An example program to be debugged has the keyboard
monitor included at the end. This program can be downloaded and assembled without
modification to test the monitor. The example program under test transmits a
number and a constant string to the PC terminal emulator as long as
and stops if
RXchar<>'g'. Note that this use of a
command is not the monitor command, but the program under test. The monitor
does nothing until the user presses '
esc' on the PC keyboard, then
'>' prompt. At this point any of the other monitor
commands may be used. Near the beginning of the program there is a short macro
defined which calls the UART RXdone ISR as a subroutine. This produces a software
interrupt to enter the monitor. The macro is shown below.
.macro break cli rcall RXisr .endmacro
Whenever the symbol
break is inserted into the program under test,
the monitor will be entered without a keystroke from the user. All of the monitor
commands can them be used.
Note that the example program defines a interrupt vector to
and defines a register called
RXchar to receive characters. Due
to the way registers are saved in the ISR,
RXchar must be a register
r27. The program under test might start with:
;a received character passed back from RXisr .def RXchar =r20 ;RXchar must be in a register below r27 ;The following macro calls the ISR as if it is a subroutine ;You can put it your program whenever you want to enter the ;keyboard monitor .macro break cli rcall Monitor .endmacro .cseg .org $0000 rjmp RESET ;reset entry vector reti reti reti reti reti reti reti reti rjmp RXisr ;UART receive and monitor entry reti reti reti RESET: ldi temp, LOW(RAMEND) ;setup stack pointer out SPL, temp ldi temp, HIGH(RAMEND) out SPH, temp ;setup UART -- enable RXdone int, and RX, TX pins ldi temp, 0b10011000 out UCR, temp ;set baud rate to 9600 ldi temp, 25 ;9600 baud out UBRR, temp ;the rest of the program under test ... ... ;at the end iclude the monitor .include "keymon1.inc"
An include file with just the keyboard monitor can be inserted at the end of any program unter test.