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This is a thread-aware gdb stub for the lm32 architecture. It has to be
linked with the application, which should be debugged. The application has
to call 'lm32_gdb_stub_install' to setup the stub.
The stub remaps _all_ h/w exceptions to an own code (lm32-debug.S), which
saves all the registers, calls the gdb stub and restores the registers again.
The interrupt exceptions gets handled in a special way. Because we remapped
this exception, we need to do
- the same as the original one (in cpu_asm.S),
- and, as we might use an ISR for breaking into a running application with
gdb, we need to save all registers as well. To be backward compatible
the missing callee saved registers gets appended to CPU_Interrupt_frame.
There is a mapping in 'gdb_handle_break' for that.
To use this gdb stub, your bsp has to provide the following functions:
- void gdb_put_debug_char(char c)
Puts the given charater c to the debug console output. The function can
block until the character can be written to the output buffer.
- char gdb_get_debug_char(void)
Returns the character in the input buffer of the debug console. If no one
is availabe, the function must block.
- void gdb_console_init()
This function can be used to initialize the debug console. Additionally,
it should set up the ISR for the debug console to call the function
'gdb_handle_break', which is provided by the gdb stub and enable the
interrupt for a break symbol on the debug serial port. If no ISR is
provided, you won't be able to interrupt a running application.
- void gdb_ack_irq()
If an ISR is used, this function is used to acknowledge the interrupt.
NOTE: the stub don't skip a hardcoded 'break' in the code. So you have to
set the PC an instruction further in the debugger (set $pc += 4).
NOTE2: make sure you have the following CFLAGS set:
-mbarrel-shift-enabled -mmultiply-enabled -mdivide-enabled
-msign-extend-enabled
Without the hardware support, it is done in software. Unfortunately, the
stub also uses some shifts and multiplies. If you step through your code,
there will be a chance that a breakpoint is set to one of that functions,
which then causes an endless loop.
EXAMPLES
char gdb_get_debug_char(void)
{
/* Wait until there is a byte in RXTX */
while (!(uartread(LM32_UART_LSR) & LM32_UART_LSR_DR));
return (char) uartread(LM32_UART_RBR);
}
void gdb_put_debug_char(char c)
{
/* Wait until RXTX is empty. */
while (!(uartread(LM32_UART_LSR) & LM32_UART_LSR_THRE));
uartwrite(LM32_UART_RBR, c);
}
extern void gdb_handle_break(
rtems_vector_number vector,
CPU_Interrupt_frame *frame
);
void gdb_console_init()
{
rtems_isr_entry old;
/* enable interrupts */
uartwrite(LM32_UART_IER, 1);
rtems_interrupt_catch((rtems_isr_entry) gdb_handle_break, DEBUG_UART_IRQ,
&old);
lm32_interrupt_unmask(1 << DEBUG_UART_IRQ);
}
void gdb_ack_irq()
{
lm32_interrupt_ack(1 << DEBUG_UART_IRQ);
}
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