FW82801DBM S L6DN Intel, FW82801DBM S L6DN Datasheet - Page 105

• Manufacturer Part Number: FW82801DBM S L6DN
• Manufacturer: Intel

Specifications of FW82801DBM S L6DN

• Lead Free Status / RoHS Status: Not Compliant

5.5.6
5.5.7
5.5.8
Intel
®
Figure 5-11. DMA Request Assertion Through LDRQ#
82801DBM ICH4-M Datasheet
DMA Cycle Termination
DMA cycles are terminated when a terminal count is reached in the DMA controller and the
channel is not in autoinitialize mode, or when the PC/PCI device deasserts its request. The PC/PCI
device must follow explicit rules when deasserting its request, or the ICH4 may not see it in time
and run an extra I/O and memory cycle.
The PC/PCI device must deassert its request 7 PCICLKs before it generates TRDY# on the I/O
read or write cycle, or the ICH4 is allowed to generate another DMA cycle. For transfers to
memory, this means that the memory portion of the cycle is run without an asserted PC/PCI REQ#.
LPC DMA
DMA on LPC is handled through the use of the LDRQ# lines from peripherals and special
encodings on LAD[3:0] from the host. Single, Demand, Verify, and Increment modes are supported
on the LPC interface. Channels 0–3 are 8 bit channels. Channels 5–7 are 16-bit channels. Channel
4 is reserved as a generic bus master request.
Asserting DMA Requests
Peripherals that need DMA service encode their requested channel number on the LDRQ# signal.
To simplify the protocol, each peripheral on the LPC interface has its own dedicated LDRQ# signal
(they may not be shared between two separate peripherals). The ICH4 has two LDRQ# inputs,
allowing at least two devices to support DMA or bus mastering.
LDRQ# is synchronous with LCLK (PCI clock). As shown in
following serial encoding sequence:
If another DMA channel also needs to request a transfer, another sequence can be sent on LDRQ#.
For example, if an encoded request is sent for channel 2 and then channel 3 needs a transfer before
the cycle for channel 2 is run on the interface, the peripheral can send the encoded request for
channel 3. This allows multiple DMA agents behind an I/O device to request use of the LPC
interface and the I/O device does not need to self-arbitrate before sending the message.
•
•
•
•
LDRQ#
Peripheral starts the sequence by asserting LDRQ# low (start bit). LDRQ# is high during idle
conditions.
The next 3 bits contain the encoded DMA channel number (MSB first).
The next bit (ACT) indicates whether the request for the indicated DMA channel is active or
inactive. The ACT bit will be a 1(high) to indicate if it is active and 0 (low) if it is inactive.
The case where ACT is low is rare, and is only used to indicate that a previous request for that
channel is being abandoned.
After the active/inactive indication, the LDRQ# signal must go high for at least 1 clock. After
that one clock, LDRQ# signal can be brought low to the next encoding sequence.
LCLK
Start
MSB
LSB
Figure 5-11
ACT
Functional Description
the peripheral uses the
Start
105