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Table 33-5. Buffer descriptor fields (continued)
Field
Description
7
OWN
Determines whether the processor or USBFS currently owns the buffer. Except when KEEP=1, the
SIE hands ownership back to the processor after completing the token by clearing this bit.
This must always be the last byte of the BD that the processor updates when it initializes a BD.
0 The processor has access to the BD. USBFS ignores all other fields in the BD.
1 USBFS has access to the BD. While USBFS owns the BD, the processor should not modify any
other fields in the BD.
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 USBFS.
5
KEEP/
TOK_PID[3]
This bit has two functions:
• KEEP bit—When written by the processor, it serves as the KEEP bit. 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 Allows USBFS to release the BD when a token has been processed.
1 This bit is unchanged by USBFS. Bit 3 of the current token PID is written back to the BD by
USBFS.
• TOK_PID[3]—If the OWN bit is also set, the BD remains owned by USBFS indefinitely; when
written by USB, it serves as the TOK_PID[3] bit.
0 or 1 Bit 3 of the current token PID is written back to the BD by USBFS.
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.
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 USBFS writes bit 2 of the current token PID to the BD.
1 This bit is unchanged by USBFS.
3
DTS/
TOK_PID[1]
Setting this bit enables USBFS 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 USBFS.
0 Data Toggle Synchronization is disabled.
1 Enables USBFS to perform Data Toggle Synchronization.
2
BDT_STALL
TOK_PID[0]
Setting this bit causes USBFS 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 USBFS.
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
KL27 Sub-Family Reference Manual , Rev. 5, 01/2016
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Freescale Semiconductor, Inc.