AHCI: ATAport Miniport Example

OutlineOutline

AHCI FeaturesGoals

Basics

AHCI ATA Miniport Design PhilosophyMemory Structures and Resources

Enumeration

IO Creation

Error Handling

Role of AHCIRole of AHCI

Industry transitioning to SATA, AHCI provides a standard interface and is facilitating adoption

Implementing AHCI interface in a controller doesn’t prevent the controller from implementing 8038i/PCIIDE

AHCI follows advancements in PCIPCI 2.3, power management, MSI, etc.

AHCI comprehends SATA features

Feature BasicsFeature Basics

8038i/PCIIDE (PATA)

Controller ResourcesIO Port

2 channel per controller

2 devices per channel

Interrupt CapabilitiesInterrupt per channel

No hot plug

No power management

No notification

IO CapabilitiesPIO interrupt per DRQ

Software queuing

Tagged Command Queuing

AHCI 1.0 (SATA)

Controller ResourcesMemory Mapped

32 channels per controller

15 devices per channel

Interrupt CapabilitiesSelective interrupt hierarchy

Hot plug supported

Link power management

Asynchronous notification

IO CapabilitiesPIO through DMA

Hardware queuing

Native Command Queueing

AHCI Design: Memory Structures and ResourcesAHCI Design: Memory Structures and Resources

Controller Extension ABAR

AdapterControl w/ IdeStart receives ABAR as part of ControllerConfiguration->ControllerResources

Channel ExtensionOne per channel

Uncached ExtensionOne per channelPage alignedContains Command List and FIS Receive Buffer

IRB ExtensionContains Command TableFirst IRB’s Extension is Page aligned, all other IRB Extensions are IRB Extension size aligned

AHCI Design: SynchronizationAHCI Design: Synchronization

Per channel, only one channel entry point will be running at a time

AdapterControlThe port driver ensures that there is no outstanding I/O on the adapter before invoking this routine.

Interrupts are enabled just before the HwControl w/ IdeStart is called. If Interrupts are enabled, the Interrupt routine may be called after this.

AHCI Design: IRB Return ValuesAHCI Design: IRB Return Values

If the IRB status is not IRB_STATUS_DEVICE_ERROR, the port assumes that the miniport has done the error translation already and so the Error register is ignored.IRB_STATUS_PENDING is used internally to signal ‘waiting on interrupt’. The miniport should not complete IRB if it is still waiting on an interrupt. IRB_STATUS_DATALENGTH_MISMATCH

Return the actual byteCountIrb->DataTransferLength -= GetBytesLeft(ChannelExtension, Irb);Don’t set this on RequestSense IRBs, as the amount of data expected is unknown

AHCI Design: IRB Return Values (con’t)AHCI Design: IRB Return Values (con’t)

IRB_STATUS_BUSY should be used when device is busy and the miniport wants the ATAport driver to retry the command.

Use BUSY with AtaPortCompleteAllActiveRequests

Always pause ATAport queues with AtaPortDeviceBusy() when returning BUSY

IRB_STATUS_SELECTION_TIMEOUT should be used when the controller is not capable of handling IO. The ATAport driver will not retry the command.

IRB_STATUS_BUS_RESET

IRB_STATUS_INVALID_REQUEST

IRB_STATUS_SUCCESS

AHCI Design: EnumerationAHCI Design: Enumeration

Port sends ID_DEVICE, then ID_PACKET_DEVICE (or vice versa)

IRBs completed with IRB_STATUS_BUSY will be retried

All other IRB status values will be interpreted as enumeration failure

Status 0xFF, 0xFE will be interpreted as no device

Enabling an AHCI channel (CMD.ST) may take milliseconds. Pausing ATAport queues can be an effective StallTimer if attempts to move the controller to P:Running are made from StartIo.

AHCI Design: Creating IOAHCI Design: Creating IO

Miniport’s create IRBs only in uncommon circumstances

Request SenseAtaPortBuildRequestSenseIrb (ChannelExtension, root IRB)

Request Sense IrbExtension is the same as the Request Sense root IRB’s IrbExtension

Don’t use SGList, use IRB Data Buffer

Read Log ExtUsed to determine NCQ failures

Set FeaturesHwInitialize

AtaPortCompleteAllActiveRequests do not complete miniport created IRBs

… however it will complete Request Sense root IRBs

AHCI Design: CrashdumpAHCI Design: Crashdump

Must be handled at any time

The miniport driver is reloaded

Only kernel, ATAport and miniport are running, therefore initialization is very fast

The port driver will only enable the channel that contains the device with the page file

The controller is very likely enabled (AE = 1) and handling IO, in which case it must be stopped and restarted

AHCI Design: MiscellaneousAHCI Design: Miscellaneous

HotplugInterrupt routine should use AtaPortDeviceArrived and AtaPortDeviceRemoved for hotplug events

Causes ATAport to invalidate device relations appropriately

Reset/Error HandlingAtaPortCompleteAllActiveRequests is very handy. Complete everything with BUSY, restore stability, and let the ATAport driver handle retrying commands

Additional ResourcesAdditional Resources

ATA Miniport InterfaceDocumented in the WDK

List of SpecificationsATA: http://www.t13.org

SATA: http://www.serialata.org

SCSI: http://www.t10.org

AHCI: http://developer.intel.com/technology/serialata/ahci.htm

WhitePapersATA Miniport Design Guide

MSI Guidance http://download.microsoft.com/download/5/7/7/577a5684-8a83-43ae-9272-ff260a9c20e2/MSI.doc

© 2005 Microsoft Corporation. All rights reserved.This presentation is for informational purposes only. Microsoft makes no warranties, express or implied, in this summary.