Information

Table 40-4. Buffer descriptor fields (continued)
Field Description
7
OWN
Determines whether the processor or the USB-FS currently owns the buffer. Except when
KEEP=1, the SIE writes a 0 to this bit when it has completed a token.
This must always be the last byte of the BD that the processor updates when it initializes a BD.
0 The processor has exclusive access to the BD. The USB-FS ignores all other fields in the BD.
1 USB-FS has exclusive access to the BD. After the BD has been assigned to the USB-FS, the
processor should not change it in any way.
6
DATA0/1
Defines whether a DATA0 field (DATA0/1=0) or a DATA1 (DATA0/1=1) field was transmitted or
received. It is unchanged by the USB-FS.
5
KEEP/
TOK_PID[3]
Typically, this bit is 1 with ISO endpoints feeding a FIFO. The microprocessor is not informed that
a token has been processed, the data is simply transferred to or from the FIFO. When KEEP is
set, normally the NINC bit is also set to prevent address increment.
0 Bit 3 of the current token PID is written back to the BD by the USB-FS. Allows the USB-FS to
release the BD when a token has been processed.
1 This bit is unchanged by the USB-FS. If the OWN bit also is set, the BD remains owned by the
USB-FS forever.
4
NINC/
TOK_PID[2]
No Increment (NINC)
Disables the DMA engine address increment. This forces the DMA engine to read or write from the
same address. This is useful for endpoints when data needs to be read from or written to a single
location such as a FIFO. Typically this bit is set with the KEEP bit for ISO endpoints that are
interfacing to a FIFO.
0 The USB-FS writes bit 2 of the current token PID to the BD.
1 This bit is unchanged by the USB-FS.
3
DTS/
TOK_PID[1]
Setting this bit enables the USB-FS to perform Data Toggle Synchronization.
• If KEEP=0, bit 1 of the current token PID is written back to the BD.
• If KEEP=1, this bit is unchanged by the USB-FS.
0 Data Toggle Synchronization is disabled.
1 Enables the USB-FS to perform Data Toggle Synchronization.
2
BDT_STALL
TOK_PID[0]
Setting this bit causes the USB-FS to issue a STALL handshake if a token is received by the SIE
that would use the BDT in this location. The BDT is not consumed by the SIE (the owns bit
remains set and the rest of the BDT is unchanged) when a BDT-STALL bit is set.
• If KEEP=0, bit 0 of the current token PID is written back to the BD.
• If KEEP=1, this bit is unchanged by the USB-FS.
0 No stall issued.
1 The BDT is not consumed by the SIE (the OWN bit remains set and the rest of the BDT is
unchanged).
Table continues on the next page...
Programmers interface
K20 Sub-Family Reference Manual, Rev. 2, Feb 2012
888 Freescale Semiconductor, Inc.