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Section 20 USB Function Module
Rev. 4.00 Sep. 14, 2005 Page 780 of 982
REJ09B0023-0400
20.6 Stall
Operations
This section describes stall operations in the USB function module. There are two cases in which
the USB function module stall function is used:
•
When the application forcibly stalls an endpoint for some reason
•
When a stall is performed automatically within the USB function module due to a USB
specification violation
The USB function module has internal status bits that hold the status (stall or non-stall) of each
endpoint. When a transaction is sent from the host, the module references these internal status bits
and determines whether to return a stall to the host. These bits cannot be cleared by the
application; they must be cleared with a Clear Feature command from the host. The internal status
bit for EP0 is automatically cleared only when the setup command is received.
20.6.1
Forcible Stall by Application
The application uses USBEPSTL register to issue a stall request for the USB function module.
When the application wishes to stall a specific endpoint, it sets the corresponding bit in
USBEPSTL (1-1 in figure 20.13). The internal status bits are not changed. When a transaction is
sent from the host for the endpoint for which the USBEPSTL bit was set, the USB function
module references the internal status bit, and if this is not set, references the corresponding bit in
USBEPSTL (1-2 in figure 20.13). If the corresponding bit in USBEPSTL is set, the USB function
module sets the internal status bit and returns a stall handshake to the host (1-3 in figure 20.13). If
the corresponding bit in USBEPSTL is not set, the internal status bit is not changed and the
transaction is accepted.
Once an internal status bit is set, it remains set until cleared by a Clear Feature command from the
host, without regard to USBEPSTL register. Even after a bit is cleared by the Clear Feature
command (3-1 in figure 20.13), the USB function module continues to return a stall handshake
while the bit in USBEPSTL is set, since the internal status bit is set each time a transaction is
executed for the corresponding endpoint (1-2 in figure 20.13). To clear a stall, therefore, it is
necessary for the corresponding bit in USBEPSTL to be cleared by the application, and also for
the internal status bit to be cleared with a Clear Feature command (2-1, 2-2, and 2-3 in figure
20.13).
Summary of Contents for HD6417641
Page 2: ...Rev 4 00 Sep 14 2005 Page ii of l...
Page 7: ...Rev 4 00 Sep 14 2005 Page vii of l...
Page 11: ...Rev 4 00 Sep 14 2005 Page xi of l USB Universal serial bus WDT Watch dog timer...
Page 12: ...Rev 4 00 Sep 14 2005 Page xii of l...
Page 28: ...Rev 4 00 Sep 14 2005 Page xxviii of l...
Page 204: ...Section 4 Clock Pulse Generator CPG Rev 4 00 Sep 14 2005 Page 154 of 982 REJ09B0023 0400...
Page 212: ...Section 5 Watchdog Timer WDT Rev 4 00 Sep 14 2005 Page 162 of 982 REJ09B0023 0400...
Page 228: ...Section 6 Power Down Modes Rev 4 00 Sep 14 2005 Page 178 of 982 REJ09B0023 0400...
Page 246: ...Section 8 X Y Memory Rev 4 00 Sep 14 2005 Page 196 of 982 REJ09B0023 0400...
Page 318: ...Section 11 User Break Controller UBC Rev 4 00 Sep 14 2005 Page 268 of 982 REJ09B0023 0400...
Page 454: ...Section 12 Bus State Controller BSC Rev 4 00 Sep 14 2005 Page 404 of 982 REJ09B0023 0400...
Page 504: ...Section 14 U Memory Rev 4 00 Sep 14 2005 Page 454 of 982 REJ09B0023 0400...
Page 566: ...Section 17 Compare Match Timer CMT Rev 4 00 Sep 14 2005 Page 516 of 982 REJ09B0023 0400...
Page 868: ...Section 21 A D Converter Rev 4 00 Sep 14 2005 Page 818 of 982 REJ09B0023 0400...
Page 914: ...Section 23 I O Ports Rev 4 00 Sep 14 2005 Page 864 of 982 REJ09B0023 0400...
Page 956: ...Section 24 List of Registers Rev 4 00 Sep 14 2005 Page 906 of 982 REJ09B0023 0400...
Page 1016: ...Section 25 Electrical Characteristics Rev 4 00 Sep 14 2005 Page 966 of 982 REJ09B0023 0400...
Page 1024: ...Appendix Rev 4 00 Sep 14 2005 Page 974 of 982 REJ09B0023 0400...
Page 1032: ...Rev 4 00 Sep 14 2005 Page 982 of 982 REJ09B0023 0400 X X Y data addressing 52 X Y memory 193...
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