Streaming Transfer Time for PIO and DMA Modes

e02127r0

Streaming Transfer Time for PIO and DMA modes

To: T13 Technical committee

From: Sumit Puri

Fujitsu Computer Products

2904 Orchard Parkway

San Jose, CA 95134

Phone: 408-570-4070

Fax: 408-570-4009

Email:

Date: 8-19-2002

1.0 Introduction

The purpose of this proposal is to add additional information to the IDENTIFY DEVICE data to support Streaming Transfer Time values for PIO and DMA modes in the AV command set. The previous definition of the IDENTIFY DEVICE data defined word 96 as the Streaming Transfer Time, but did not define if it was for PIO or DMA mode. This proposal redefines word 96 of the IDENTIFY DEVICE data as the Streaming Transfer for DMA, also word XX has been added as the Streaming Transfer Time for PIO.

Because the contents of word 97, Streaming Access Latency for AV command set, it is required that Access Latency also be defined independently for PIO and DMA modes. This proposal redefines word 97 of the IDENTIFY DEVICE data as the Streaming Access Latency for DMA, also word XX has been added as the Streaming Access Latency for PIO.

2.0 Proposed Specification Changes

The following changes are proposed for the ATA-7 specification

· Modify the IDENTIFY DEVICE data to show values for Streaming Transfer Time for both PIO and UDMA. The current specification does not specify if the contents of word 96 is for PIO or DMA mode.

5.16 Changes to IDENTIFY DEVICE data

Word / O/M / F/V / Description
Word 96 / V / Streaming Transfer Time – DMA
Word XX / V / Streaming Transfer Time – PIO
Word / O/M / F/V / Description
Word 97 / V / Streaming Access Latency – DMA
Word XX / V / Streaming Access Latency – PIO

5.16.52 Word 96: Streaming Transfer Time - DMA

Word 96 defines the Streaming Transfer Time for DMA mode.

The worst-case sustainable transfer time per sector for the device is calculated as follows:

Streaming Transfer Time DMA = (word 96) * (words (99:98) / 65536)

The content of IDENTIFY DEVICE word 96 may be affected by the host issuing a SET FEATURES subcommand 42h, C2h or 43h (Automatic Acoustic Management, and Typical Host Interface Sector Time).

Because of this effect, an IDENTIFY DEVICE command shall be issued after a SET FEATURES command that may affect these words. If the Streaming Feature Set is not supported by the device, the content of word 96 shall be zero.

5.16.XX Word XX: Streaming Transfer Time – PIO

Word XX defines the Streaming Transfer Time for PIO mode.

The worst-case sustainable transfer time per sector for the device is calculated as follows:

Streaming Transfer Time = (word XX) * (words (99:98) / 65536)

The content of IDENTIFY DEVICE word XX may be affected by the host issuing a SET FEATURES subcommand 42h, C2h or 43h (Automatic Acoustic Management, and Typical Host Interface Sector Time).

5.16.53 Word 97: Streaming Access Latency - DMA

Word 97 defines the Streaming Access Latency for DMA mode.

The worst-case access latency of the device for a streaming command is calculated as follows:

Access Latency = (word 96) * (words (99:98) / 256)

The content of IDENTIFY DEVICE word 97 may be affected by the host issuing a SET FEATURES subcommand 42h, C2h or 43h (Automatic Acoustic Management, and Typical Host Interface Sector Time).

5.16.xx Word xx: Streaming Access Latency - PIO

Word 97 defines the Streaming Access Latency for PIO mode.

The worst-case access latency of the device for a streaming command is calculated as follows:

Access Latency = (word XX) * (words (99:98) / 256)

The content of IDENTIFY DEVICE word 97 may be affected by the host issuing a SET FEATURES subcommand 42h, C2h or 43h (Automatic Acoustic Management, and Typical Host Interface Sector Time).

5.16.54 Words (99:98): Streaming Performance Granularity

These words define the fixed unit of time that is used in IDENTIFY DEVICE words (97:96), and SET FEATURES subcommand 43h, and in the Streaming Performance Parameters log, which is accessed by use of the READ LOG EXT command, and in the Command Completion Time Limit that is passed in streaming commands. The unit of time for this parameter shall be in microseconds. For example, if yy was returned by the drive for this parameter, then

- the Command Completion Time Limit in the features register shall be in units yy ms

- word 96, word XX, and the Sector Time array entries in the Streaming Performance Parameters log shall be in units per sector of yy ms / 65536.

- word 97, word XX, and the Access Time array entries in the Streaming Performance Parameters log shall be in units of yy ms / 256.

- taking these units into account, the host may calculate the estimated time for a streaming command of size S sectors as ( ( word 96 * S / 65536) + (word 97 / 256 )) * yy microseconds for DMA mode.

- taking these units into account, the host may calculate the estimated time for a streaming command of size S sectors as ( ( word XX * S / 65536) + (word XX / 256 )) * yy microseconds for PIO mode.

The value of the Streaming Performance Granularity is vendor specific and fixed for a device.

5.49.18 Set Maximum Host Interface Sector Times

Subcommand code 43h allows the host to inform the device of a host interface rate limitation. This information shall be used by the device to meet the Command Completion Time Limits of the commands of the streaming feature set. To inform the device of a host interface rate limitation, the host writes the LSB and MSB value of its Typical PIO Host Interface Sector Time to the Sector Count and LBA Low registers and writes the LSB and MSB value of its Typical DMA Host Interface Sector Time to the LBA Mid and LBA High registers. The Typical Host Interface Sector Times have the same units as IDENTITY DEVICE word 96 for DMA and word XX for PIO. A value of zero indicates that the host interface shall be capable of transferring data at the maximum rate allowed by the selected transfer mode. The Typical PIO Mode Host Interface Sector Time includes the host’s interrupt service time.