Siemens C541U User Manual page 90

Another way to initiate buffer switching is setting bit DONE by software. This feature, which is shown
in figure 6-28 for USB read access, can be used to transfer a variable number of bytes. The
maximum number of bytes to be transferred is still determined by MaxLen, which is not changed
when bit DONE is set. The actual packet length (Len1 or Len2) is the number of bytes which have
been written to the buffer before bit DONE is set.
Number of
Data Bytes
MaxLen
Len1
Len2
CBF
= 0
MaxLen
Len1
Len2
UBF
= 0
SOF (n)
set
USB read accesses
Figure 6-28
Dual Buffer Mode USB Read Access : Buffer Switching by Setting Bit DONE
Semiconductor Group
DONE = 1
Page 0
1
Swap
Buffer
UBF = 1
Page 1
Frame n
On-Chip Peripheral Components
2
Page 1
SOF (n+1)
set
CPU write accesses
6-45
DONE = 1
3
Swap
Buffer
UBF = 1
Page 0
UBF = 0
Frame n+1
SOF (n+2)
set
C541U
Page 0
Time
Page 1
Time
MCT03408
1999-04-01