RM0082
HS_USB 2.0 device
Doc ID 018672 Rev 1
479/844
23.5.2
OUT data memory structure
All endpoints that support out direction transactions (that is, endpoints receiving data from
the USB Host) must implement a memory structure according to the following
characteristics:
●
Each data buffer must have an associated descriptor which provides the status of the
buffer. Indeed, the buffer itself contains only raw data.
●
Each buffer descriptor is 4-quadlet length.
The out data memory structure is given in
reports the bits assignments
for out buffer status quadlet.
If the buffer status of the first descriptor is set to host ready (see BS field in
), the
DMA fetches and processes its data buffer. Otherwise, the DMA skips to the next descriptor
until it reaches the end of the descriptor chain.
Figure 47.
Out data memory
Data Descriptor Pointer
OUT Buffer Status Quadlet
Reserved
Buffer Pointer
Next Descriptor Pointer
Status Quadlet for
Non Iso-chronous OUT
R
RxBytes
BS
Rx Sts
15:0
26:16
29:28
31:30
0
31
L
27
Status Quadlet for
Iso-chronous OUT
Frame Number
RxBytes
BS
Rx Sts
13:0
26:16
29:28
31:30
L
27
PID
15:14