Arduino Leonardo汇编骰子程序故障：跳过roll_dice循环显示值为0

Hey folks, I'm troubleshooting an Arduino Leonardo assembly program for a dice rolling feature that's misbehaving badly. Here's what it should do:

• Display "Welcome"
• Wait 1 second
• Show the prompt: "Press 2 to(Str_roll_1) roll(Str_roll_2)"
• When the 2 key is pressed, keep rolling the dice until the key is released
• Display and store the final dice value
• Loop back to the initial prompt

Instead, it skips the actual dice rolling logic entirely and gets stuck in an infinite loop showing "Rolling..." → "Value: 0" → "Rolling..." → "Value: 0" nonstop.

Core Code Snippets #

Main Program

main:
PRINTSTRING Str_welcome
RCALL delay_1_s
RCALL lcd_clear_display
PRINTSTRING Str_roll_1
LDI RVAL, 0xC0
RCALL lcd_write_instr
PRINTSTRING Str_roll_2
loop:
CALL read_keyboard
LDI R25, 0x04
CP R25, RVAL
BREQ two
RJMP loop
two:
RCALL lcd_clear_display
PRINTSTRING Str_rolling
RCALL delay_1_s
RCALL roll_dice
RCALL store_stat
RCALL lcd_clear_display
PRINTSTRING Str_value
SUBI R24, -48
RCALL lcd_write_chr
RCALL delay_1_s
RJMP cont
cont:
RCALL lcd_clear_display
PRINTSTRING Str_roll_1
LDI RVAL, 0xC0
RCALL lcd_write_instr
PRINTSTRING Str_roll_2
RJMP loop

roll_dice Subroutine

roll_dice:
LDI R16, 6
test:
NOP
NOP
RCALL read_keyboard
CPI RVAL, 0x04
BREQ roll
RET
roll:
DEC R16
BREQ roll_dice
RJMP test

Keyboard Handling Code

map_table: .DB "147*2580369#"
read_keyboard:
LDI R18, 0 ; reset counter
LDI ZH, high(map_table <<1) ;Initialize Z pointer
LDI ZL, low(map_table <<1)
ADD ZL, RVAL ;Add index
LDI RVAL, 0x00
ADC ZH, RVAL ;Add 0 to catch Carry, if present
LPM RVAL, Z
scan_key:
MOV R19, R18
LSL R19
LSL R19
LSL R19
LSL R19
OUT PORTB, R19 ; set column and row
insert 22 NOP lines here
SBIC PINE, 6
RJMP return_key_val
INC R18
CPI R18, 12
BRNE scan_key
LDI R18, NO_KEY ; no key was pressed!
return_key_val:
MOV RVAL, R18
RET

Troubleshooting Breakdown & Fixes #

Let's walk through the critical issues causing the failure:

1. Broken read_keyboard Logic

   • The routine starts by trying to index into map_table using RVAL—but RVAL hasn't been initialized yet! This means you're using garbage data to look up a key, leading to unpredictable return values.
   • The actual keyboard scan (scan_key) happens after this broken lookup, so the key state you're checking in the main loop and roll_dice is unreliable.
   • Fix: Move the map_table lookup to after the keyboard scan. Since your main code checks for the key index (0x04 for the '2' key), you could even skip the map lookup entirely here and just return R18 directly.

2. Backwards Logic in roll_dice

   • Right now, roll_dice returns immediately if the 2 key is not pressed, and loops if it is pressed—this is the opposite of your intended behavior (you want to roll while the key is held, then return when released).
   • Additionally, when R16 hits 0, you jump back to roll_dice to reinitialize it, creating an infinite loop if the key stays held.
   • Fix: Rewrite the subroutine to loop while the key is pressed, generate a random dice value each iteration, and return only when the key is released.

3. No Dice Value Generation

   • Nowhere in your code do you actually generate a random number between 1-6 and store it in R24 (which the main routine tries to print). That's why you're seeing "Value: 0"—R24 is never set to a valid dice value.
   • Fix: Add logic to generate a random value (use an uninitialized register or timer tick as a seed, since AVRs lack hardware randomness) and store it in R24 before returning from roll_dice.

4. Main Loop Key Check Reliability

   • The main loop checks if RVAL equals 0x04 (the index of '2' in map_table), which is correct—but only if read_keyboard is returning accurate index values. Fixing the keyboard routine will resolve this.

内容的提问来源于stack exchange，提问作者Isac Oskarsson