Clash Royale CLAN TAG#URR8PPP

Trying to access first member(itself a volatile pointer) of struct pointer does not return the stored member pointer but the struct address

I am trying to implement some pointer substitution for some communication interface by passing on a pointer to a struct of pointers to some implementation.
This is meant to run on an Atmega328p and is being compiled with avr-gcc.exe (AVR_8_bit_GNU_Toolchain_3.5.4_1709) 4.9.2, installed in/via msys2 64bit on Windows 10

Now, given the following struct

typedef struct
volatile uint8_t* baudrateRegister;
volatile uint8_t* statusRegister;
volatile uint8_t* controlRegister;
volatile uint8_t* dataRegister;
CommRegisters;


I create this as a file scope variable in my main file and fill it with the corresponding addresses (in this case 0xB9, 0xB8, 0xBC, 0xBB) according to my datasheet.

0xB9, 0xB8, 0xBC, 0xBB

CommRegisters myInterface = &BAUDRATEREGISTER, &STATUSREGISTER, &CONTROLREGISTER, &DATAREGISTER;


myInterface itself gets stored in 0x100, for reference sake, consistently.
When i try to access any of them from inside the main function it returns the corresponding and expected addresses.

I then pass that to my init function in a different .c file

CommRegisters* storedRegisters
void init(CommRegisters* registers, uint32_t clockspeed)
storedRegisters = registers;



and when i try to access any of the members i.e. by printing it with printf still in that same init function with

printf("storedRegisters %pn", storedRegisters);
printf("storedRegisters->baudrateRegister %pn", storedRegisters->baudrateRegister);
printf("storedRegisters->statusRegister %pn", storedRegisters->statusRegister);
printf("storedRegisters->controlRegister %pn", storedRegisters->controlRegister);
printf("storedRegisters->dataRegister %pn", storedRegisters->dataRegister);


I should be getting the following addresses printed 0x100, 0xB9, 0xB8, 0xBC, 0xBB, the first one being the struct itself and then the content of each member, being addresses to my registers. Instead accessing storedRegisters->baudrateRegister does return 0x100, the address to the struct itself, not the content of the member.
The output on my console is then

0x100, 0xB9, 0xB8, 0xBC, 0xBB

storedRegisters->baudrateRegister

0x100

storedRegisters 0x100
storedRegisters->baudrateRegister 0x100
storedRegisters->statusRegister 0xb8
storedRegisters->controlRegister 0xbc
storedRegisters->dataRegister 0xbb


With this I cannot access the first member pointer of my struct pointer, but all others seem fine. If I were to swap the order of e.g. control and baudrate register in my struct then the controlregister is the one that returns 0x100.
Am I missing something essential?

I am compiling this with the following options:

avr-gcc -O2 -g2 -gstabs -std=c99 -Wall -funsigned-char -funsigned-bitfields -fpack-struct -fshort-enums -MMD -MP -ffunction-sections -fdata-sections <some files>


and link it with

avr-gcc -Wl,-Map,.map -Wl,-u,vfprintf -lprintf_flt -lm -mmcu=atmega328p <some files>


Edit: Typo fixed

Edit2: i call the init function with

init(&myInterface, 100000L);


Edit3: fixed mixed around console output

Edit4: Added the 3 relevant source files.

The main.c file

#include "CommInterface.h"
#include <avr/io.h>
#include <util/delay.h>

//uart
#include "Debug_uart.h"
static FILE uart_str = FDEV_SETUP_STREAM(uart_putchar, uart_getchar, _FDEV_SETUP_RW);
void startUart(void)
stdout = stdin = &uart_str;
uart_init();
printf("nnnn############################################n");


#define BAUDRATEREGISTER TWBR
#define STATUSREGISTER TWSR
#define CONTROLREGISTER TWCR
#define DATAREGISTER TWDR
CommRegisters myInterface = &BAUDRATEREGISTER, &STATUSREGISTER, &CONTROLREGISTER, &DATAREGISTER;

void integration_runBMETester(void)
startUart();
init(&myInterface, 100000L);
DDRB = (1 << PB5);
while(1)= (1 << PB5);
_delay_ms(500);
PORTB &= ~(1 << PB5);
_delay_ms(500)



int main(int argc, char const *argv)
#ifdef INTEGRATION_BME680
integration_runBMETester();
#endif



The CommInterface.h file

#ifndef _COMM_INTERFACE_H
#define _COMM_INTERFACE_H

#include <stdint.h>

typedef struct
volatile uint8_t* baudrateRegister;
volatile uint8_t* statusRegister;
volatile uint8_t* controlRegister;
volatile uint8_t* dataRegister;
CommRegisters;

void init(CommRegisters* registers, uint32_t clockspeed);

#endif // _COMM_INTERFACE_H


The CommInterface.c file

#include "CommInterface.h"
#include "registerAbstraction.h"

CommRegisters* storedRegisters;
void init(CommRegisters* registers, uint32_t clockspeed)
printf("initn");
storedRegisters = registers;

printf("storedRegisters %pn", storedRegisters);
printf("storedRegisters->baudrateRegister %pn", storedRegisters->baudrateRegister);
printf("storedRegisters->statusRegister %pn", storedRegisters->statusRegister);
printf("storedRegisters->controlRegister %pn", storedRegisters->controlRegister);
printf("storedRegisters->dataRegister %pn", storedRegisters->dataRegister);

abstraction_setRegisterToValue(storedRegisters->statusRegister, 0);
abstraction_setRegisterToValue(storedRegisters->baudrateRegister, ((F_CPU / clockspeed) - 16) / 2);



1 Answer
1

Please excuse this, reputation too low to comment, so I'll just put my 2 cents here.
If it's useless, feel free to downvote and so on.

I compiled and ran the code (adapted for the PC), and assuming the definitions of TWBR and the other 3 to be something like (*(uint8_t *)(0xB9)) , the correct and expected values were printed when the init() function was called in main.
It's hard to figure out without a debugger what's going on at your side, and as I can not see any obvious C errors, at best I can make wild guesses.

TWBR

(*(uint8_t *)(0xB9))

init()

if I were to make an assumption, based on what you said (" If I were to swap the order of e.g. control and baudrate register in my struct then the controlregister is the one that returns 0x100. Am I missing something essential?") I would attempt try to put the blame somewhere in the printf() statements in init().
Would you please try to swap the order of just the printf() calls (e.g. print the data register member first)? And see if the first 2 calls print 0x100 again.

printf()

init()

0x100

printf("storedRegisters %pn", storedRegisters);
printf("storedRegisters->dataRegister %pn", storedRegisters->dataRegister);
printf("storedRegisters->baudrateRegister %pn", storedRegisters->baudrateRegister);
printf("storedRegisters->statusRegister %pn", storedRegisters->statusRegister);
printf("storedRegisters->controlRegister %pn", storedRegisters->controlRegister);


I know it's rudimentary and a bit of caveman debugging, but:
1. I do not have your system to look closer myself
2. You do not have a debugger
3. I see no obvious C errors in the code you posted

registers

init()

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