Usage Notes and Known Design Exceptions to Functional Specifications
Advisory 1.0.7
Boot: Ethernet Boot ROM Code PHY Link Speed Detection
Revisions Affected
1.0
Details
The device ROM code relies on the external PHY's Control Register (Register 0),
specifically bits 0.6 [Speed Selection (MSB)] and 0.13 [Speed Selection (LSB)], to
determine the operating speed of the link.
If the external PHY does not update its link speed selection bits to reflect the current
operating speed, the ROM code incorrectly assumes the PHY is operating at the speed
indicated by the link speed selection bits and configure the device Ethernet MAC to the
wrong speed. For example, if the default value of the PHY link speed selection bits
indicates 100 Mbps, when the PHY is actually operating at 1 Gbps, the ROM incorrectly
configures the device Ethernet MAC for 100 Mbps mode.
The IEEE 802.3 specification states:
When the Auto-Negotiation Enable (bit 0.12) is
enabled, bits 0.6 and 0.13 can be read or written to, but the state of bits 0.6 and 0.13
have no effect on the link configuration, and it is not necessary for bits 0.6 and 0.13 to
reflect the operating speed of the link when it is read
. While some PHYs update the link
speed in these bits to reflect the current operating speed, other PHYs do not update
these bits because it is not mandatory according to the specification.
Workarounds
When using Ethernet boot, an external PHY that updates the Register 0 link speed
selection bits (0.6 and 0.13) to reflect the current operating speed is required.
Advisory 1.0.8
Boot: Ethernet Boot ROM Code Sends an Incorrect Vendor Class Identifier in
BOOTP Packet
Revisions Affected:
1.0
Details:
When using Ethernet boot, the device ROM code should send a BOOTP request with a
unique identifier to distinguish itself from other devices on the same network. Instead,
the ROM code sends the same identifier, "DM814x ROM v1.0", for all devices (DM814x,
DM816x, and AM335x); hence, the download host attempting to bootstrap the devices
can no longer determine which device is requesting the code to be downloaded.
Applications using the DM814x, DM816x, and AM335x devices cannot coexist in the
same network if they are booted from Ethernet.
Workaround:
There is no workaround for this issue.
For some applications, it might be necessary to uniquely identify and service BOOTP
packets from a client. The recommended approach to uniquely identify clients is to use
the MAC address. Every device comes with a unique MAC address. A list of MAC
addresses and the device type can be made available to the host in advance, so that the
host can take device-specific action when it receives a BOOTP packet from a MAC
address on the host's list.
14
SPRZ360F – October 2011 – Revised November 2013
Sitara™ AM335x ARM
®
Cortex™-A8 Microprocessors (MPUs) (Silicon
Revision 2.1, 2.0, 1.0)
Copyright © 2011–2013, Texas Instruments Incorporated
