Assembly Code from the Zynq 'C' Code

Introduction

For those who made the first steps in microprocessor's programming using assembly language, still today is nice to see what is assembly code generated from the 'C' code. On the other hand, sometimes it's necessary to write a specific very high speed routine using assembly language. 

The SDK tool in the Vivado (Xilinx) development suite, has a command line that execute a utility that generates the assembly code from the written 'C' code. 

Use of the Xilinx Microprocessor Debugger (XMD) Engine

The XMD is a tool that facilitates debugging programs and verifying systems using the Dual ARM Cortex-A9 (as well as the MicroBlaze and Power PC).

The SDK provides what is called an XMD console, where it is posible to type an XMD command using a Tool Command Language (Tcl) kind of language. 

The XMD console can be open in two different ways: 

1. When the Debug perspective is activated, the XMD console is automatically open. 
2. In the C/C++ perspective, do Xilinx Tool -> XMD Console.

An screenshot of the XMD console (in the Debug perspective)  is shows below. 

The XMD console is an standard Tcl console, where it is possible to run any available Tcl commands. The command should be typed following the XMD% prompt. 

Note: there is a more complete (and newer) tool that replaces XMD in some aspects: the Xilinx System Debugger Command-line Interface (XSDB). SDK also provides an XSDB console (this will be explained in a short future). However, there are some commands that are exclusively executed in the XMD console, such as the command we will see next. 

So, getting back to the point of this post, to be able to see the assembly language (and even the machine code) generated from the 'C' code, the XMD command line to type the following: 

arm-xilinx-eabi-objdump -S <complete_path_of_my_project_name>.elf

Here is the complete XMD command typed in the XMD console, no executed yet (note the doble back slash symbol):

The result of this XMD command it shows below, along with titles explaining each part of the file: 

If you browse the resultant file, you will see that is a huge file. But, it's easy to follow if you have some experience in assembly language. 

So, I hope you like this post, moreover, I hope it's somehow useful ! ...

Error (in some versions): "undefined reference to Xil_ICacheDisable"

Introduction

This problem happened to me more than a year ago, and I've been asked about it for several other colleagues, so I post it now.... l 

Trying of doing the simplest project ever in Vivado, using the ZedBaord, I run into a problem that made me feel very bad.... 

How can I get 10 error messages ? !? !?  from the 'Hello World' project !

Finding the Problem 

So, I followed all the steps that many of the on-line tutorials explains to build the hardware for the 'Hello World' project... here is my design: 

I did the necessary steps in Vivado to open the SDK environment. Then in the SDK, I created a new Application Project based in the Hello World template. 

When I executed Build Project for the simple Hello World project, I got the following errors: 

I did a search in the web, nothing related came out. So, I investigated on my side and I found out that there is a kind of 'bug' for this version of the Vivado, 2015.1, that even though the DDR interface is not configured in the hardware, it is generated incompletely in the software. 

Thinking on this simple project, there is no need for using the external DDR available in the ZedBoard. Therefore, there is no need for enabling the DDR controller from the Zynq configuration window. However, solve the problem that generates the error messages you do need to enable the DDR interface even though you don't do any read/write to the DDR. 

Important Note: other versions of Vivado do not generate these errors. 

Once you enable the DDR interface in the Vivado environment and go back to the SDK, create a new Hello World application project and then execute a Build Project.... no errors should be generated this time... 

Filtering Warning/Info Messages in ISE

Introduction 

After executing some of the available processes in the ISE environment, various and numerous messages are generated. These messages let the designer know the “health” of the project. In some cases, you may want to suppress a particular message from appearing in the “Errors and Warnings Report”. For example, you may get a Warning message about unconnected pins that you intend to be unconnected. ISE allows you to suppress, actually filter, a particular message from subsequent runs of the software. The tool you can use for this purpose is the “Message Filters”.

Messages That Can Be Filtered

Not all the message generated by the different processes can be filtered. You can filter messages that begin with "WARNING" or "INFO" and are followed by a library name and message number. For example, the following message can be filtered:

In this Warning message, Xst is the library name, and 2677 is the warning message number.

Note: ERROR messages cannot be filtered. Likewise, messages for some processes cannot be filtered (for example, messages generated by third-party software, such as the Synopsys software). Anyway, if you try to filter a message that cannot be filtered, a dialog box will come up stating that the message cannot be filtered.

Procedures to Filter Messages in ISE

1. Once you have your project open, enable message filtering as follows:
• Open the Design Summary pane by doing Project -> Design Summary/Reports.
• In the upper pane of the Design Summary, in the Design Overview, select Summary.
• In the button pane of the Design Summary, select Enable Message Filtering.
• 

• Note: it is also possible to enable message filtering from the project properties options available at: Project -> Design Properties in the Project Settings pane.

1. In the Processes pane of Project Navigator, run the process which generate the messages to be filtered. For instance execute the Synthesize-XST process.
2. In the Design Summary pane, and in the option Errors and Warnings, select the process that generate the messages to be filtered, for instance select Synthesis Messages to filter the messages generated by the synthesis tool. Then, in the main Project Navigator window all the Warnings, Infos and Errors messages related to the synthesis tool should be displayed
3. To select which messages should be filtered, in the pane listing all the messages highlight (left mouse click) the message to be filtered. If there are several messages of the same type, just select one. Then right-click on the message to filter, and select:
• Filter All Instances of This Message - to filter out all messages with the same library name and message number, regardless of the message text.
• Note: there is another options in the filtering menu:
• Filter This Instance Only - to filter out all messages with the same library name, message number, and text. This option is for just one message in particular, for instance for a specific bit of a bus.
4. Just to be sure the filter has been correctly setting up, do Edit -> Message Filters, a new window will come up in which the selected Warning/Info to be filtered will be detailed. 
• 
5. In this window you can:
• Remove the filter: right-click the filter and select Remove, or click the Remove filter(s) button.
• Temporarily disable a filter, right-click the filter and select Disable.
• Activate a disabled filter, right click the Enable.
6. Re-run the process generating the messages to be filtered. Then, from both the console as well as from the Error and Warning pane the messages should be filtered.

• 
  
7. Note: Still the filtered messages are available. Select All Implementation Messages under the Errors and Warnings option in the Design Summary pane. The filtered messages will be displayed with a Yes in the Filtered column.

Caution! 

When you suppress a message, it does not fix the issue. 

Do not filter messages for issues that must be fixed. 

Filter when you know what you are doing. Then, you can focus in warnings that you do need to fix.