
82801AA and 82801AB Datasheet
9-13
IDE Controller Registers (D31:F1)
9.2.2
BMIS[P,S]—Bus Master IDE Status Register
Address Offsets:
Primary: 02h
Secondary: 0Ah
00h
Attribute:
R/WC
Default Value:
Size:
8 bits
9.2.3
BMID[P,S]—Bus Master IDE Descriptor Table Pointer
Register
Address Offsets:
Primary: 04h
Secondary: 0Ch
All bits undefined
Attribute:
R/W
Default Value:
Size:
32 bits
Bit
Description
7
Reserved. Must return 0 on reads.
6
Drive 1 DMA Capable.
1 = Capable. This read/write bit is set by device dependent code (BIOS or device driver) to indicate
that drive 1 for this channel is capable of DMA transfers, and that the controller has been
initialized for optimum performance. The ICH does not use this bit. It is intended for systems that
do not attach BMIDE to the PCI bus.
0 = Not Capable.
5
Drive 0 DMA Capable.
1 = Capable. This read/write bit is set by device dependent code (BIOS or device driver) to indicate
that drive 0 for this channel is capable of DMA transfers, and that the controller has been
initialized for optimum performance. The ICH does not use this bit. It is intended for systems that
do not attach BMIDE to the PCI bus.
0 = Not Capable.
4:3
Reserved. Must return 0 on reads.
2
Interrupt.
Software can use this bit to determine if an IDE device has asserted its interrupt line.
When this bit is read as a one, all data transferred from the drive is visible in system memory. If the
interrupt status bit is cleared (by writing a 1 to this bit), while the interrupt is still active, this bit will
remain clear until another assertion edge is detected on the interrupt line.
1 = This bit is set by the rising edge of the IDE interrupt line.
0 = This bit is cleared when a '1' is written to it by software.
IRQ14
Primary Channel interrupt
IRQ15
Secondary Channel interrupt
This bit is set independent of whether the bit is masked in the 8259 or the internal I/O APIC.
1
Error.
1 = This bit is set when the controller encounters a target abort or master abort when transferring
data on PCI.
0 = This bit is cleared when a '1' is written to it by software.
0
Bus Master IDE Active (ACT)—RO.
1 = Set by the ICH when the Start bit is written to the Command register.
0 = This bit is cleared by the ICH when the last transfer for a region is performed, where EOT for that
region is set in the region descriptor. It is also cleared by the ICH when the Start bit is cleared in
the Command register. When this bit is read as a zero, all data transferred from the drive during
the previous bus master command is visible in system memory, unless the bus master
command was aborted.
Bit
Description
31:2
Base address of Descriptor table (BADDR).
Corresponds to A[31:2]. The Descriptor Table must be
DWord aligned. The Descriptor Table must not cross a 64K boundary in memory.
1:0
Reserved.