CS194-126, Software De ned PCBs

CS194-126, Software Defined PCBsLecture 14: Embedded Debugging: System Bring-up

Richard ”Ducky” Lin

11 October 2016

1 Introduction

2 Demonstration

3 Summary

Ducky (UCB EECS) Embedded Debugging: System Bring-up 11 October 2016 1 / 16

Introduction

Introduction


Introduction

Goals

So, you have a great idea, and you just finished assembling your hardware.What now?

I Obviously, write firmware

But how to write it efficiently and well?I Efficiently writing code: write and test in small pieces

I If something breaks, narrow down culprits easilyI Make sure fundamentals are sane before building on top

I Writing good code: Thursday!


Introduction

Goals



But how to write it efficiently and well?

I Efficiently writing code: write and test in small piecesI If something breaks, narrow down culprits easilyI Make sure fundamentals are sane before building on top



Introduction

Goals



But how to write it efficiently and well?I Efficiently writing code: write and test in small pieces

I If something breaks, narrow down culprits easilyI Make sure fundamentals are sane before building on top



Introduction

Platform Introduction no demo like a live demo

EECS192 course project: line-following robot car

I Optical linescan camera, servo actuated steering

I Compute and control handled by microcontroller

I Lots of non-standard peripherals to bring up


Introduction

Platform Introduction no demo like a live demo

What would be a logical way to bring up this system?

I Write hardware drivers (encoder, camera, ...)

I Debug hardware drivers, in combination with hardware

I Write application logic (line detect, control loops, ...)


Demonstration

Sanity Check

What’s the first thing we should bring up?

Basic system test and debugging tools

I Classic embedded ”hello, world”: blinkingLEDs

I printf serial console

#include "mbed.h"

RawSerial serial(USBTX

, USBRX);

DigitalOut Led1(PTC8);

DigitalOut Led2(PTD0);

...

int main() {

}

you start here


Demonstration

Demonstration


Demonstration

Quad Encoder

A quad encoder uses two digital linesto count pulses with directionality(very common device)

How should we code this up?

I Find a library online, don’treinvent the wheel without a good reason

I Someone else has written it, andmany more people have tested it

mbed QEI API

Quad encoder waveforms


Demonstration

Make the clicky knob work!


Demonstration

Now bring up the servo!

you’ve already learned the servo PWM protocol


Demonstration

Line Camera

Many peripherals use standardinterfaces, like I2C and SPI

Some don’t, like this line camera

I Generally simple protocols

I Datasheet gives all the details

I Control integration time

I Pixel intensity on analog line

I Clock signal shifts out next pixel

TSL1401 Datasheet, page 5


Demonstration

Let’s write some code!


Demonstration

External ADC

A thermistor is connected to anexternal ADC, connected by I2C

So let’s bring up the ADC

I Datasheet describes protocol interms of I2C transactions

I Basically: write configurationregisters, read conversion result

ADS1015 Datasheet, page 8


Demonstration

I2C Fun Time!


Demonstration

Thermistors

MCP9701 is a linear activethermistor

I Voltage is proportional totemperature

I Details (offset and scaleconstants) in datasheet

I Around 20C, what is theexpected voltage?

I 0.8 V

I How would you code up theconversion from voltage totemperature?

MCP9701 Datasheet, pages 3 and 7


Demonstration

Closed-loop tracking fun demo

Bringing it all together


Summary

Summary

I Whirlwind tour of embedded system bring-up with custom peripheralsI A lot of artificial failures as examples of common failure modesI ... and a lot of details glossed over

I Write code incrementallyI Less things added, less things to question if something goes wrongI Verify each part before building on top of it

I When stuff goes wrong, get visibility into the systemI printf for software visibilityI Multimeter for non-time-varying quantities, like power railsI Oscilloscope for analog signalsI Logic analyzer for digital signals, with protocol analyzers

I Design for TestI Make system visibility easy, like with probe points


CS194-126, Software De ned PCBs

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