Slides created by: Professor Ian G. Harris Test and Debugging  Controllability and observability are required Controllability Ability to control sources of data used by the system Input pins, input interfaces (serial, ethernet, etc.) Registers and internal memory Observability Ability to observe intermediate and final results Output pins, output interfaces Registers and internal memory

Slides created by: Professor Ian G. Harris I/O Access is Insufficient  Control and observation of I/O is not enough to debug main(){ x = f1(RA0,RA1); foo (x); } foo(x){ y = f2(x); bar (y); } bar(y){ RA2 = f3(y); } RA0 RA1 RA2  If RA2 is incorrect, how do you locate the bug?  Control/observe x and y at function calls?

Slides created by: Professor Ian G. Harris Embedded Debugging Properties of a debugging environment: 1. Run Control of the target - Start and stop the program execution 2. Ability to change code and data on target - Fix errors, test alternatives 3. Real-Time Monitoring of target execution - Non-intrusive in terms of performance 4. Timing and Functional Accuracy - Debugged system should act like the real system

Slides created by: Professor Ian G. Harris Host-Based Debugging  Compile and debug your program on the host system, not target - Compile C to your laptop, not the microcontroller Advantages: 1.Can use a good debugging environment 2.Easy to try it, not much setup (register names, etc) Disadvantages: 1.Timing is way off 2.Peripherals will not work, need to simulate them 3.Interrupts probably implemented differently 4.Different data sizes and “endian”ness

Slides created by: Professor Ian G. Harris Instruction Set Simulator  Instruction Set Simulator (ISS) runs on the host but simulates the target  Each machine instruction on the target is converted into a set of instructions on the host  Example:  Target Instruction - add x : Adds register x to the acc register, result in the acc register  Host equivalent: add acc, x, acc : Adds second reg to third, result in the first reg

Slides created by: Professor Ian G. Harris ISS Tradeoffs Advantages: 1. Total run control 2. Can change code and data easily Disadvantages: 1. Simulator assumptions can cause inaccuracies 2. Timing is off, no real-time monitoring - initial register values, timing assumptions 3. “Hardware environment” of target cannot be easily modeled

Slides created by: Professor Ian G. Harris Hardware Environment RAM PIC RA0 RA1 RA2  PIC communicates with the switch and the RAM  Communications must be modeled to test PIC code  Simulators allow generation of simple event sequences  Responsiveness is more difficult to model

Slides created by: Professor Ian G. Harris Remote Debug/Debug Kernel  Remote debugger on the host interacts with a debug kernel on the target  Communication through a spare channel (serial or ethernet)  Debug kernel responds to commands from remote debugger  Debug kernel is an interrupt, so control is possible at any time Host (PC) Target (PIC) Serial or Ethernet

Slides created by: Professor Ian G. Harris Remote Debug Tradeoffs Advantages: 1.Good run control using interrupts to stop execution 2.Debug kernel can alter memory and registers 3.Perfect functional accuracy Disadvantages: 1.Debug interrupts alter timing so real-time monitoring is not possible 2.Need a spare communication channel 3.Need program in RAM (not flash) to add breakpoints

Slides created by: Professor Ian G. Harris ROM Emulator RAM ucontroller Target ucontroller Host Instructions Serial or ethernet Target ucontroller ROM Instructions  Common to read instructions from a separate ROM on the target  ROM emulator substitutes the ROM for a RAM with a controller

Slides created by: Professor Ian G. Harris ROM Emulator Features  Remote debugger where ROM is replaced by RAM - Debug kernel is in the RAM  Solves the “non-writable ROM” problem of remote debugging  ROM emulator completely controls the instructions - Full data access is possible  ROM emulator can contain a debug communication channel No need for a spare channel

Slides created by: Professor Ian G. Harris ROM Emulator Disadvantages  Instruction ROM must be separate from the microcontroller - No embedded ROM  There must be a way to write to the ROM - May be done with a complex sequence of reads  Alters timing, just as any debug kernel would

Slides created by: Professor Ian G. Harris In-Circuit Emulation (ICE) Target ucontroller ROM Instructions  Replace the microcontroller with an new one  Can select instructions from external ROM (normal mode) or internal shadow RAM (test mode) Shadow RAM Target ucontroller Mux ROM Host

Slides created by: Professor Ian G. Harris ICE Advantages  ICE can always maintain control of the program  - Interrupt cannot be masked  Works even if system ROM is broken  Generally the best solution