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(3) Automatic Stall by USB Function Module
When a stall setting is made with the Set Feature command, when the information of this
module differs from that returned to the host by the Get Descriptor, or in the event of a USB
specification violation, the USB function module automatically sets the internal status bit for
the relevant endpoint without regard to EPnSTL, and returns a stall handshake (1-1 in figure
15.23).
Once an internal status bit is set, it remains set until cleared by a Clear Feature command from
the host, without regard to EPnSTL. After a bit is cleared by the Clear Feature command,
EPnSTL is referenced (3-1 in figure 15.23). The USB function module continues to return a
stall handshake while the internal status bit is set, since the internal status bit is set even if a
transaction is executed for the corresponding endpoint (2-1 and 2-2 in figure 15.23). To clear a
stall, therefore, the internal status bit must be cleared with a Clear Feature command (3-1 in
figure 15.23). If set by the firmware, EPnSTL should also be cleared (2-1 in figure 15.23).
Rev. 3.0, 10/02, page 511 of 686
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