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3.16
Device States Changed Handler
SPRU761A
This section describes how USB device states and transitions states are
decoded by the USB device controller and how they can be handled.
The state machine (see Figure 22) shows how the USB device controller
device moves from one state to another state with respect to the USB1.1
specification. Attach/unattach transition is not shown in the transition flow.
Because SET_CONFIGURATION is not decoded by the core, the MPU has
the responsibility to distinguish a SET_CONFIGURATION with a nonvalid
configuration value from other SET_CONFIGURATION requests and to set
SYSCON2.DEV_CFG only if the configuration value is valid (value 0 is
nonvalid), when the device is in addressed state. When the device is in
configured state, the MPU has the responsibility to set SYSCON2.CLR_CFG
if the configuration number is 0 so that the device moves to addressed state.
Device states are visible in the DEVSTAT register and are decoded as follows.
-
Attached: The device is attached to the USB and powered.
-
Default: The device is attached to the USB, is powered, and has been
reset.
-
Addressed: The device is attached to the USB, is powered, has been
reset, and an address has been assigned. The device moves into the
addressed state after a SET_ADDRESS request with an address number
other than 0.
-
Configured: The device is attached to the USB, is powered, has been
reset, has an address other than 0, and is configured. The device moves
into the configured state after a valid SET_CONFIGURATION request,
only if the MPU has set the SYSCON2.DEV_CFG bit (meaning the
configuration is valid).
-
Suspended: The device is at minimum default and has not seen bus
activity for 5 ms.
-
Reset: When set, the device is receiving a valid USB host reset.
-
R_WK_OK: This bit is set (cleared) automatically after a valid
SET_DEVICE_FEATURE (CLEAR_DEVICE_FEATURE) request from
the USB host.
Any change in the DEVSTAT register bits triggers a device change interrupt
(IRQ_SRC.DS_CHG), if enabled.
The device moves to addressed state after the status stage of a valid
SET_ADDRESS, even if the status stage ACK handshake is received
USB Device Controller
Universal Serial Bus (USB)
157
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