usrp_helper

The usrp_helper block is used to set properties which are common to a sink and a source on the same USRP board, such as the firmware or USB Block Size. The block is mandatory for the usrp_sink and usrp_source block.

Description

This block can be placed anywhere into a Simulink model. Other blocks reference it by searching for blocks of type usrp_helper and comparing the parameter usrp_number against their own usrp_number. Parameters that control the operation of USRP boards are Firmware Filename, FPGA Bitstream Filename, USB Block Size and Number of USB Blocks. If this block is not found in a model the default values will be used for the parameters.

This block is a purely virtual block. If the Block Reduction option is enabled on the Optimization pane of the Configuration Parameters dialog box of a model, this block does not execute during simulation. Furthermore, this block does not add a single line of code to files generated by the Real Time Workshop.

Dialog Box

USRP Board Number

Specify on which USRP board this usrp_helper block acts upon. The first USRP board is numbered 0, the second 1 etc.

Serial Number

Informational message stating the USB serial number of the specified USRP board. Read only.

RX Daughterboards and TX Daughterboards

Informational messages stating the types of any daughterboards mounted on the USRP.

USB Block Size

Number of bytes that shall be transferred in one read or write operation across the USB bus. This must be a multiple of 512 bytes, since the USRP fragments large transfers in smaller ones of size 512.

The maximum depends on your operating system. To find it, enter inf for this parameter, the allowed maximum will then be displayed when you start the simulation.

A value of zero will make libusrp use its default value.

USB Number of Blocks

Number of asynchronous transfer operations of size USB Block Size that are started simultaneously. This means that a total of USB Number of Blocks times USB Block Size bytes are allocated in kernel space. Increasing this number can lead to less USRP over-/underruns, but at the same time leads to a higher latency.

A value of zero will make libusrp use its default value.

Firmware Filename

Filename of a compiled firmware for the Cypress EZ-USB FX2 USB Microcontroller. This file must stay inside the directory simulink-usrp/firmware/rev4/ in Intel Hex format.

If left empty, the default firmware std.ihx will be used. The firmware can be set using the Set Firmware block.

FPGA Bitstream Filename

Filename of a bitstream file for the FPGA on the USRP. This file must reside inside of the directory simulink-usrp/firmware/rev4/.

If left empty, the default bitstream std_2rxhb_2tx.rbf will be used. The bitstream can be set using the Set Bitstream block.

Sample Time Factor

Specifies that a sample time different than the "real" sampling time shall be reported to Simulink. By default, the sample time reflects the time between two frames coming out of a usrp_source or running into a usrp_sink. Thus, the absolute time displayed in Simulink during a simulation corresponds to real seconds, and Spectrum Scope blocks display the real bandwidth of a signal.

Changing this factor makes sense if counting samples is more natural to your application than counting time. E.g. specifing a Sample Time Factor of 64e6 makes Simulink display the number of samples calculated in the simulation.


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