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1 We Have Atomic Operation Control (ATOMCTL) Register.
2 This register determines the effect of using a S32C1I instruction
3 with various combinations of:
4
5 1. With and without an Coherent Cache Controller which
6 can do Atomic Transactions to the memory internally.
7
8 2. With and without An Intelligent Memory Controller which
9 can do Atomic Transactions itself.
10
11 The Core comes up with a default value of for the three types of cache ops:
12
13 0x28: (WB: Internal, WT: Internal, BY:Exception)
14
15 On the FPGA Cards we typically simulate an Intelligent Memory controller
16 which can implement RCW transactions. For FPGA cards with an External
17 Memory controller we let it to the atomic operations internally while
18 doing a Cached (WB) transaction and use the Memory RCW for un-cached
19 operations.
20
21 For systems without an coherent cache controller, non-MX, we always
22 use the memory controllers RCW, thought non-MX controlers likely
23 support the Internal Operation.
24
25 CUSTOMER-WARNING:
26 Virtually all customers buy their memory controllers from vendors that
27 don't support atomic RCW memory transactions and will likely want to
28 configure this register to not use RCW.
29
30 Developers might find using RCW in Bypass mode convenient when testing
31 with the cache being bypassed; for example studying cache alias problems.
32
33 See Section 4.3.12.4 of ISA; Bits:
34
35 WB WT BY
36 5 4 | 3 2 | 1 0
37 2 Bit
38 Field
39 Values WB - Write Back WT - Write Thru BY - Bypass
40 --------- --------------- ----------------- ----------------
41 0 Exception Exception Exception
42 1 RCW Transaction RCW Transaction RCW Transaction
43 2 Internal Operation Internal Operation Reserved
44 3 Reserved Reserved Reserved