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# Using the debugger
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You are launched into the debugger either by an `ebreak/sbreak` instruction, or when an exception occurs while running executing instructions.
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Consider the example programm `examples/fibs.asm`:
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```asm riscv-asm
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.data
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fibs: .space 56
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.text
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main:
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addi s1, zero, 0 ; storage index
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addi s2, zero, 56 ; last storage index
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addi t0, zero, 1 ; t0 = F_{i}
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addi t1, zero, 1 ; t1 = F_{i+1}
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loop:
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sw t0, fibs(s1) ; save
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add t2, t1, t0 ; t2 = F_{i+2}
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addi t0, t1, 0 ; t0 = t1
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addi t1, t2, 0 ; t1 = t2
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addi s1, s1, 4 ; increment storage pointer
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blt s1, s2, loop ; loop as long as we did not reach array length
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; exit gracefully
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ebreak ; launch debugger
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addi a0, zero, 0
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addi a7, zero, 93
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scall ; exit with code 0
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```
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This calculates the fibonacci sequence and stores it in memory at `fibs`. After it calculated all fibonacci numbers, it
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uses the `ebreak` instruction to open the debugger. Let's run it and see what happens:
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```
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> python -m riscemu examples/fibs.asm
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Successfully loaded: LoadedExecutable[examples/fibs.asm](base=0x00000100, size=72bytes, sections=data text, run_ptr=0x00000138)
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Debug instruction encountered at 0x00000143
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>>>
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```
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In this interactive session, you have access to the cpu, registers, memory and syscall interface. You can look into everything,
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and most common tasks should have helper methods for them.
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Available objects are:
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* `mem`: (aka `mmu` or `memory`)
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* `dump(address, fmt='hex', max_rows=10, group=4, bytes_per_row=16, all=False`:
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Dumps the memory at `address`, in at most `max_rows` rows, each containing `bytes_per_row` bytes grouped
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into groups of `group` bytes. They can be printed as:
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* `hex`: hexadecimal, unsigned
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* `int`: converted to integers
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* `uint`: converted to unsigned integers
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* `symbol(name)`: Lookup all symbols named `name`
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* `reg`: (aka `regs` or `registers`)
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* `dump(full=False)` dumps all integer registers (unless `all` is true, then all registers are printed)
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* `get(name)` get register content
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* `set(name, val)` set register content
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* `cpu`:
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* The CPU has the `pc` attribute and `cycle` attribute. Others won't be useful in this context.
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Example:
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