TUSB3410 datasheet(77/92 Pages) TI

77 / 92 page

11–7

11.4.2 Descriptor Block

Each descriptor block contains prefix and content. The size of the prefix is always 4 bytes. It contains the data type,

size, and checksum for data integrity. The descriptor content contains the corresponding information specified in the

prefix. It could be as small as 1 byte or as large as 65535 bytes. The next descriptor immediately follows the previous

descriptor. If there are no more descriptors, an extra byte with a value of zero should be added to indicate the end

of header.

11.4.2.1 Descriptor Prefix

The first byte of the descriptor prefix is the data type. This tells the bootcode how to process the data in the descriptor

content. The second and third bytes are the size of descriptor content. The second byte is the low byte of the size

and the third byte is the high byte. The last byte is the 8-bit arithmetic checksum of descriptor content.

11.4.2.2 Descriptor Content

Information stored in the descriptor content can be the USB information, firmware, or other type of data. The size of

the content should be from 1 byte to 65535 bytes.

11.5 Checksum in Descriptor Block

Each descriptor prefix contains one checksum of the descriptor content. If the checksum is wrong, the bootcode

simply ignores the descriptor block.

11.6 Header Examples

The header can be specified in different ways. The following descriptors show examples of the header format and

the supported descriptor block.

11.6.1 TUSB3410 Bootcode Supported Descriptor Block

The TUSB3410 bootcode supports the following descriptor blocks.

•

USB Device Descriptor

•

USB Configuration Descriptor

•

USB String Descriptor

•

Binary Firmware1

•

Autoexec Binary Firmware2

1 Binary firmware is loaded when the bootcode receives the first get device descriptor request from host. Downloading the firmware should

either continue that request in the data stage or disconnect from the USB and then reconnect to the USB as a new device.

2 The bootcode loads this autoexec binary firmware before it connects to the USB. The firmware should connect to the USB once it is

loaded.

TUSB3410 датащи(PDF) 77 Page - Texas Instruments