82801FB Datasheet, PDF (452/786 Pages) Intel Corporation – Intel I/O Controller Hub 6 (ICH6) Family

IDE Controller Registers (D31:F1)
11.2.1
BMICP—Bus Master IDE Command Register
(IDE—D31:F1)
Address Offset: BMIBASE + 00h
Default Value: 00h
Attribute:
Size:
R/W
8 bits
Bit
Description
7:4 Reserved. Returns 0.
Read / Write Control (RWC) — R/W. This bit sets the direction of the bus master transfer: This bit
must NOT be changed when the bus master function is active.
3
0 = Memory reads
1 = Memory writes
2:1 Reserved. Returns 0.
Start/Stop Bus Master (START) — R/W.
0 = All state information is lost when this bit is cleared. Master mode operation cannot be stopped
and then resumed. If this bit is reset while bus master operation is still active (i.e., the Bus
Master IDE Active bit (BMIBASE + 02h, bit 0) of the Bus Master IDE Status register for that IDE
channel is set) and the drive has not yet finished its data transfer (the Interrupt bit (BMIBASE +
02h, bit 2) in the Bus Master IDE Status register for that IDE channel is not set), the bus master
command is said to be aborted and data transferred from the drive may be discarded instead of
being written to system memory.
0 ^{1 = Enables bus master operation of the controller. Bus master operation does not actually start}
unless the Bus Master Enable bit (D31:F1:04h, bit 2) in PCI configuration space is also set. Bus
master operation begins when this bit is detected changing from 0 to 1. The controller will
transfer data between the IDE device and memory only when this bit is set. Master operation
can be halted by writing a 0 to this bit.
NOTE: This bit is intended to be cleared by software after the data transfer is completed, as
indicated by either the Bus Master IDE Active bit being cleared or the Interrupt bit of the Bus
Master IDE Status register for that IDE channel being set, or both. Hardware does not clear
this bit automatically.
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Intel^® I/O Controller Hub 6 (ICH6) Family Datasheet