TAS1020APFB datasheet(21/114 Pages) TI

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2.2.2.4 I2C Serial EEPROM

The TAS1020A accesses the EEPROM via an I2C serial bus. Thus the EEPROM must be an I2C serial EEPROM.

The ROM boot loader assumes the EEPROM device uses the full 7-bit I2C device address with the upper four bits

of the address (control code) set to 1010 and the three least significant bits (chip select bits) set to 000.

2.2.2.5 DFU Upgrade Process

DFU compliance provides a host the capability of upgrading application code currently residing in a target’s onboard

EEPROM memory. The DFU upgrade process provided by the TAS1020A fully conforms to the requirements

specified in USB Device Class Specification For DFU 1.0.

The download must consist of both header and application code. The destination of the download must be defined

by the on-chip application code (as opposed to the application code being downloaded). Under normal

circumstances, the download destination would be EEPROM, but it is possible for the application code to specify

on-chip RAM as the download destination.

If the download destination is to be EEPROM, bit 1 of the Attribute field in the header data being downloaded

determines whether or not the header data in the download image is to be written to the EEPROM. A bit value of 1

results in the header in the EEPROM being overwritten by the header content in the download image. It is important

to note that if the application code targets RAM as the download destination, bit 1 in the Attribute field of the download

image must be 0.

2.2.2.6 Download Error Recovery

Safeguards are incorporated on the TAS1020A ROM to allow recovery from a host download that does not complete

due to a loss of power. Before downloading the application code, the TAS1020A saves the value of the Data Type

field in the EEPROM header and modify the Data Type field to indicate that a download is in progress. After successful

completion of the download, the TAS1020A restores the saved value in the Data Type field. If the download is

terminated prior to successful completion, the Data Type field still indicates that a download is in progress. In the case

of an unsuccessful download the TAS1020A reboots as a DFU device in DFU Program mode and uses the Vendor

and Product ID from the EEPROM header as the vendor and product ID in its USB device descriptor.

The download process consists of the following task flow.

•

Header portion of download is written to EEPROM, if applicable.

•

Header Data Type is retrieved and stored in RAM.

•

Head Data Type is overwritten with a value indicating that a download is in progress.

•

Application portion of download is written to EEPROM (or to RAM).

•

Header Data Type is overwritten with the previously recorded legal value.

If the download should terminate during the downloading of the header to EEPROM, the header checksum results

in the EEPROM being declared invalid on the next boot of the TAS1020A. If the download should terminate during

the downloading of the application code, the Data Type field indicates that a download was in progress and the

TAS1020A enters the DFU program mode on the next boot.

If the TAS1020A remains powered when a premature termination of a download occurs, the TAS1020A remains in

the DFU program mode. In this case, the host can again attempt a download; the TAS1020A does not have to be

rebooted.

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