215
XMEGA B [DATASHEET]
8291B–AVR–01/2013
Figure 18-7. Clock generation configuration.
18.6
Ping-pong Operation
When an endpoint is configured for ping-pong operation, it uses the input and output data buffers to create a single,
double-buffered endpoint that can be set to input or output direction. This provides double-buffered communication, as
the CPU or DMA controller can access one of the buffers, while the other buffer is processing an ongoing transfer. Ping-
pong operation is identical to the IN and OUT transactions described above, unless otherwise noted in this section. Ping-
pong operation is not possible for control endpoints.
When ping-pong operation is enabled for an endpoint, the endpoint in the opposite direction must be disabled. The data
buffer, data pointer, byte counter, and auxiliary data from the enabled endpoint are used as bank 0, and,
correspondingly, bank 1 for the opposite endpoint direction.
The bank select (BANK) flag in the endpoint STATUS register indicates which data bank will be used in the next
transaction. It is updated after each transaction. The TRNCOMPL0/TRNCOMPL1, underflow/overflow (UDF/OVF), and
CRC flags in the STATUS register are set for either the enabled or the opposite endpoint direction according to the BANK
flag. The data toggle (TOGGLE), data buffer 0/1 not acknowledge (BUSNACK0 and BUSNACK1), and BANK flags are
updated for the enabled endpoint direction only.
Figure 18-8. Ping-pong operation overview.
USB module
48MHz full speed
6MHz for low speed
USBSRC
USB clock
prescaler
USBPSDIV
PLL
48MHz Internal Oscillator
Bank0
Available time for data processing by CPU to avoid NACK
Without Ping-Pong
With Ping-Pong
Bank1
Endpoint
single bank
Endpoint
Double bank
USB data packet
t
t
Содержание XMEGA B
Страница 320: ...320 XMEGA B DATASHEET 8291B AVR 01 2013 Table 25 12 7 segments Character Table...
Страница 321: ...321 XMEGA B DATASHEET 8291B AVR 01 2013 Table 25 13 14 segments Character Table...
Страница 322: ...322 XMEGA B DATASHEET 8291B AVR 01 2013 Table 25 14 16 segments Character Table...
Страница 412: ...412 XMEGA B DATASHEET 8291B AVR 01 2013...
Страница 413: ...413 XMEGA B DATASHEET 8291B AVR 01 2013...
Страница 414: ...414 XMEGA B DATASHEET 8291B AVR 01 2013...