Cypress Semiconductor FX2LP Technical Information Seite 366

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EZ-USB FX2 Technical Reference Manual
Page 15-46 EZ-USB FX2 Technical Reference Manual v2.1
Do not clear an IRQ bit by reading an IRQ Register, ORing its contents with a bit mask, and writ-
ing back the IRQ Register. This will clear ALL pending interrupts. Instead, simply write the bit mask
value (with a 1 in the bit position of the IRQ you want to clear) directly to the IRQ Register.
15.7.3 Endpoint Ping-NAK/IBN Interrupt Enable/Request
Figure 15-41. Endpoint Ping-NAK/IBN Interrupt Enable
Figure 15-42. Endpoint Ping-NAK/IBN Interrupt Request
Bit 7-2 EP[8,6,4,2,1,0] Ping-NAK INT Enable/Request
These registers are active only during high speed (480 Mbits/sec) operation.
USB 2.0 improves the USB 1.1 bus bandwidth utilization by implementing a PING-NAK mech-
anism for OUT transfers. When the host wishes to send OUT data to an endpoint, it first sends
a PING token to see if the endpoint is ready, i.e. it has an empty buffer. If a buffer is not avail-
able, the SIE returns a NAK handshake. PING-NAK transactions continue to occur until an
OUT buffer is available, at which time the FX2 SIE answers a PING with an ACK handshake.
Then the host sends the OUT data to the endpoint.
The OUT Ping NAK interrupt indicates that the host is trying to send OUT data, but the SIE
responded with a NAK because no endpoint buffer memory is available. The firmware may
wish to use this interrupt to free up an OUT endpoint buffer.
NAKIE Endpoint Ping-NAK/IBN Interrupt Enable (INT2) E65A
b7 b6 b5 b4 b3 b2 b1 b0
EP8 EP6 EP4 EP2 EP1 EP0 0 IBN
R/W R/W R/W R/W R/W R/W R/W R/W
0 0 0 0 0 0 0 0
NAKIRQ Endpoint Ping-NAK/IBN Interrupt Request (INT2) E65B
b7 b6 b5 b4 b3 b2 b1 b0
EP8 EP6 EP4 EP2 EP1 EP0 0 IBN
R/W R/W R/W R/W R/W R/W R/W R/W
0 0 0 0 0 0 0 0
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