atmega32u4-16mu ATMEL Corporation, atmega32u4-16mu Datasheet - Page 294

• Manufacturer Part Number: atmega32u4-16mu
• Description: Atmega32u4 8-bit Avr Microcontroller With 32k Bytes Of Isp Flash And Usb Controller
• Manufacturer: ATMEL Corporation

23.14.1.1
23.15 Isochronous mode
23.15.1
294
ATmega32U4
Underflow
Abort
If the endpoint uses 2 banks, the second one can be read by the HOST while the current is
being written by the CPU. Then, when the CPU clears FIFOCON, the next bank may be already
ready (free) and TXINI is set immediately.
An “abort” stage can be produced by the host in some situations:
The KILLBK bit is used to kill the last “written” bank. The best way to manage this abort is to per-
form the following operations:
Table 23-1.
An underflow can occur during IN stage if the host attempts to read a bank which is empty. In
this situation, the UNDERFI interrupt is triggered.
An underflow can also occur during OUT stage if the host send a packet while the banks are
already full. Typically, he CPU is not fast enough. The packet is lost.
It is not possible to have underflow error during OUT stage, in the CPU side, since the CPU
should read only if the bank is ready to give data (RXOUTI=1 or RWAL=1)
• after “N” write into UEDATX
• as soon as RWAL is cleared by hardware.
• In a control transaction: ZLP data OUT received during a IN stage,
• In an isochronous IN transaction: ZLP data OUT received on the OUT endpoint during a IN
• ...
stage on the IN endpoint
Abort flow
Abort done
NBUSYBK
UEIENX.
Endpoint
Endpoint
TXINE
Abort
Clear
reset
=0
Yes
No
Yes
KILLBK=1
KILLBK=1
No
Disable the TXINI interrupt.
Abort is based on the fact
that no banks are busy,
meaning that nothing has to
be sent.
Kill the last written
bank.
Wait for the end of the
procedure.
7766A–AVR–03/08