DMA Transfer Source Address Low 0 (SAR_LO0) – Offset 800 - 001 - ID:834576 | Intel® 800 Series Chipset Family Platform Controller Hub (PCH), Volume 2

Intel® 800 Series Chipset Family Platform Controller Hub (PCH), Volume 2

ID	Date	Version	Classification
834576	10/10/2024	001	Public

DMA Transfer Source Address Low 0 (SAR_LO0) – Offset 800

The starting source address is programmed by software before the DMA channel is enabled, or by an LLI update before the start of the DMA transfer. While the DMA transfer is in progress, this register is updated to reflect the source address
of the current transfer. Source Address Register for lower 32-bits for Channels 0-1

Bit Range	Default	Access	Field Name and Description
31:0	0h	RW	SAR_LO (SAR_LO) Current Source Address of DMA transfer. Updated after each source transfer. The SINC field in the CTL_LO[n]: Control Register determines whether the address increments or is left unchanged on every source transfer throughout the block transfer. When the channel is enabled (i.e. CH_EN is 1), the read back value will reflect the updated source transfer addresses. However, when the channel is disabled, the original programmed value will be reflected when reading this register. It's important to notice the following: 1. Once the block transfer is in progress (i.e. when channel is enabled), the read-back value correlates with the OCP Read Address that one would see in an OCP tracker. 2. If the read to this register comes during a block transfer, the LAST DMA Read address sent on the OCP before the register read is what's reflected in the read-back value. 3. If the last DMA read was a burst read (i.e. burst length ) 1), the read-back value reflects the first address of the burst read since this is what gets sent on the OCP fabric. 4. If the read to the register occurred after the whole block got transferred, then the channel gets disabled and the returned value would be the original programmed value. 5. Since the read-back value is OCP based, only DW aligned addresses will be reflected (i.e. OCP Byte-Enable values would not be reflected) 6. Based on the above remarks, this value should be used as pseudo DMA read progress indicator when the channel is enabled and not an absolute one. Decrementing addresses are not supported

Bit Range

Default

Access

Field Name and Description

31:0

SAR_LO (SAR_LO)

Current Source Address of DMA transfer.
Updated after each source transfer. The SINC field in the CTL_LO[n]: Control Register
determines whether the address increments or is left unchanged on every source transfer
throughout the block transfer. When the channel is enabled (i.e. CH_EN is 1), the read
back value will reflect the updated source transfer addresses. However, when the
channel is disabled, the original programmed value will be reflected when reading this
register.
It's important to notice the following:
1. Once the block transfer is in progress (i.e. when channel is enabled), the read-back
value correlates with the OCP Read Address that one would see in an OCP tracker.
2. If the read to this register comes during a block transfer, the LAST DMA Read
address sent on the OCP before the register read is what's reflected in the read-back
value.
3. If the last DMA read was a burst read (i.e. burst length ) 1), the read-back value
reflects the first address of the burst read since this is what gets sent on the OCP fabric.
4. If the read to the register occurred after the whole block got transferred, then the
channel gets disabled and the returned value would be the original programmed value.
5. Since the read-back value is OCP based, only DW aligned addresses will be reflected
(i.e. OCP Byte-Enable values would not be reflected)
6. Based on the above remarks, this value should be used as pseudo DMA read progress
indicator when the channel is enabled and not an absolute one.
Decrementing addresses are not supported