Datasheet

Functional Description
70 Intel® Xeon® Processor D-1500 Product Family
Datasheet - Volume 1 of 4: Integrated Platform Controller Hub
March 2015
3.5.5 Software Commands
There are three additional special software commands that the DMA controller can
execute. The three software commands are:
• Clear Byte Pointer Flip-Flop
•Master Clear
• Clear Mask Register
They do not depend on any specific bit pattern on the data bus.
3.6 Low Pin Count (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.
3.6.1 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 I/F has its own
dedicated LDRQ# signal (they may not be shared between two separate peripherals).
Intel® Xeon® Processor D-1500 Product Family 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 Figure 3-4, the peripheral
uses the following serial encoding sequence:
• Peripheral starts the sequence by asserting LDRQ# low (start bit). LDRQ# is high
during idle conditions.
• The next three 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 is 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
one clock. After that one clock, LDRQ# signal can be brought low to the next
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.