NXP Semiconductors K22F series - Buffer Descriptors (Bds)

Table 43-3. BDT address calculation fields (continued)
Field Description
ODD Maintained within the USBFS SIE. It corresponds to the buffer currently in use. The buffers are used
in a ping-pong fashion.
43.3.4 Buffer Descriptors (BDs)
A buffer descriptor provides endpoint buffer control information for USBFS and the
processor. The Buffer Descriptors have different meaning based on whether it is USBFS
or the processor reading the BD in memory.
The USBFS Controller uses the data stored in the BDs to determine:
• Who owns the buffer in system memory
• Data0 or Data1 PID
• Whether to release ownership upon packet completion
• No address increment (FIFO mode)
• Whether data toggle synchronization is enabled
• How much data is to be transmitted or received
• Where the buffer resides in system memory
While the processor uses the data stored in the BDs to determine:
• Who owns the buffer in system memory
• Data0 or Data1 PID
• The received TOKEN PID
• How much data was transmitted or received
• Where the buffer resides in system memory
The format for the BD is shown in the following figure.
Table 43-4. Buffer descriptor format
31:26 25:16 15:8 7 6 5 4 3 2 1 0
RSVD
BC
(10 bits)
RSVD OWN DATA0/1
KEEP/
TOK_PID[3]
NINC/
TOK_PID[2]
DTS/
TOK_PID[1]
BDT_STALL/
TOK_PID[0]
0 0
Table continues on the next page...
Programmers interface
K22F Sub-Family Reference Manual, Rev. 4, 08/2016
1078 NXP Semiconductors