[Education] Demystifying Microcontrollers: Using ATmega328P and Assembly to Understand Registers

Projects General Guidance
1556

Here is my Nano clone made in China (my own sketch):

Test - print memory I/O registers

0x0020 value = 0x02
0x0021 value = 0x04
0x0022 value = 0x04
0x0023 value = 0x00
0x0024 value = 0x00
0x0025 value = 0x00
0x0026 value = 0x00
0x0027 value = 0x00
0x0028 value = 0x00
0x0029 value = 0x03
0x002A value = 0x00
0x002B value = 0x00
0x002C value = 0x04
0x002D value = 0x04
0x002E value = 0x04
0x002F value = 0x04
0x0030 value = 0x04
0x0031 value = 0x04
0x0032 value = 0x04
0x0033 value = 0x04
0x0034 value = 0x04
0x0035 value = 0x04
0x0036 value = 0x00
0x0037 value = 0x00
0x0038 value = 0x04
0x0039 value = 0x04
0x003A value = 0x04
0x003B value = 0x00
0x003C value = 0x00
0x003D value = 0x00
0x003E value = 0x00
0x003F value = 0x00
0x0040 value = 0x00
0x0041 value = 0xFF
0x0042 value = 0x03
0x0043 value = 0x00
0x0044 value = 0x02
0x0045 value = 0x04
0x0046 value = 0x33
0x0047 value = 0x3F
0x0048 value = 0x00
0x0049 value = 0x04
0x004A value = 0x00
0x004B value = 0x00
0x004C value = 0x00
0x004D value = 0x00
0x004E value = 0x00
0x004F value = 0x04
0x0050 value = 0x30
0x0051 value = 0xFF
0x0052 value = 0x04
0x0053 value = 0x00
0x0054 value = 0x00
0x0055 value = 0x00
0x0056 value = 0x04
0x0057 value = 0x00
0x0058 value = 0x04
0x0059 value = 0x04
0x005A value = 0x04
0x005B value = 0x00
0x005C value = 0x04
0x005D value = 0xF7
0x005E value = 0x08
0x005F value = 0xB5
0x0060 value = 0x00
0x0061 value = 0x00
0x0062 value = 0x04
0x0063 value = 0x04
0x0064 value = 0x00
0x0065 value = 0x04
0x0066 value = 0xCA
0x0067 value = 0x04
0x0068 value = 0x00
0x0069 value = 0x00
0x006A value = 0x04
0x006B value = 0x00
0x006C value = 0x00
0x006D value = 0x00
0x006E value = 0x02
0x006F value = 0x00
0x0070 value = 0x00
0x0071 value = 0x04
0x0072 value = 0x04
0x0073 value = 0x04
0x0074 value = 0x04
0x0075 value = 0x04
0x0076 value = 0x04
0x0077 value = 0x04
0x0078 value = 0x00
0x0079 value = 0x00
0x007A value = 0x87
0x007B value = 0x00
0x007C value = 0x00
0x007D value = 0x04
0x007E value = 0x00
0x007F value = 0x00
0x0080 value = 0x00
0x0081 value = 0x00
0x0082 value = 0x00
0x0083 value = 0x04
0x0084 value = 0x00
0x0085 value = 0x00
0x0086 value = 0x00
0x0087 value = 0x00
0x0088 value = 0x00
0x0089 value = 0x00
0x008A value = 0x00
0x008B value = 0x00
0x008C value = 0x04
0x008D value = 0x04
0x008E value = 0x04
0x008F value = 0x04
0x0090 value = 0x04
0x0091 value = 0x04
0x0092 value = 0x04
0x0093 value = 0x04
0x0094 value = 0x04
0x0095 value = 0x04
0x0096 value = 0x04
0x0097 value = 0x04
0x0098 value = 0x04
0x0099 value = 0x04
0x009A value = 0x04
0x009B value = 0x04
0x009C value = 0x04
0x009D value = 0x04
0x009E value = 0x04
0x009F value = 0x04
0x00A0 value = 0x04
0x00A1 value = 0x04
0x00A2 value = 0x04
0x00A3 value = 0x04
0x00A4 value = 0x04
0x00A5 value = 0x04
0x00A6 value = 0x04
0x00A7 value = 0x04
0x00A8 value = 0x04
0x00A9 value = 0x04
0x00AA value = 0x04
0x00AB value = 0x04
0x00AC value = 0x04
0x00AD value = 0x04
0x00AE value = 0x04
0x00AF value = 0x04
0x00B0 value = 0x00
0x00B1 value = 0x00
0x00B2 value = 0x00
0x00B3 value = 0x00
0x00B4 value = 0x00
0x00B5 value = 0x04
0x00B6 value = 0x00
0x00B7 value = 0x04
0x00B8 value = 0x00
0x00B9 value = 0xF8
0x00BA value = 0xFE
0x00BB value = 0xFF
0x00BC value = 0x00
0x00BD value = 0x00
0x00BE value = 0x04
0x00BF value = 0x04
0x00C0 value = 0x62
0x00C1 value = 0x98
0x00C2 value = 0x06
0x00C3 value = 0x04
0x00C4 value = 0x10
0x00C5 value = 0x00
0x00C6 value = 0x00
0x00C7 value = 0x04
0x00C8 value = 0x04
0x00C9 value = 0x04
0x00CA value = 0x04
0x00CB value = 0x04
0x00CC value = 0x04
0x00CD value = 0x04
0x00CE value = 0x04
0x00CF value = 0x04
0x00D0 value = 0x04
0x00D1 value = 0x04
0x00D2 value = 0x04
0x00D3 value = 0x04
0x00D4 value = 0x04
0x00D5 value = 0x04
0x00D6 value = 0x04
0x00D7 value = 0x04
0x00D8 value = 0x04
0x00D9 value = 0x04
0x00DA value = 0x04
0x00DB value = 0x04
0x00DC value = 0x04
0x00DD value = 0x04
0x00DE value = 0x04
0x00DF value = 0x04
0x00E0 value = 0x04
0x00E1 value = 0x04
0x00E2 value = 0x04
0x00E3 value = 0x04
0x00E4 value = 0x04
0x00E5 value = 0x04
0x00E6 value = 0x04
0x00E7 value = 0x04
0x00E8 value = 0x04
0x00E9 value = 0x04
0x00EA value = 0x04
0x00EB value = 0x04
0x00EC value = 0x04
0x00ED value = 0x04
0x00EE value = 0x04
0x00EF value = 0x04
0x00F0 value = 0x04
0x00F1 value = 0x04
0x00F2 value = 0x04
0x00F3 value = 0x04
0x00F4 value = 0x04
0x00F5 value = 0x04
0x00F6 value = 0x04
0x00F7 value = 0x04
0x00F8 value = 0x04
0x00F9 value = 0x04
0x00FA value = 0x04
0x00FB value = 0x04
0x00FC value = 0x04
0x00FD value = 0x04
0x00FE value = 0x04
0x00FF value = 0x04

