Changes

From the File Great --> Open menu, select Open Object File For Debugging: [[File:sim1_openobjectnow let's look into how we can simulate this project.png]]

# On the tool-bar, there is an open to select the debug interface. It may say "No Tool" as below, if so click to select the tool: [[File:sim2_selectelfsim7_selecttoolA.png]] # And select the "Simulator" option: [[File:sim3_saveprojectsim8_selecttoolB.png]] [[File:sim4_selectxmega# You're ready to simulate! As a first example, you can set Breakpoints by clicking in the margin.png]] [[FileIf they can be set a red circle will appear. Be very careful in location - sometimes once you go to simulate the breakpoints will be disabled or moved (more on this later), so you'll have to go back and check the location of them once the simulator is running:sim5_openfile.png]]  [[File:sim6_setbreakpoint.png]] # To start the simulator, select the "Start Debugging" option: [[File:sim7_selecttoolAsim9_startdebug.png]] [[File:sim8_selecttoolB# But what happens? You'll likely see NO break-point hit! This is because the code is waiting on the serial port.png]] [[FileGo back to the source-file and add a call to the AES encryption operation, just as it would be called later. The following shows the location to add this to in the <code>simpleserial-aes.c</code> file:sim9_startdebug.png]]  [[File:sim10_insertcall.png]] # Recompile. Atmel Studio should flag the object file as changed (NB: only if using external project, if building through Atmel Studio these messages don't appear), if so hit "Reload": [[File:sim11_reload1.png]]  [[File:sim11_reload2.png]] # You can now try debugging again, and should see the break-point hit. But what good is that? To see the cycle count, open the "Processor Status" window:[[File:sim12_pstatus.png]] # This window has a field called ''Cycle Counter'', which is the current clock cycle count. When a breakpoint is hit you can read this field: [[File:sim13_cyclecount.png]] # You can also clear it, writing it to 0 for example at the start of the encryption operation: [[File:sim14_resettozero.png]] # Back to simulating. If you try setting a break-point, you might get an '''open circle''' as below. Note this appeared to be set OK, until we hit ''Debug'' at which point it turned into the open circle! '''<u>This breakpoint will NEVER be hit.</u>'''[[File:sim15_bpnothit.png]] # Instead, you should set a break-point at the higher level code. You can use ''Step Over'' and ''Step into'' to work your way through the code. The following example shows that for the first S-Box substitution, this code is taking almost 1800 cycles. Each run through this loop was taking far too long - the result being that the S-Boxes '''would not''' be covered by the 10 000 samples taken by the CTF system.[[File:sim16_stepin.png]]  == Timing ==