Baseband Buffers Module Implementation

The WARPLab Reference Design implements a Baseband module that buffers incoming and outgoing samples from radio interfaces. It supports up to 4 interfaces, including both I/Q and RSSI. On WARP v3 hardware, each buffer is 2¹⁵ samples long. On WARP v2 hardware, each buffer is 2¹⁴ samples long.

Related Components:

• MATLAB:
  • wl_baseband_buffers​ class
• WARP Hardware:
  • warplab_buffers peripheral
  • warplab_agc peripheral
  • wl_baseband​ C software

Baseband Commands

Baseband commands are selected as string inputs to the wl_basebandCmd method in wl_node.m​. These strings are each individual cases of the switch statement in procCmd method of wl_baseband_buffers.m​.

Syntax

MATLAB allows two valid forms of syntax for calling methods

• Let N be a scalar or vector of wl_node objects
• Let command_string be a string containing a particular command
• Let arg be an argument for that command (optional)

Syntax 1: wl_basebandCmd(N, command_string, arg1, arg2, ..., argN)

Syntax 2: N.wl_basebandCmd(command_string, arg1, arg2, ..., argN)

These two different forms of syntax are identical and either may be used for issuing commands to WARP nodes.

Optional Buffer Selection Syntax

Some baseband commands require the selection of one or more buffers. This requirement is specified in the below documentation with Requires BUFF_SEL:. If a command requires a buffer selection, then the following syntaxes are valid:

• Let buffer_selection be a collection of interfaces or the string 'RF_ALL'

Syntax 1: wl_interfaceCmd(N, buffer_selection, command_string, arg1, arg2, ..., argN)

Syntax 2: N.wl_interfaceCmd(buffer_selection, command_string, arg1, arg2, ..., argN)

Command List and Documentation

tx_delay

Transmit delay- gets or sets the number of sample periods the baseband waits between the trigger and starting the transmission

Requires BUFF_SEL: No

Arguments: none or (uint32 TX_DLY)

Returns: (uint32 TX_DLY) or none

If an argument is specified, this command enters a write mode where that argument is written to the board. If no argument is specified, the current value of TX_DLY is read from the board.

tx_length

Transmit length- sets the duration of each transmit cycle, in sample periods

Requires BUFF_SEL: No

Arguments: (uint32 TX_LEN)

Returns: none

NOTE: This will error if the user tries to read tx_length from the board. the 'tx_buff_max_num_samples' command should be used to determine the capabilities of the board.

rx_length

Receive length- reads or sets the duration of each receive cycle, in sample periods

Requires BUFF_SEL: No

Arguments: (uint32 RX_LEN)

Returns: none

NOTE: This will error if the user tries to read tx_length from the board. the 'tx_buff_max_num_samples' command should be used to determine the capabilities of the board.

tx_buff_max_num_samples

Maximum number of TX samples

Requires BUFF_SEL: Yes (Vector notation [RFA, RFB])

Arguments: none

Returns: (uint32 MAX_TX_LEN)

rx_buff_max_num_samples

Maximum number of RX samples

Requires BUFF_SEL: Yes (Vector notation [RFA, RFB])

Arguments: none

Returns: (uint32 MAX_RX_LEN)

continuous_tx

Enable/disable continuous transmit mode

Requires BUFF_SEL: No

Arguments: (boolean CONT_TX) CONT_TX:
true enables continuous transmit mode
false disable continuous transmit mode

Returns: none

Restrictions on continuous transmit waveform length:

WARPLab 7.5.0 and higher:

0 to 2^15   --> Waveform will be transmitted for the exact number of samples
   > 2^15   --> Waveform must be a multiple of 2^14 samples for the waveform
                to be transmitted exactly.  Otherwise, waveform will be appended 
                with whatever IQ data is in the transmit buffer to align the 
                waveform to be a multiple of 2^14 samples.

NOTE: In WARPLab 7.5.x, it is an error to perform a Read IQ while in continuous transmit mode.

