Intel C2518 FH8065501516710 Data Sheet
Product codes
FH8065501516710
Volume 2—Universal Serial Bus (USB) 2.0—C2000 Product Family
USB 2.0 Based Debug Port
Intel
®
Atom™ Processor C2000 Product Family for Microserver
Datasheet, Vol. 2 of 3
September 2014
278
Order Number: 330061-002US
14.12.1
Theory of Operation
Two operational modes for the USB debug port are:
• Mode 1 – The USB port is in a disabled state from the viewpoint of a standard host
controller driver. That is, when the Host Controller Run/Stop bit is 0. In Mode 1, the
debug port controller is required to generate a keepalive packets less than 2 ms
apart to keep the attached debug device from suspending. The keepalive packet is
a standalone 32-bit SYNC field.
• Mode 2 – The host controller is running (Host Controller Run/Stop bit is 1). In
Mode 2, the normal transmission of SOF packets keeps the debug device from
suspending.
Behavioral Rules
• In both Modes 1 and 2, the debug port controller must check for software-
requested debug transactions at least every 125 microseconds.
• If the debug port is enabled by the debug driver, and the standard host controller
driver resets the USB port, USB debug transactions are held off for the duration of
the reset and until after the first SOF is sent.
• If the standard host controller driver suspends the USB port, then USB debug
transactions are held off for the duration of the suspend/resume sequence and until
after the first SOF is sent.
Table 14-7. Debug Port Behavior
OWNER_CNT
ENABLED_CT
Port
Enable
Run /
Stop
Suspend
Debug Port Behavior
0
X
X
X
X
Debug port is not being used. Normal
operation.
1
0
X
X
X
Debug port is not being used. Normal
operation.
1
1
0
0
X
Debug port in Mode 1. SYNC
keepalives sent plus debug traffic
1
1
0
1
X
Debug port in Mode 2. SOF (and only
SOF) is sent as keepalive. Debug
traffic is also sent.
Note:
No other normal traffic is sent
out this port, because the port
is not enabled.
1
1
1
0
0
Invalid. Host controller driver does not
put the controller into this state
(enabled, not running and not
suspended).
1
1
1
0
1
Port is suspended. No debug traffic
sent.
1
1
1
1
0
Debug port in Mode 2. Debug traffic is
interspersed with normal traffic.
1
1
1
1
1
Port is suspended. No debug traffic
sent.