Gateware

Dexter Gateware

"Gateware" is what we call the FPGA programming that makes Dexter stunningly responsive. It allows feedback from encoder to motor in as little as 200 nanoseconds.

Dexters gateware configures the Xilinx Inc. XC7Z010-1CLG400C FPGA from the image of the micro SD card on the microzed board.

The SD card image has multiple partitions, one is the actual hard drive image when running in the robot. Another is the FAT partition which contains UBOOT, ZIMAGE, DTS (Device Tree) and the Gateware .BIT file. Those can be updated individually.

The DexRun.c firmware communicates with the gateware by setting memory mapped registers through the 'w' command oplet. They can be read via the 'r' oplet, and a standard set is returned in the status reply

The number of interfaces is the second highest byte in the first memory address plus 1, and the following addresses contain run length encoded type data expressing the size in bits of each memory mapped location.

The ultra fast response rate provided by the FPGA has several benefits:

1. We can run the P term in the PID controller up and not have oscillations. Actually since it’s integrated, and the time base is so fast, the P term is less than 1, but the point is that it tracks so close that in a slower system, it would oscillate. It doesn’t have time to overshoot. And that gives us better accuracy.

2. Small perturbations in the sensor system just get swamped by the good data around them. The mechanical system filters them out because it doesn’t have time to jerk. The motor inertia starts filtering mechanically at a few kHz, but If you get the update speed up over 50 kHz the motor inductance filters out the control signals as well.

3. The position of the motor is actually being dithered around the point it needs to be. We are stepping back and forth over points in between even the microstepping points. Especially on joints 4 and 5. This is where the inductive filtering helps us.

Mainly the group delay is so low that we don’t need any filtering.

Modes

Although they are made up of many different settings, we collect those together and tend to think of them as "modes" e.g.

Mode name	Description
Follow	The robot will move out of the way of any external force, actively driving the motors to avoid pressure. This allows you to move the robot as if it had no drive system
Keep	The robot will move it's motors to maintain the commanded position on each joint. This corrects for any deformation in the drive between the motor and the joint (e.g. belts) and always quickly returns the joint to the /exactly/ correct position.
Force Protect	A combination of Follow and Keep modes, this mode keeps the robot at it's commanded position unless it is hit, in which case, it will move out of the way of the strike and then slowly return.
Helping Hand	Helping hand is very similar to Follow Me mode. The difference is you can remove your hand and it won't fall over due to gravity. The key is the rate of force you apply (impulse). If you slowly apply a force the joints will stay locked and resist motion. This is the case when gravity is the primary applied force. If you quickly apply force like a quick shake or hit it will transition to a Follow Mode like state. To get out of the follow mode like state and maintain the position you moved it to you have to very gradually remove the force you are applying. Each joint works independently so some joints can be in Keep Mode while others are in Follow Mode. As always you must go to the original position to switch to other modes, this one is particularly unstable when switching to Keep and will require shutting off the robot if that is done by accident.

A Spreadsheet lists the modes and their exact settings. There are some variations on those modes as well. To develop a new mode, copy the sheet, edit, and then select your column and paste it into a make_ins file or convert it to a program.

Note that changing between modes can be problematic when the mode allows you to move the arm from the initial position, as is the case in follow or "helping hand" modes. You must return to the initial position before changing modes, and in those modes, you can not move the arm via the program. See Issue 3

Overview of the FPGA operation:

Keep Mode Detail

Tool Chain

Viva

Dexters gateware is written in Viva , a graphical system for defining logic. This (very) large picture shows the overview of that logic diagram: Dexter FPGA logic diagram overview

To install Viva,

• Download the Azido.msi installer and install the program on your system.
• Download the SystemDescriptions files for your target and copy them into a SystemDescriptions folder under the "Azido" install folder. e.g. C:\Program Files (x86)\Azido\SystemDescriptions (you may need administrative rights)
• Run VivaSD.exe, and on the System menu select "Open System" and select the .sd file for the desired system. For Dexter, it would be SystemDescriptions\OpalKelly\XEM6002\PMODBCSxAXIuZNObcs.sd file. This file contains the system descriptions for both the MicroZed board and the Opal Kelly XEM6002 FPGA board. This board can be used as an ICE for the MicroZed board. Other settings are required for the ICE capacity, including an environment variable called XIL_INSTALL=D:\Xilinx\14.6\ISE_DS\ISE\bin\nt. This is NOT required to use Viva for Dexters FPGA.
• Set Tools / Preferences as follows
  
• Add an Environment Variable called XIL_INSTALL which points to the Xilinx install folder and the \ISE_DS\ISE\bin\nt folder e.g. D:\Xilinx\14.6\ISE_DS\ISE\bin\nt (Click start, search for and select "Edit environment variables for your account".

Note: Viva was written in Borland C++ Builder. It can be compiled in Embarcadero C++ Builder 10.4 Pro, but we hope to find community support to port it to another C++ compiler e.g. gcc.

Xilinx ISC

To program the FPGA on Dexter, you will need to install the Xilinx ISC. We know the 14.6 version works. (14.7 probably works as well, we just haven't tested it.)
https://www.xilinx.com/support/download/index.html/content/xilinx/en/downloadNav/design-tools/archive.html

• Extract the Xilinx_ISE_DS_Win_14.6_P.68d_3.tar file to a folder.
• Run the xsetup.exe installer
• Accept the license terms.
• Select "ISE Webpack" for installation.
• Accept the default settings (you can change install location, but make sure it's off a root directory. E.g. D:\Xillinx is fine)
• Continue to setup the Visual C++ 2008 runtime system
• Continue to allow the device drivers to be installed

When the install finishes and the License Configuration Manager appears,

• select "Get free Vivado/ISE WebPack license".
• You will need to connect, and sign into Xilinx web site (create an account if you don't have one).
• Select "ISE WebPack license" and click "Generate Node-Locked License".
• Continue through the wizard and complete the license request.
• On the "Manage Licenses" screen, press the download arrow icon (lower left corner).
• Back in the License Configuration Manager, load the Xilinx.lic file and close.