Model 466-1 Adapter
54 CSR Accessed From The SBus
LOCK BUS (bit 4): Writing a "1" to bit 4 sets the Lock Bus flip-flop. If the
Lock Bus flip-flop is set, the address strobe signal on the VMEbus remains
active after the first SBus access to the VMEbus. This prevents any other
VMEbus bus master from using the bus and permits the SBus to convert a
read operation followed by a write operation into an atomic read-modify-write
on the VMEbus.
To use the Lock Bus function, the SPARCstation user should set the Lock Bus
flip-flop, then perform a read followed by a write (to the same address on the
VMEbus). Then, quickly clear the Lock Bus flip-flop.
The Lock Bus function is useful in multi-processor applications where
processors often signal availability of a resource through an indivisible
read-modify-write semaphore operation. The Lock Bus flip-flop may also be
used by the SBus to make accesses to Dual Port RAM indivisible.
Read-modify-write operations (such as TAS: test and set) from the VMEbus to
Dual Port RAM are automatically indivisible.
The
Lock Bus
bit is used only for read-modify-write operations. Any
other use is not supported.
USE ADDRESS PAGE REGISTER (bit 3): The SBus may address remote
RAM or Dual Port RAM using Direct Mode or Page Mode. In Direct Mode,
memory is addressed by setting a window in SBus slot I/O address space as
large as the block of VMEbus RAM. In Page Mode, memory is addressed
through a smaller window than the block of RAM.
In Page Mode, the upper 12 - 16 VMEbus address bits are provided by a 16-bit
Page Register located on the VMEbus adapter card. The remaining 16 - 20
lower address bits are provided by the address offset in the SBus slot I/O
window.
If your program enables the Address Page Register by setting this bit, it must
write to the Page Registers after the bit is set, even if correct values were
previously placed in the registers. Otherwise, the Page Register values may
not be correctly gated out to the VMEbus.
Direct Mode is used if the
Page Mode
bit is not set ("0"). The
Address Bias
jumpers are ignored if Page Mode is selected.
Содержание 466-1
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Страница 52: ...Model 466 1 Adapter 42 VMEbus Adapter Card Configuration...
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Страница 88: ...Model 466 1 Adapter 78 Common Problems And Solutions...
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Страница 107: ...Model 466 1 Adapter Jumper Configuration Worksheets 97 D 1 SBus Adapter Card Worksheet J1...
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