Cyclone IV NIOS

Introduction
Whilst building CycloneIV 8080 CPU I checked out a NIOS processor, in particular to determine how it used serial I/O.
Altera have provided NIOS as their ready-made processor for a number of years.  One reason for using FGPAs is to combine bespoke digital logic together with embedded uProc in the same chip and not many customers would want to build these features from scratch.[November 2019]

Overview
To specify hardware Altera provide Platform Designer so that you can choose components for you processor including a NIOS II core.  When you have working hardware software build tools (SBT) for Eclipse (IDE) enable you to specify, compile and download C Programs to the processor.
If you need extra functionality / peripherals you simply add the to the hardware design and utilise them in your program.

Samples
CycloneIV development kit came with some NIOS samples.  To check out the LED example I simply downloaded the SOF file and it ran.  Similarly for the Bell.  Unfortunately TFT examples didn't work directly.

Simple Processor
It is very easy to create a simple processor in Platform Designer.  The minimal components needed are a clock, somoe on-chip memory, a NIOS core and parallel IO for some LED outputs.  I wanted to add terminal I/O to the solution as I was researching that facility for my 8080 CPU and also being a bit fed up with using LEDs for debugging.
Using LEDs for output was easy but, try as I might I couldn't use JTAG USB as a serial port.  I feel that it may not be supported, or perhaps my USB blaster doesn't support that function.  Along the way I found it is much easier to debug NIOS problems using command in the NIOS2 shell

Once I used the DB9 serial port the process became a lot simpler.  Having tried a number of tutorials, mainly on youtube, my favourite was from Labbook pages. This helped me understand what we are creating at each step of the process.  

Useable Processor

The labbook processor included the C executable in its image. I used a youtube tutorial to create my useable processor which contained LEDs and serial I/O as well as the ability to load programs through Eclipse.

Extending Functionality

I could now add a Seven Segment display to my processor.  I chose to do this by specifying a 16-bit number to output from the CPU and then utilise previously written verilog to convert this to a number of hex digits and display them.  The display works by refreshing each digit in turn every millisecond so that all the digits appear to remain lit.  

I could have put this functionality in the NIOS processor and output 7SEG pin signals, but that was more work.