCW Transaction RCW Transaction + 2 Internal Operation Internal Operation Reserved + 3 Reserved Reserved Reserved |