IMG_2382.JPGMicrontroller Programming

 

Our assignment was as follows:

†† - read an AVR data sheet

†† - add a button to the serial echo hello-world board

†† - modify the serial echo assembly program to respond to the button

†† - modify the serial echo C program to respond to the button

 

AVR Data Sheet

Since we were working with the ATtiny44 this week, I decided to read the data sheet for that chip.Itís 229 pages long!And itís very confusing.Iíve never worked with microcontrollers before, so this made me feel like I was drowning in a sea of bits and bytes without knowing which ones were helpful and which would turn my board into a pile of melted solder.At this point, it seemed almost helpless.

 

Attiny44_data_sheet.pdf

 

PCB Fabrication

I was very excited to make another PCB since I enjoyed it so much the first time.When deciding whether to add the button in cad.py or remaking the board in Eagle, I realized that the button was already described in the board and I would just have to add it in the correct place and add the traces.While Iíll probably use Eagle in the future, cad.py seemed like a good quick method for the problem at hand.I ended up having to download gedit though because both notepad and wordpad messed up the .cad files when I tried to edit them.Good ole MicrosoftÖ

 

Hello.echo.44.3.cad

 

hello.echo.44.3.PNG

 

I then used the Modela this time (as opposed to Max and Ilanís home brew machine from last time).The process was very streamlined and I was happy with how quickly I had my board.I then gathered all of the necessary components and went to work on stuffing my second board ever!

IMG_2379.JPGIMG_2380.JPG

 

I was very happy with both how quickly I was able to stuff the board and at how relatively nice the solder joints came out.No re-work done here!

 

Programming

This was definitely the most difficult part of the assignment.I started working with the .asm file and first went through the existing file to understand how it used the instruction set and registers from the data sheet.After I felt like I had a handle on that I tried to implement my button as an interrupt.I spent a long time trying to figure out how to set the correct bits to allow the interrupt and by the time I finally figured that out I realized that I had no idea how to catch the interrupt to have the chip do what I wanted!

 

I searched through Google extensively, but apparently nobody writes in .asm!While searching I decided that I was going to scrap the interrupt attempt and make the pin a standard input.I ended up getting that to work, but because the program sits in the loop waiting to receive a character from the keyboard, the button press didnít show a result unless I held the button down and pressed a key.While technically I completed the assignment because the button was doing something, I wasnít happy with it.I was determined to get the interrupt method to work.

 

I did finally found a way to direct the interrupt I wanted (PCINT0) to do what I wanted it to do (blink the LED and print ďButton status change!Ē on the screen).There isnít anywhere in the data sheet where I could have found it, so Iím glad I found it randomly online.Anyway, once I got the .asm file to work I moved on to the .c file.Everything went smoothly until once again I had trouble figuring out how to direct the PCINT0 interrupt to do what I wanted.Luckily, AVR Libc makes this much easier.I got it to work and was amazed at how much larger the .hex file was using .c (1530 bytes) instead of .asm (661 bytes).I guess I can see why .asm is useful (grudgingly).

 

My code is here:

Hello.echo.44.update.asm

Hello.echo.44.update.c

 

I used AVRStudio for my .asm programming and WINAvr for my .c programming.

 

IMG_2435.JPG

 

And it works!!!

 

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