path: root/Documentation/xtensa/atomctl.txt
diff options
authorMax Filippov <>2012-11-19 07:00:41 +0400
committerChris Zankel <>2012-12-18 21:10:22 -0800
commitc622b29d1f38021411965b7e0170ab055551b257 (patch)
treef86875612ade331965b80abafb14cbd796924461 /Documentation/xtensa/atomctl.txt
parent733536b865441d9bad02c4711a4372d48ce21e54 (diff)
xtensa: initialize atomctl SR
In order to use S32C1I instruction on cores with ATOMCTL SR the register must be properly initialized. Signed-off-by: Max Filippov <> Signed-off-by: Chris Zankel <>
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+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
+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.
+ 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 of ISA; Bits:
+ 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 Exception Reserved
+ 3 Reserved Reserved Reserved