HD6417705F133V Datasheet, PDF (515/741 Pages) Renesas Technology Corp – Renesas 32-Bit RISC Microcomputer SuperH RISC engine Family/SH7700 Series

18.6.3 Automatic Stall by USB Function Module
When a stall setting is made with the Set Feature command, 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 the EPSTL register, and returns a stall handshake (1-1 in figure 18.14).
Once an internal status bit is set, it remains set until cleared by a Clear Feature command from the
host, without regard to the EPSTL register. After a bit is cleared by the Clear Feature command,
EPSTL is referenced (3-1 in figure 18.14). 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 18.14). To clear a stall, therefore,
the internal status bit must be cleared with a Clear Feature command (3-1 in figure 18.14). If set
by the application, EPSTL should also be cleared (2-1 in figure 18.14).
(1) Transition from normal operation to stall
(1-1)
STALL handshake
Internal status bit
0→1
EPSTL
0
To (2-1) or (3-1)
1. In case of USB
specification
violation, etc., USB
function module
stalls endpoint
automatically
(2) When transaction is performed when internal status bit is set, and Clear Feature is sent
(2-1)
Transaction request
Internal status bit
1
(2-2)
EPSTL
0
1. EPSTL cleared to 0
by application
2. IN/OUT token
received from host
3. Internal status bit
already set to 1
4. EPSTL not
referenced
5. Internal status bit
not changed
STALL handshake
Internal status bit
1
EPSTL
0
1. Transmission of
STALL handshake
Stall status maintained
(3) When Clear Feature is sent before transaction is performed
(3-1)
Clear Feature command
Internal status bit
1→0
EPSTL
0
1. Internal status bit
cleared to 0
2. EPSTL not changed
Normal status restored
Figure 18.14 Automatic Stall by USB Function Module
Rev. 2.00, 09/03, page 467 of 690