Motorola MVME172 - Manual (Page 179)

GCSR Programming Model
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GCSR Programming Model
This section describes the programming model for the Global Control and
Status Registers (GCSR) in the VMEchip2. The local bus map decoder for
the GCSR registers is included in the VMEchip2. The local bus base
address for the GCSR is $FFF40100. The registers in the GCSR are 16 bits
wide and they are byte accessible from both the VMEbus and the local bus.
The GCSR is located in the 16-bit VMEbus short I/O space and it responds
to address modifier codes $29 or $2D. The address of the GCSR as viewed
from the VMEbus depends upon the GCSR group select value XX and
GCSR board select value Y programmed in the LCSR. The board value Y
may be $0 through $E, allowing 15 boards in one group. The value $F is
reserved for the location monitors.
The VMEchip2 includes four location monitors (LM0-LM3). The location
monitors provide a broadcast signaling capability on the VMEbus. When
a location monitor address is generated on the VMEbus, all location
monitors in the group are cleared. The signal interrupts SIG0-SIG3 should
be used to signal individual boards. The location monitors are located in
the VMEbus short I/O space and the specific address is determined by the
VMEchip2 group address. The location monitors LM0-LM3 are located at
addresses $XXF1, $XXF3, $XXF5, and $XXF7 respectively. A location
monitor cycle on the VMEbus is generated by a read or write to VMEbus
short I/O address $XXFN, where XX is the group address and N is the
specific location monitor address. When the VMEchip2 generates a
location monitor cycle to the VMEbus, within its own group, the
VMEchip2 DTACKs itself. A VMEchip2 cannot DTACK location
monitor cycles to other groups.
The GCSR section of the VMEchip2 contains the following registers: a
chip ID register, a chip revision register, a location monitor status register,
an interrupt control register, a board control register, and six general
purpose registers.
The chip ID and revision registers are provided to allow software to
determine the ID of the chip and its revision level. The VMEchip2 has a
chip ID of ten. ID codes zero and one are used by the old VMEchip. The
initial revision of the VMEchip2 is zero. If mask changes are required, the
revision level is incremented.