HOST PC
Windows/Linux
TFTP Application
RNDIS Driver
USB H/w
Device
ROM Code
TFTP Client Boot
RNDIS Class Driver
USB H/w
USB Low-level Driver
Ethernet emulation over USB cable
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Functional Description
26.1.8.6.2 Image Download Procedure
• The device supports USB client boot only.
• The ROM implements as RNDIS class driver, so the device enumerates as an ethernet port.
• Standard RNDIS drivers present on Linux and Windows are picked up during the enumeration. No
special drivers need to be installed.
• Once the enumeration is complete, the customer can download the boot image using any standard
TFTP server application.
Figure 26-25. Image Transfer for USB Boot
26.1.8.6.3 Pins Used
The list of the device pins that are configured by the ROM in the case of USB boot mode are as follows.
Please note that all the pins might not be driven at boot time.
Table 26-38. Pins Used for USB Boot
Signal Name Pin Used in Device
USB0_DM USB0_DM
USB0_DP USB0_DP
USB0_ID USB0_ID
USB0_VBUS USB0_VBUS
26.1.8.7 ASIC ID structure
The ASIC ID size is 58 bytes for UART and 81 bytes for others. The fields of this structure are unused.
This structure is included purely for legacy purposes.
26.1.9 Image Format
26.1.9.1 Overview
All preceding sections describe how the ROM Code searches and detects a boot image from a memory or
a peripheral device type. This section describes the format of the boot image.
A boot image is basically made out of two major parts:
• The software to execute
• A header containing the destination address and size of the image for non XIP memory devices
The mandatory section of a boot image contains the software which will be loaded into the memory and
executed. An overview of the image formats is shown in Figure 26-26:
4149
SPRUH73H–October 2011–Revised April 2013 Initialization
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