Lantronix DSTni-EX manual 6. USB Buffer Descriptor Format Definitions, BD Owner, USB Ownership

Table 4-6. USB Buffer Descriptor Format Definitions

Bits	Field Name	Description
7	OWN	BD Owner
		Specifies which unit has exclusive access to the BD.
		0 = microprocessor has exclusive and entire BD access; USB ignores all other
		fields in the BD
		1 = USB has exclusive BD access SIE writes a 0 to this bit when it completes a
		token, except when KEEP=1. This byte must always be the last byte the
		microprocessor updates when it initializes a BD. After the BD is assigned to the
		USB, the microprocessor must not change it.
6	DATA0/1	DATA0/1 Transmit or Receive
		Transmission or reception of a DATA0 or DATA1 field.
		0 = transmission or reception of a DATA0 field.
		1 = transmission or reception of a DATA1 field.
		The USB does not change this value.
5	USB_OWN	USB Ownership
		1 = once the OWN bit is set, the USB owns it forever.
		0 = USB can release the BD when a token is processed.
		Typically, this bit is set to 1 with ISO endpoints that feed a FIFO. The
		microprocessor is not informed of the token processing. Instead, the process is
		a simple data transfer to or from the FIFO.
		When this bit is set to1:
		• The NINC bit is usually set to prevent the address from incrementing.
		• The USB does not change this bit; otherwise the USB writes bit 3 of the
		current token PID back to the BD.
4	NINC	No Increment Bit
		Disables DMA engine address incrementation, forcing the DMA engine to read
		or write from the same address. This is useful for endpoints when data must be
		read from or written to a single location such as a FIFO. Typically, this bit is set
		with the USB_OWN bit for ISO endpoints that interface with a FIFO. If
		USB_OWN=1, the USB does not change this bit; otherwise, the USB writes bit
		2 of the current token PID to the BD.
3	DTS	Data Toggle Synchronization
		0 = USB cannot perform Data Toggle Synchronization.
		1 = USB can perform Data Toggle Synchronization.
		If USB_OWN=1, the USB does not change this bit; otherwise, the USB writes
		bit 1 of the current token PID to the BD.
1:0	BCH[9:8]	Byte Count High Bits
		Represent the high-order bits of the 10-bit byte count. The USB SIE changes
		this field after completing an RX transfer with the byte count of the data
		received.
7:0	BCL	Byte Count Low Bits
		Represent the low-order byte of the 10-bit byte count. BCH and BCL together
		form the 10-bit byte count. This represents the number of bytes to transmit for
		a TX transfer or receive during an RX transfer. Valid byte counts are 0 to 1023.
		The USB SIE changes this field after completing an RX transfer with the actual
		byte count of the data received.
7:0	ADDR[31:0]	Address Bits
(Bytes 4		Represent the 32-bit buffer address in system memory. DSTni only uses the
through 2 and		lower 24 bits to form the address where the buffer resides in system memory.
Low Byte)		This is the address that the USB DMA engine uses when it reads or writes
		data. The USB does not change these bits.

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