Seems like except the first unused byte value 0x02, the all other unused are 0x04.
BTW I tried to write 0xAA to the address 0x20 and no change, still 0x02.

1557

AI might suggest (rightly) that "pbi 5,5" was poor style but it wouldn't reject it. It's more likely to suggest that an instructor might explain that the numeric form is more like what the CPU sees but that the symbolic form is normally preferred in finished programs.

Raher than call you a liar I'm going to suggest that you have created this from whole cloth like many of your other arguments.

This suggests that you at least have a sense of humor. AI calls your "tool" a "toy" so at least that shows that it appreciates a good joke as well.

You asked me to query AI and I gave it this prompt:
"Are you familiar with the costycnc AVR1 tool? What is your opinion of it as a teaching aid?"
I copy/pasted its summary remark. It went on at length justifying that opinion and you might use the same prompt to find and correct the issues it found.

1558

not need to be:

uint8_t pinA = PINA;
uint8_t ddrA = DDRA;
uint8_t portA = PORTA;

???

1559

"The AI didn't invent the 'tool' or 'toys' itself. AI found what I wrote on my pages; I have always written that my tool is a 'toy', you can check all my pages!"

1560

Except here where you frequently call it a "tool."

1561

Maybe you could save a lot of work and just post several links.
I'll archive your site's current state for comparison.

1562

I did , many times, i have some practical knowledge about atmega328, some js, some python, some c,some avr asm ,my knowledge is 0,001% from academic knowledge , and i not undertstand because this ostile comportaments vs me , a carpenter , i did that if a carpenter like me undestand some principles , i think that any students without much efort can see atmega 328 underhood , some princoples that perhaps change little mentality and watch with another "eyes" the abstract programming , perhaps help to understand better some underground principles that perhaps is not easy to explain with abstract .I did ,my program is a toy , a principiant or a student can spend 1 minute to open costycnc tool directly from web ,make a sbi 5,5 and ledon , and after can dont touch costycnc for ever, but perhaps some of them can be util costycnc tool. because today a tool assembler, uploader directly from web not exists! I know , perhaps after some weeks, months , or years appear many tools like mine , and for me is a felicity , and more complete that mine , but today not exists a complete tool in one web page compiler and uploader! that is point!

