S4A debugging with avr-gdb and simavr


While this has been possible for a while in S4A, with long workarounds, it got a lot easier in the 5.0 beta IDE.

Using the "open folder" project structure, save work into a folder and build, the "Terminal" button enables. Press it and you're in a terminal session within the folder, with a command line build ready to go. Run "make simulate-gdb" and you have the program running on simavr, with the debug port open for avr-gdb to attach to. Create a separate Terminal window with the same button for your avr-gdb session and run "avr-gdb main.elf" to pick up the image symbols. In the session choose "target remote :1234" and you're in! My preferred run mode for avr-gdb is "layout asm" or "layout reg" (seen here). Obviously it's not for a beginner, but for an experienced gdb jockey it should prove interesting.


Hints

You can find these on other blogs about gdb and simavr. But might be useful here.

To dump memory...
***

(https://sourceware.org/gdb/onlinedocs/gdb/Memory.html)

x/30xb 0x200

...will show 3 bytes in hexadecimal starting at 0x200 but there's a gotcha... gdb usually only expects one memory space, in this case you'll see the contents of "flash" memory (or its simulated equivalent). Simavr has a workaround. RAM (which is what you will usually want to inspect) "starts" at 0x800000!

For example...

(gdb) x/30xb 0x800000

0x800000:       0xd2    0x00    0x00    0x00    0x00    0x00    0x00    0x00
0x800008:       0x00    0x00    0x00    0x00    0x22    0x00    0x22    0x00
0x800010:       0x00    0x00    0x22    0x00    0x1a    0x02    0x18    0x02
0x800018:       0x18    0x02    0x00    0x00    0x47    0x00
...dumping registers shows that is correct...
info reg
r0             0xd2                210
r1             0x0                 0
r2             0x0                 0
r3             0x0                 0
r4             0x0                 0
r5             0x0                 0
r6             0x0                 0
r7             0x0                 0
r8             0x0                 0
r9             0x0                 0
r10            0x0                 0
r11            0x0                 0
r12            0x22                34
r13            0x0                 0
r14            0x22                34
r15            0x0                 0
r16            0x0                 0
r17            0x0                 0
r18            0x22                34
r19            0x0                 0
r20            0x1a                26
r21            0x2                 2
r22            0x18                24
r23            0x2                 2
r24            0x18                24
r25            0x2                 2
r26            0x0                 0
r27            0x0                 0
r28            0x47                71
r29            0x0                 0
r30            0x18                24
r31            0x2                 2
SREG           0x80                128
SP             0x8f7               0x8008f7
PC2            0x148               328
pc             0xa4                0x148 <main+98>

(remember the first 32 bytes of RAM on AVR map to the 32 registers r0-r31)

To control TUI...
***
You can find this easily in Google but posted here to save a search: (https://sourceware.org/gdb/onlinedocs/gdb/TUI-Keys.html)
Handy keys:
C-x a  ... leave TUI
C-x o  ... move to next window (so you can scroll code or commands)
C-L ... reload the screen if it gets garbled

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