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P/V Synchronized and Try Views can be used to access Semaphore cells.
Load returns current value and post-decrements the value in the cell
(until it reaches zero). Stores increment the value (until it saturates
at 0xFFFF).
P/V Synchronized View causes the issuing thread to block on read if value
is 0. P/V Try View does not block the thread, it returns 0 in this case.
Cell's Empty and Full bits are not modified.
Trap bit (i.e. Gating Storage exceptions) not implemented.
Signed-off-by: Leon Alrae <leon.alrae@imgtec.com>
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Empty/Full Synchronized and Try views can be used to access FIFO cells.
Store to the FIFO cell pushes the value into the queue, load pops the oldest
element from the queue. Cell's Full and Empty bits are automatically updated
to reflect new state of the cell.
Empty/Full Synchronized View causes the issuing thread to block when FIFO is
empty while thread is performing a read, or FIFO is full while thread is
performing a write.
Empty/Full Try View never blocks the thread. If cell is full then write is
ignored, if cell is empty then load returns 0.
Trap bit (i.e. Gating Storage exceptions) not implemented.
Store Conditional support for E/F Try View (i.e. indicate failure if FIFO
is full) not implemented.
Signed-off-by: Leon Alrae <leon.alrae@imgtec.com>
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Control view is used to access the ITC Storage Cell Tags. It never causes
the issuing thread to block.
Guest can empty the FIFO cell by setting Empty bit to 1.
Signed-off-by: Leon Alrae <leon.alrae@imgtec.com>
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Implement ITC as a single object consisting of two memory regions:
1) tag_io: ITC Configuration Tags (i.e. ITCAddressMap{0,1} registers) which
are accessible by the CPU via CACHE instruction. Also adding
MemoryRegion *itc_tag to the CPUMIPSState so that CACHE instruction will
dispatch reads/writes directly.
2) storage_io: memory-mapped ITC Storage whose address space is configurable
(i.e. enabled/remapped/resized) by writing to ITCAddressMap{0,1} registers.
ITC Storage contains FIFO and Semaphore cells. Read-only FIFO bit in the
ITC cell tag indicates the type of the cell. If the ITC Storage contains
both types of cells then FIFOs are located before Semaphores.
Since issuing thread can get blocked on the access to a cell (in E/F
Synchronized and P/V Synchronized Views) each cell has a bitmap to track
which threads are currently blocked.
Signed-off-by: Leon Alrae <leon.alrae@imgtec.com>
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