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| -rw-r--r-- | usrp/doc/inband-signaling-usb | 83 |
1 files changed, 83 insertions, 0 deletions
diff --git a/usrp/doc/inband-signaling-usb b/usrp/doc/inband-signaling-usb new file mode 100644 index 000000000..420ba753e --- /dev/null +++ b/usrp/doc/inband-signaling-usb @@ -0,0 +1,83 @@ +This file specifies the format of USB packets used for in-band data +transmission and signaling on the USRP. All packets are 512-byte long, +and are transfered using USB "bulk" transfers. + +IN packets are sent towards the host. +OUT packets are sent away from the host. + +The layout is 32-bits wide. All data is transmitted in little-endian +format across the USB. + + + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + |O|U|E|D| mbz | Chan | mbz | Tag | Payload Len | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Timestamp | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | + + + + | Payload | + . . + . . + . . + | | + + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | ... | . + +-+-+-+-+-+-+-+ . + . . + . Padding . + . . + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + + mbz Must be Zero: these bits must be zero in both IN and OUT packets. + + O Overrun Flag: set in an IN packet if an overrun condition was + detected. Must be zero in OUT packets. Overrun occurs when + the FPGA has data to transmit to the host and there is no + buffer space available. This generally indicates a problem on + the host. Either it is not keeping up, or it has configured + the FPGA to transmit data at a higher rate than the transport + (USB) can support. + + U Underrun Flag: set in an IN packet if an underrun condition + was detected. Must be zero in OUT packets. Underrun occurs + when the FPGA runs out of samples, and it's not between + bursts. See the "End of Burst flag" below. + + E End of Burst Flag: Set in an OUT packet if the data is the + last segment of what is logically a continuous burst of data. + Must be zero in IN packets. Underruns are not reported + when the FPGA runs out of samples between bursts. + + D Dropped Packet Flag: Set in an IN packet if the FPGA + discarded an OUT packet because its timestamp had already + passed. + + Chan 5-bit logical channel number. Channel number 0x1f is reserved + for control information. See "Control Channel" below. Other + channels are "data channels." Each data channel is logically + independent of the others. A data channel payload field + contains a sequence of homogeneous samples. The format of the + samples is determined by the configuration associated with the + given channel. It is often the case that the payload field + contains 32-bit complex samples, each containing 16-bit real + and imaginary components. + + Tag 4-bit tag for matching IN packets with OUT packets. + [FIXME, write more...] + + Payload Len: 9-bit field that specifies the length of the payload + field in bytes. Must be in the range 0 to 504 inclusive. + + Timestamp: 32-bit timestamp. [FIXME, Write more] + On OUT packets, 0xffffffff means "Now". + + Payload: Variable length field. Length is specified by the + Payload Len field. + + Padding: This field is 504 - Payload Len bytes long, and its content + is unspecified. This field pads the packet out to a constant + 512 bytes. + |