1563

I think that is good advice. Demystification complete.

1564

costycnc avr tool (based on avrlass) accept also macro:

    init
LOOP:
    sbi 3,5
    wait 30
rjmp LOOP

;------------------- MACRO ZONE ------------------------------------

.macro init
    .org 0
    rjmp init
     .org 0x60
    init:
.endmacro

.macro wait
     ldi r18,@0
     wait1:
     inc r16
     brne wait1
     inc r17
     brne wait1
     dec r18
     brne wait1
.endmacro

Compile and upload now https://costycnc.github.io/avr-compiler-js/?code=arduino-forum/macro-blink.asm

1565

Here serial example with macro and interrupt,if send 'A' toggle led D13 ,if not 'A' nothing happen

init
enable_serial_interrupt
loop:
    rjmp loop

serial_interrupt:
    lds r18, 0xC6  ; Read byte from UDR0
    cpi r18, 'A'   ; Is it 'A'?
    brne jos
    sbi 3,5; Toggle PB5 (Built-in LED) on match
jos:
    reti
    
;---------------------------------MACRO ZONE------------------------------------------------------
.macro init
.org 0x0000
    jmp RESET
.org 0x0024        ; USART RX Complete Interrupt vector
    jmp serial_interrupt
.org 0x0060
RESET:
    sbi 0x04, 5    ; DDRB: Set PB5 as output
.endmacro
.macro enable_serial_interrupt 
    ldi r16, 103   ;bauds 9600
    sts 0xC4, r16  ; Write to UBRR0L
    ldi r16, 0b00000110 ; Set UCSZ01 and UCSZ00 bits 8N1
    sts 0xC2, r16      ; Write to UCSR0C
    ldi r16, 0b10010000 ; Set RXCIE0 and RXEN0 bits activate rx_interrupt
    sts 0xC1, r16      ; Write to UCSR0B
    sei                ; Enable global interrupts
.endmacro
    sts 0xC2, r16      ; Write to UCSR0C
    ldi r16, 0b10010000 ; Set RXCIE0 and RXEN0 bits
    sts 0xC1, r16      ; Write to UCSR0B
    sei                ; Enable global interrupts
.endmacro

Try now https://costycnc.github.io/avr-compiler-js/?code=arduino-forum/usart/macro-usart-int.asm

Ai did:

"The AVR assembly code for the ATmega328P (Arduino Uno) has three main issues that prevent it from working correctly: the Stack Pointer is not initialized, the sbi command does not toggle the LED as expected, and the incorrect placement of the macros and interrupt vectors prevents the code from executing initially."

But is important what did AI and stop? or continue to understand the code and understand because AI did that this code not working ,when in realty working?

1566

Is this an example of ASM code that someone who cannot understand what digitalWrite(13, HIGH); does is expected to understand ?

1567

Why not ret in place of reti?

1568

test for you!:grinning_face:

because is return from interrupt

1569

The execution of ret will also bring the MCU back to the interrupted program.

1570

yes ,but flag interrupt rimain active

1571

But does ret re-enable the interrupt flag ?

1572

test was for me!:grinning_face:

1573

Dear @costycnc,

Since you're here on the forum, why not take this opportunity to turn some of your uncertainties into new knowledge? You might just need to loosen your tie to your beloved assembly language a little and explore a few new ideas.

Before the MCU vectors to the ISR, the I-bit is automatically cleared, disabling global interrupts. As a result, no further interrupts are accepted during the execution of the ISR. When the RETI instruction is executed, the I-bit is restored, control returns to the main program (MLP), and the MCU executes at least one machine instruction before responding to the next pending/new interrupt.

The RET instruction, on the other hand, does not restore the I-bit. Consequently, global interrupts remain disabled, and the MCU will not respond to any further interrupts.

1575

dont remember that you make experiment , in this thread or another?

dont remember if 1 is activate or 0 ,but remeber that already speak about this!

1576

"I was pretty close, I deserve at least a passing grade for that!"

yes i remember,you make experiment!