Information

42.4.4 Buffer Descriptors (BDs)
A buffer descriptor provides endpoint buffer control information for the USB-FS and
processor. The Buffer Descriptors have different meaning based on whether it is the
USB-FS or processor reading the BD in memory.
The USB-FS 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 42-3. 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
Buffer Address (32-Bits)
Table 42-4. Buffer descriptor fields
Field Description
31–26
RSVD
Reserved
Table continues on the next page...
Chapter 42 Universal Serial Bus OTG Controller (USBOTG)
K20 Sub-Family Reference Manual, Rev. 1.1, Dec 2012
Freescale Semiconductor, Inc.
Preliminary
1035
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