GR740-UM-DS, Nov 2017, Version 1.7
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GR740
6.9.3
ASI 0x2, System control registers
ASI 2 contains a few control registers that have not been assigned as ancillary state registers. These
should only be read and written using 32-bit LDA/STA instructions.
All cache registers are accessed through load/store operations to the alternate address space (LDA/
STA), using ASI = 2. The table below shows the register addresses:
6.9.4
ASI 0x8-0xB, Data/Instruction
These ASIs are assigned by the SPARC standard for normal data and instruction fetches.
Accessing the instruction ASIs explicitly via LDA/STA instructions is not supported in the LEON4
implementation. Using LDA/STA with the user/supervisor data ASI will behave as the affect the
HPROT signal emitted by the processor according to section 6.7.1, but MMU access control will still
be done according to the super-user state of the %psr register.
6.9.5
ASI 0xC-0xF, ICache tags/data, DCache tags/data
ASI 0xC-0xF provide diagnostic access to the instruction cache memories. These ASIs should only be
accessed by 32-bit LDA/STA instructions. These ASIs can not be used while a cache flush is in prog-
ress.
The same address bits used normally as index are used to index the cache also in the diagnostic
access. For a multi-way cache, the lowest bits above the index part, the lowest bits that would nor-
mally be used as tag, are used to select which way to read/write. The remaining address bits are don’t
cares, leading the address map to wrap around.
The tag parity and context bits can also be read out through these ASIs by setting the PS bit in the
cache configuration register. When this bit is set, the parity data is read instead of the ordinary data.
When writing the tag bits, the context bits will always be written with the current context in the MMU
control register. The parity to be written is calculated based on the supply write-value and the context
ID in the MMU control register. The parity bits can be modified via the TB field in the cache control
register.
Table 44.
ASI 2 (system registers) address map
Address
Register
0x00
Cache control register
0x04
Reserved
0x08
Instruction cache configuration register
0x0C
Data cache configuration register