WARPLab 7.4.0 and prior:

0 to 2^15   --> Waveform will be transmitted for the exact number of samples
   > 2^15   --> Not supported

tx_buff_en

Enable transmit buffer for one or more interfaces. When a buffer is enabled it will drive samples into its associated interface when a trigger is received. The interface itself must also be enabled (wl_interfaceCmd(...,'tx_en')) to actually transmit the samples

Requires BUFF_SEL: Yes (Scalar notation [RFA + RFB])

Arguments: none

Returns: none

rx_buff_en

Enable receive buffer for one or more interfaces. When a buffer is enabled it will capture samples from its associated interface when a trigger is received. The interface itself must also be enabled (wl_interfaceCmd(...,'rx_en'))

Requires BUFF_SEL: Yes (Scalar notation [RFA + RFB])

Arguments: none

Returns: none

tx_rx_buff_dis

Disable the Tx and Rx buffers for one or more interfaces. When a buffer is disabled it will not output/capture samples when a trigger is received, even if the associated interface is enabled

Requires BUFF_SEL: Yes (Scalar notation [RFA + RFB])

Arguments: none

Returns: none

read_buff_state

Read the current state of the buffer

Requires BUFF_SEL: Yes (Vector notation [RFA, RFB])

Arguments: none

Returns: Current state of the buffer: TX, RX or STANDBY

tx_buff_clk_freq

Read the transmit sample clock frequency out of the buffer core.

Requires BUFF_SEL: No

Arguments: none

Returns: (uint32 Fs_Tx) Fs_Tx: Tx sample frequency of buffer core in Hz

rx_buff_clk_freq

Read the receive sample clock frequency out of the buffer core.

Requires BUFF_SEL: No

Arguments: none

Returns: (uint32 Fs_Rx) Fs_Rx: Rx sample frequency of buffer core in Hz

rx_rssi_clk_freq

Read the receive RSSI sample clock frequency out of the buffer core.

Requires BUFF_SEL: No

Arguments: none

Returns: (uint32 Fs_RxRSSI) Fs_RxRSSI: Rx RSSI sample frequency of buffer core in Hz

write_iq

Write I/Q samples to the specified buffers. The dimensions of the buffer selection and samples matrix must agree. The same samples can be written to multiple buffers by combining buffer IDs

Requires BUFF_SEL: Yes (combined BUFF_SEL values ok)

Arguments: (complex double TX_SAMPS, int OFFSET) TX_SAMPS: matrix of complex samples. The number of columns must match the length of BUFF_SEL OFFSET: buffer index of first sample to write (optional; defaults to 0)

Examples:

TxLength = 2^14;
Ts = 1/(wl_basebandCmd(node0,'tx_buff_clk_freq'));
t  = ![0:Ts:(TxLength-1)*Ts].';                      % column vector
X  = exp(t*1i*2*pi*3e6);                             % 3MHz sinusoid
Y  = exp(t*1i*2*pi*5e6);                             % 5MHz sinusoid

% Write X to RFA
wl_basebandCmd(node, RFA, 'write_IQ', X);

% Write X to RFA and RFB
wl_basebandCmd(node, (RFA + RFB), 'write_IQ', X);

% Write X to RFA, Y to RFB
wl_basebandCmd(node, ![RFA RFB], 'write_IQ', ![X Y]);

write_iq_checksum

Write IQ checksum - gets the current Write IQ checksum from the node.

Requires BUFF_SEL: No

Arguments: none

Returns: (uint32 WRITE_IQ_CHECKSUM)

read_iq

Read I/Q samples from the specified buffers. The elements of the buffer selection must be scalers which identify a single buffer. To read multiple buffers in one call, pass a vector of individual buffer IDs

Requires BUFF_SEL: Yes (combined BUFF_SEL values not allowed)

Arguments: (int OFFSET, int NUM_SAMPS) OFFSET: buffer index of first sample to read (optional; defaults to 0)
NUM_SAMPS: number of complex samples to read (optional; defaults to length(OFFSET:rxIQLen-1))[[BR]]

Examples:

% Read full buffer for RFA
%     NOTE:  size(X) will be ![rxIQLen, 1]
X = wl_basebandCmd(node, RFA, 'read_IQ');

% Read partial buffer for RFA (samples 1000:4999)
%     NOTE:  size(X) will be ![5000, 1]
X = wl_basebandCmd(node, RFA, 'read_IQ', 1000, 5000);

% Read full buffers for RFA and RFB
%     NOTE:  size(X) will be ![rxIQLen, 2]
X = wl_basebandCmd(node, ![RFA RFB], 'read_IQ');

read_rssi

Read RSSI samples from the specified buffers. The elements of the buffer selection must be scalers which identify a single buffer. To read multiple buffers in one call, pass a vector of individual buffer IDs.

