CC1110Fx / CC1111Fx
An isochronous data packet in the OUT FIFO
may have bit errors. The hardware will detect
this condition and set USBCSOL.DATA_ERROR.
Firmware should therefore always check this
bit when unloading a data packet.
The word size can be byte (8 bits) or word (16
bits). When word size transfer is used the
ENDIAN register must be set correctly (see
Section 12.5.7). The ENDIAN.USBRLE bit
selects whether a word is read as little or big
endian from the OUT FIFOs and the
ENDIAN.USBWLEbit selects whether a word is
written as little or big endian to the IN FIFOs.
Writing and reading words for the different
settings is shown in
The AutoClear feature will typically not be used
for isochronous endpoints since the packet
size will increase or decrease from frame to
frame.
Figure 45 and Figure 46 respectively. Notice
that the setting for these bits will be used for all
endpoints. Consequently, it is not possible to
have multiple DMA channels active at once
that use different endianness. The ENDIAN
register must be configured to use big endian
for both read and write for a word size transfer
to produce the same result as a byte size
transfer of an even number of bytes. Word size
transfers are slightly more efficient than byte
transfers.
12.16.7 DMA
DMA should be used to fill the IN endpoint
FIFOs and empty the OUT endpoint FIFOs.
Using DMA will improve the read/write
performance significantly compared to using
the 8051 CPU. It is therefore highly
recommended to use DMA unless timing is not
critical or only a few bytes are to be
transferred.
There are no DMA triggers for the USB
controller, meaning that DMA transfers must
be triggered by firmware.
Refer to Section 12.5 for more details
regarding DMA.
MSB LSB
ENDIAN.USBWLE = 0
SYNC
PID
MSB LSB MSB LSB
MSB LSB CRC16 EOP
To Host
MSB LSB
ENDIAN.USBWLE = 1
SYNC
PID
LSB MSB LSB MSB
LSB MSB CRC16 EOP
To Host
Figure 45: Writing Big/Little Endian
SYNC
PID
B0
B1
B2
B3
Bn-1 Bn
CRC16 EOP
From Host
ENDIAN.USBRLE = 0
ENDIAN.USBRLE = 1
B0
B1
B1
B0
Figure 46: Reading Big/Little Endian
SWRS033H
Page 177 of 246
TI [ TEXAS INSTRUMENTS ]
