82371FB Datasheet, PDF (78/122 Pages) Intel Corporation – 82371FB (PIIX) AND 82371SB (PIIX3) PCI ISA IDE XCELERATOR

82371FB (PIIX) AND 82371SB (PIIX3)
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2.6.2. APMS—ADVANCED POWER MANAGEMENT STATUS PORT
I/O Address:
Default Value:
Attribute:
0B3h
00h
Read/Write
This register passes status information between the OS and the SMI handler. The PIIX/PIIX3 operation is not
effected by the data in this register.
Bit
Description
7:0
APM Status Port (APMS). Writes store data in this register and reads return the last data
written.
2.7. PCI BUS Master IDE Registers
The PCI Bus master IDE function uses 16 bytes of I/O space, allocated via the BMIBA register (A PCI Base
Address register). All bus master IDE I/O space registers can be accessed as byte, word, or Dword
quantities. The description of the 16 bytes of I/O registers follows:
2.7.1. BMICOM—BUS MASTER IDE COMMAND REGISTER
Address Offset:
Default Value:
Attribute:
Primary Channel—Base + 00h; Secondary Channel—Base + 08h
00h
Read / Write
This register enables/disables bus master capability for the IDE function and provides direction control for the
IDE DMA transfers. This register also provides bits that software uses to indicate DMA capability of the IDE
device.
Bit
Description
7:4
Reserved
3
Bus Master Read/Write Control (RWCON). 0=Reads; 1=Writes. This bit must NOT be
changed when the bus master function is active.
2:1
Reserved.
0
Start/Stop Bus Master (SSBM). 1=Start; 0=Stop. When this bit is set to 1, bus master
operation starts. The controller transfers data between the IDE device and memory only when
this bit is set. Master operation can be stopped by writing a 0 to this bit. This results in all state
information being lost (i.e., master mode operation cannot be stopped and then resumed).
If this bit is set to 0 while bus master operation is still active (i.e., Bit 0=1 in the Bus Master IDE
Status Register for that IDE channel) and the drive has not yet finished its data transfer (bit
2=0 in the channel's Bus Master IDE Status Register), the bus master command is aborted
and data transferred from the drive may be discarded before being written to system memory.
This bit is intended to be set to 0 after the data transfer is completed, as indicated by either bit
0 or bit 2 being set in the IDE Channel's Bus Master IDE Status Register.
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