Jump to: navigation, search

Stream Protocol

1 Packet structure

The total packet size is 4096 bytes. A packet consists of two main parts: the header and the payload. The header contains receiver and transmitter status flags and the packet timestamp. The timestamp is a 64-bit samples counter used to synchronise received and transmitted signals. The counter is incremented with each sample after the receiver is enabled. The timestamp can be reset to 0 by using SMPL_NR_CLR bit; packet streaming should be disabled when resetting the timestamp. The payload contains RF sample data, the data format and ordering depending on the number of active channels and each sample's bit count.

1.1 Header structure

Byte Index Bits Description
0 15-12 Reserved
4 Disable timestamp synchronisation for this packet. Gets OR'ed with SPI_SYNCH_DIS.
0 - Synchronise packet transmission with timestamp (for transmitting only).
1 - Ignore timestamp, transmit as soon as possible. Prior synchronised packets existing in FIFO can delay transmission of unsynchronised packets.
3 TX packet dropped:
0 - TX is working normally.
1 - TX received packet with obsolete timestamp.
2-0 FPGA RX FIFO fill status:
0 - from 0% to 12.5%
1 - from 12.5% to 25%
2 - from 25% to 37.5%
3 - from 37.5% to 50%
4 - from 50% to 62.5%
5 - from 62.5% to 75%
6 - from 75% to 87.5%
7 - from 87.5% to 100%
1-7 15-0 Reserved
8-15 15-0 Timestamp: 64-bit sample counter, stored in Big Endian format.
When receiving: timestamp when the first sample in the payload was received.
When transmitting: timestamp when the first sample in the payload should be transmitted.

1.2 Payload structure

Byte Index Bits Description
16-3095 15-0 RF sample data: sample format and ordering depends on the Streaming configuration

2 Streaming configuration

The streaming configuration should be set before initiating data streaming. The protocol configuration is set by writing to board SPI registers. An address marked DNU means Do Not Use; the register bit is unsupported in the device.

2.1 Configuration registers

Address Default value Bits Name Description LimeSDR-USB 1v2
0x0000 15-0 Board ID 000E
0x0001 15-0 GW function 1
0x0002 15-0 GW revision
0x0003 00F0 15-8 Reserved
7-4 GW_TEST_RES Read-only, returns inverted bits from GW_TEST.
3-0 GW_TEST Vlue to test GW SPI.
0x0004 0000 15-0 PHASE_REG_SEL Value for phase shift in direct clocking mode.
0x0005 0000 15-0 DRCT_CLK_EN Each bit enables the clock to be a direct clock source: 1 - Enabled, 0 - Disabled.
[n] - nth clock
[1] - Second clock RX clk
[0] - First clock TX clk
0x0006 0000 15-11 Reserved
10 LOAD_PH_REG "1" loads phase shift value from PHASE_REG_SEL to phase shift module.
9-5 CNT_IND Clock counter selection
4-0 CLK_IND Clock selection 0 - TX clk, 1 - RX clk
0x0007 0003 15-0 CH_EN MIMO channel enable. Each bit means: 1 - Enabled, 0 - Disabled.
[n] - nth channel
[1] - Channel 1
[0] - Channel 0
0x0008 0102 15-11 Reserved
10 Reserved DNU
9 SYNCH_DIS Packet synchronisation using timestamps:
0 - Enabled
1 - Disabled
8 MIMO_INT_EN
7-2 Reserved
1-0 SMPL_WIDTH "10" - 12-bit
"01" - 14-bit
"00" - 16-bit
0x0009 0003 15-2 Reserved
1 TXPCT_LOSS_CLR Rising edge clears flag regarding RX packet dropping.
0 SMPL_NR_CLR Reset timestamp: RX and TX should be stopped when resetting.
1 -
0 - Normal operation
0x000A 0000 15-3 Reserved
2 STREAM_LOAD DNU
1 TX_EN
0 RX_EN

2.2 12-bit compressed samples

When using 12-bit compressed sample configuration, the packet payload has the following structure. Bytes are indexed from the start of the payload.

Byte index Bits Description
0 7-0 ch0_I0[7:0]
1 7-4 ch0_Q0[3:0]
3-0 ch0_I0[11:8]
2 7-0 ch0_Q0[11:4]
3 7-0 ch1_I1[7:0]
4 7-4 ch1_Q1[3:0]
3-0 ch1_I1[11:8]
5 7-0 ch1_Q1[11:4]
... ... ...

2.3 16-bit compressed samples

When using 16-bit compressed sample configuration, the packet payload has the following structure. Bytes are indexed from the start of the payload.

Byte index Bits Description
0 7-0 ch0_I0[7:0]
1 7-0 ch0_I0[15:8]
2 7-0 ch0_Q0[7:0]
3 7-0 ch0_Q0[15:0]
4 7-0 ch1_I1[7:0]
5 7-0 ch1_I1[15:8]
6 7-0 ch1_Q1[7:0]
7 7-0 ch1_Q1[15:8]
... ... ...

3 Document version

Based on Stream Protocol Datasheet, Version 05r00.

Changes since document generation:

  • Minor typographical and grammatical modifications.