1 This file specifies the format of USB packets used for in-band data
2 transmission and signaling on the USRP. All packets are 512-byte long,
3 and are transfered using USB "bulk" transfers.
5 IN packets are sent towards the host.
6 OUT packets are sent away from the host.
8 The layout is 32-bits wide. All data is transmitted in little-endian
12 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
13 |O|U|D|S|E| mbz | Chan | mbz | Tag | Payload Len |
14 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
16 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
24 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
31 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
34 mbz Must be Zero: these bits must be zero in both IN and OUT packets.
36 O Overrun Flag: set in an IN packet if an overrun condition was
37 detected. Must be zero in OUT packets. Overrun occurs when
38 the FPGA has data to transmit to the host and there is no
39 buffer space available. This generally indicates a problem on
40 the host. Either it is not keeping up, or it has configured
41 the FPGA to transmit data at a higher rate than the transport
44 U Underrun Flag: set in an IN packet if an underrun condition
45 was detected. Must be zero in OUT packets. Underrun occurs
46 when the FPGA runs out of samples, and it's not between
47 bursts. See the "End of Burst flag" below.
49 D Dropped Packet Flag: Set in an IN packet if the FPGA
50 discarded an OUT packet because its timestamp had already
53 S Start of Burst Flag: Set in an OUT packet if the data is the
54 first segment of what is logically a continuous burst of data.
55 Must be zero in IN packets.
57 E End of Burst Flag: Set in an OUT packet if the data is the
58 last segment of what is logically a continuous burst of data.
59 Must be zero in IN packets. Underruns are not reported
60 when the FPGA runs out of samples between bursts.
63 Chan 5-bit logical channel number. Channel number 0x1f is reserved
64 for control information. See "Control Channel" below. Other
65 channels are "data channels." Each data channel is logically
66 independent of the others. A data channel payload field
67 contains a sequence of homogeneous samples. The format of the
68 samples is determined by the configuration associated with the
69 given channel. It is often the case that the payload field
70 contains 32-bit complex samples, each containing 16-bit real
71 and imaginary components.
73 Tag 4-bit tag for matching IN packets with OUT packets.
74 [FIXME, write more...]
76 Payload Len: 9-bit field that specifies the length of the payload
77 field in bytes. Must be in the range 0 to 504 inclusive.
79 Timestamp: 32-bit timestamp. [FIXME, Write more]
80 On OUT packets, 0xffffffff means "Now".
82 Payload: Variable length field. Length is specified by the
85 Padding: This field is 504 - Payload Len bytes long, and its content
86 is unspecified. This field pads the packet out to a constant