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5f42146e75
Make the WT entry match table 4-52 of the Xtensa ISA RM (RD-2012.5). Signed-off-by: Baruch Siach <baruch@tkos.co.il> Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
45 lines
1.9 KiB
Plaintext
45 lines
1.9 KiB
Plaintext
We Have Atomic Operation Control (ATOMCTL) Register.
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This register determines the effect of using a S32C1I instruction
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with various combinations of:
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1. With and without an Coherent Cache Controller which
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can do Atomic Transactions to the memory internally.
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2. With and without An Intelligent Memory Controller which
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can do Atomic Transactions itself.
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The Core comes up with a default value of for the three types of cache ops:
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0x28: (WB: Internal, WT: Internal, BY:Exception)
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On the FPGA Cards we typically simulate an Intelligent Memory controller
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which can implement RCW transactions. For FPGA cards with an External
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Memory controller we let it to the atomic operations internally while
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doing a Cached (WB) transaction and use the Memory RCW for un-cached
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operations.
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For systems without an coherent cache controller, non-MX, we always
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use the memory controllers RCW, thought non-MX controlers likely
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support the Internal Operation.
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CUSTOMER-WARNING:
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Virtually all customers buy their memory controllers from vendors that
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don't support atomic RCW memory transactions and will likely want to
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configure this register to not use RCW.
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Developers might find using RCW in Bypass mode convenient when testing
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with the cache being bypassed; for example studying cache alias problems.
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See Section 4.3.12.4 of ISA; Bits:
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WB WT BY
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5 4 | 3 2 | 1 0
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2 Bit
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Field
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Values WB - Write Back WT - Write Thru BY - Bypass
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--------- --------------- ----------------- ----------------
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0 Exception Exception Exception
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1 RCW Transaction RCW Transaction RCW Transaction
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2 Internal Operation Internal Operation Reserved
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3 Reserved Reserved Reserved
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