See 'read_iq' for arguments/returns

get_tx_count

For the given buffers, get the number of times the TX state machine has run

Requires BUFF_SEL: Yes (Vector notation [RFA, RFB])

Arguments: none

Returns: [uint32 BUFFER_COUNTER]

get_rx_count

For the given buffers, get the number of times the RX state machine has run

Requires BUFF_SEL: Yes (Vector notation [RFA, RFB])

Arguments: none

Returns: [uint32 BUFFER_COUNTER]

reset_tx_count

For the given buffers, reset the counter that records the number of times the TX state machine has run

Requires BUFF_SEL: Yes (Vector notation [RFA, RFB])

Arguments: none

Returns: [uint32 BUFFER_COUNTER]

reset_rx_count

For the given buffers, reset the counter that records the number of times the RX state machine has run

Requires BUFF_SEL: Yes (Vector notation [RFA, RFB])

Arguments: none

Returns: [uint32 BUFFER_COUNTER]

agc_state

Read AGC state from the specified buffers. The elements of the buffer selection must be scalers which identify a single buffer. To read multiple buffers in one call, pass a vector of individual buffer IDs

Requires BUFF_SEL: Yes (Vector notation [RFA, RFB])

Arguments: none

Returns: agc_state -- column vector per buffer BUFF_SEL agc_state(1): RF gain chosen by AGC
agc_state(2): BB gain chosen by AGC
agc_state(3): RSSI observed by AGC at time of lock

agc_thresh

Read or write AGC threshold.

agc_target

Set the AGC target

Requires BUFF_SEL: No. Values apply to all RF paths

Arguments: (int32 target) target: target receive power (in dBm)
default value: -16

Returns: none

This command is the best way to tweak AGC behavior to apply more or less gain. For example, a target of -5dBm will apply more gain thatn a target of -10dBm, so the waveform will be larger at the inputs of the I and Q ADCs.

agc_dco

Enable/disable DC offset correction

Requires BUFF_SEL: No

Arguments: (boolean DCO) DCO:
true enables DC offset correction
false disable DC offset correction

Returns: none

agc_done_addr

Sample index where AGC finished

Requires BUFF_SEL: No. Values apply to all RF paths

Arguments:

Returns: (uint32) sample_index

agc_reset

Resets the AGC to its default state

Requires BUFF_SEL: No. Values apply to all RF paths

Arguments: none

Returns: none

agc_reset_per_rx

Get / Set whether the AGC will reset on per RX or hold gains across RX

Arguments: 'true' or 'false'; none on read

Returns: none on write; 'true' or 'false'

agc_config

Set the configuration of the AGC

This function will set the following AGC configuration fields:

• RSSI averaging length
• Voltage DB Adjust
• Initial BB Gain

Requires BUFF_SEL: No

Arguments:

• RSSI Averaging length (Integer value in [0, 3])
  
• Voltage DB Adjust (Integer value in [0, 63])
  
• Initial BB Gain (RX) (Integer value in [0, 31])
  

Returns : None

agc_iir_hpf

Set the Infinite Impulse Response (IIR) High Pass Filter (HPF) coefficients

This function will set the following IIR HPF coefficients:

• A1
• B0

NOTE: By default the reference design uses a filter with a 3 dB cutoff at 20 kHz with 40 MHz sampling. This results in coefficients:

• A1 = -0.996863331833438
  
• B0 = 0.99843166591671906
  

Requires BUFF_SEL: No

Arguments:

• A1 coefficient (Value in [-1, 1]; range represented by Fix_18_17)
  
• B0 coefficient (Value in [0, 2]; range represented by UFix_18_17)
  

Returns : None

agc_rf_gain_threshold

Set the RF gain thresholds

This function will set the following fields:

• 3 -> 2 RF gain threshold
• 2 -> 1 RF gain threshold

After the AGC has converted RSSI to power (dBm), this will select the the thresholds used to set the RF (LNA) gain in the MAX2829.

Requires BUFF_SEL: No

Arguments:

• 3 -> 2 RF gain threshold (Integer value in [-128, 127])
  
• 2 -> 1 RF gain threshold (Integer value in [-128, 127])
  

Returns : None

agc_timing

Set the AGC timing

This function will set the following fields:

• Sample to take first RSSI capture
• Sample to take second RSSI capture
• Sample to take the Voltage DB capture
• Sample to complete the AGC

Requires BUFF_SEL: No

Arguments:

• Capture RSSI 1 (Integer value in [0, 255])
  
• Capture RSSI 2 (Integer value in [0, 255])
  
• Capture Voltage DB (Integer value in [0, 255])
  
• AGC Done (Integer value in [0, 255])
  

Returns : None

agc_dco_timing

Set the AGC DC Offset (DCO) timing

This function will set the following fields:

• Sample to start the DCO
• Sample to start the IIR HPF

Requires BUFF_SEL: No

Arguments:

• Start DCO (Integer value in [0, 255])
  
• Start IIR HPF (Integer value in [0, 255])
  

Returns : None