Nios® V Embedded Processor Design Handbook

ID 726952
Date 7/08/2024
Public
Document Table of Contents

6.2.3.4.1. Viewing Data

Captured Signal Tap data appears in the Data tab of the Signal Tap window. Every sample captured displays the following information:
Table 41.  Samples Captured Based on Nodes
Nodes Pipeline Stage Description Representation
*D_instr_pc[31..0] Instruction Decode (D) Program Counter Memory address of the instruction being fetched.
*D_instr_word[31..0] Instruction Word Fetched 32-bits instruction word.
*D_instr_valid Instruction Valid Valid instruction to continue E stage.
*E_instr_pc[31..0] Instruction Execute (E) Program Counter Memory address of the instruction being decoded.
*E_instr_word[6..0] Instruction Word 7-bits opcode from 32-bits instruction word.
*E_instr_valid Instruction Valid Valid instruction to continue M stage.
*M0_instr_pc[31..0] Memory (M) Program Counter Memory address of the instruction being executed.
*M0_instr_valid Instruction Valid Valid instruction to continue Write Back stage.

Using the Signal Tap tab controls, you can scroll through the program execution of the Nios® V processor. If the specified acquisition clock corresponds to the Nios® V processor clock, every rising clock edge corresponds to a new instruction cycle.

You may notice one or more empty instruction entries in the trace data gathered by the Signal Tap logic analyzer. These entries indicate that no instruction was executed by the Nios® V processor during that clock cycle. This behavior is typical, and can occur for the following reasons:

  • Cache Miss — The requested instruction address location generates a miss in the instruction cache, and additional clock cycles are required to fill the cache line and return the instruction.
  • Memory Contention or Speed — The instruction address location is in memory that requires multiple clock cycles to access, or in memory that is currently controlled by another peripheral or processor.

You can also view the trace data in the Signal Tap list file format. In this tabular format, the trace samples are displayed chronologically in rows. The list file format is useful because it is like the objdump file, simplifying the analysis process. Click File > Create/Update > Create Signal Tap List File to create the Signal Tap list file.