Keil Studio Online Assembly - Output on Ports

Keil Studio
1

Hello, I try my first steps in Assembly on Keil Studio Online I did not manage yet to make any output on a port. The Following program does compile witout mistakes and Keil Studio does write the *bin - File on the Nucelo F103 RB. But there is no putput on Port C. Can hely anyone ?

#include “mbed.h”

int main() {

// loop forever
while(true) {
  asm("mov R1,#100");
  asm("mov R7,#50");
  asm("sub R5, R1, R7");
  asm("LDR R3,=0x40020800");
  asm("strb R5,[R3,0x14]");
}

}

2

the initialization stuff is missing, the clock for the port must turned on first and the port configuration set to output.
You can do ths easily by adding a ‘DigitalOut pin(PC_n);’ where PC_n is your gpio.
I don’t know If the asm code is correct, I would never use it.

3

I tried this with in initialization - but there was no effekt. Where can I see, which adresses are reserved for the ports ? In my small assembly Program I assume, that Port C is 0x40020800. But i don’t know if this is true. Somewhere ther must be an configuration file where this is defined.

4

it is in the CMSIS for the target,
mbed-os/targets/TARGET_STM/TARGET_STM32F1/STM32Cube_FW/CMSIS/stm32f103xb.h

5

Thank you for this Tip. This File is very long… have you a hint, where exactly there i find the definitions ? i need to know with which adress I can use in assembly to have access to port A B or C

6

look for:

#define GPIOC_BASE            (APB2PERIPH_BASE + 0x00001000UL)

the base is defined above.
But this is the address of the gpio structure GPIO_TypeDef with several registers, you cannot simply write to this address. Please check the datasheet and reference manual for this mcu.