Downloading dependecies

• STM32 Programming Toolset + dependencies

  sudo apt-get install git make cmake libusb-1.0-0-dev
  sudo apt-get install gcc build-essential
  
  wget https://github.com/stlink-org/stlink/releases/download/v1.8.0/stlink_1.8.0-1_amd64.deb -q --show-progress
  sudo dpkg -i stlink_1.8.0-1_amd64.deb

  Connect the board to an USB port and to test its connectivity you can execute the followind command:

  lsusb | grep STM 
  Expected output: STMicroelectronics ST-LINK/V2.1

  The COM LED should also be green. A problem with USB enumeration is indicated by a blinking red COM LED.

  To see more specific information about the board you can execute the following command:

  st-info --probe
  
  Found 1 stlink programmers
      version:    V2J37S27
      serial:     066BFF373146363143223537
      flash:      524288 (pagesize: 2048) (512KB)
      sram:       147456 (144KB)
      chipid:     0x467
      dev-type:   STM32G0Bx_G0Cx
  

Startup Script

ARM Cortex-M0+ Reset Behavior

The Cortex-M0+ has the following reset behavior according to this well documented presentation here:

• Reads the Initial SP, also called the MSP (Main Stack Pointer)
• Reads the reset vector
• Branches to the starting of the program execution address (reset handler)
• Subsequently executes program instructions (TBD in the Reset_Handler function)

Reset_Handler

A strong reference point was this forum post and also this implementation for the STM32H7xx series.

1. Define the interrupt vector table for the NVIC according to the Cortex-M0+ Manual and STM32G0x1xx series reference Manual.

void (* g_pfnVectors[])(void) __attribute__((section (".isr_vector"))) = {...}

2. Move the MSP to the SP (Stack Pointer) using inline assembly and LDR instruction (see page 141 from ARMv6-m Architecture Manual). It uses the _estack symbol defined in the linker script.

__asm (
      "LDR R0, =_estack       \n\t"
      "MOV SP, R0             \n\t"
  );

3. Initialize the .data section. In order to use symbols from the .data section, the startup code needs to copy the data from LMA (Flash) to VMA (SRAM) to make sure that all C code can access the initialized data. It uses the _data_start, data_end symbols for the virtual adresses and _sidata symbol for the start address of the LMA of the .data section.

uint32_t *dataSrc = &_sidata, *dataDest = &_data_start;
  while (dataDest < &_data_end) {
      *dataDest++ = *dataSrc++;
  }

4. Initialize the .bss section to zero using inline assembly. It uses the _bss_start and _bss_end symbols defined in the linker script.

  __asm (
      "LDR R0, =_bss_start      \n\t"
      "LDR R1, =_bss_end        \n\t"
      "MOV R2, #0               \n\t"
      "loop_zero:               \n\t"
      "   CMP 	R0, R1          \n\t"
      "   BGE 	end_loop        \n\t"
      "   STR	R2, [R0]        \n\t"
      "   ADD   R0, R0, #4      \n\t"
      "   B 	loop_zero       \n\t"
      "end_loop:                \n\t"
  );

System_Init

The purpose of this function is to configure the PLL Block of the Clock tree with a frequency of 64 MHz and to select PLLRCLK as the SYSCLK source.

The formula by which the output f_PLLR is calculated is the following:

fPLLR = ((fPLLIN / M) * N) / R,
where:
  - fPLLIN is the frequency of HSI16 clock source of 16 MHz
  - M, N and R are configurable parameters using PLLCFGR register

Documentation

• STM32G0x1xx Reference Manual
  • Memory Organization (Chapter 2.2.2 Memory map and register boundary addresses - pg. 62)
  • System Clock Selection (Chapter 5. Reset and clock control (RCC) - pg. 155)
• STM32 Cortex-M0/M0+ Programming Manual
• ARMv6-M Architecture Reference Manual

Linker Script

KEYWORD	DESCRIPTION
SECTIONS	Defines the mapping between the sections of the input object files to the sections of the linker's output file, by specifying the memory layout of each output section.
KEEP	Tells the linker to not remove the section wrapped by this command. Important when working with ARM microprocessors because the interrupt vector table must be in a predefined memory location and is not referenced directly by code.
LMA	Load Memory Address.
VMA	Virtual Memory Address.
.	Location Counter.
ALIGN	Introduces the required amount of padding to align the location counter.

Usage

To be able to run the rules inside the provided Makefile you are required to also install the ARM GNU Toolchain:

  sudo apt-get install gcc-arm-none-eabi

1. Create .hex file using the Makefile rule:

make all

2. Flash the device

st-flash --format ihex write program.hex

2024-12-22T16:36:26 INFO common.c: STM32G0Bx_G0Cx: 144 KiB SRAM, 512 KiB flash in at least 2 KiB pages.
2024-12-22T16:36:26 WARN common_flash.c: Flash base use default L0 address
2024-12-22T16:36:26 INFO common_flash.c: Attempting to write 508 (0x1fc) bytes to stm32 address: 134217728 (0x8000000)
-> Flash page at 0x8000000 erased (size: 0x800)
2024-12-22T16:36:26 INFO flash_loader.c: Starting Flash write for WB/G0/G4/L5/U5/H5/C0

2024-12-22T16:36:26 INFO common_flash.c: Starting verification of write complete
2024-12-22T16:36:26 INFO common_flash.c: Flash written and verified! jolly good!
2024-12-22T16:36:26 INFO common.c: Go to Thumb mode

(OPTIONAL) 3. Start a gdb connection using st-util and connect locally using gdb-multiarch

sudo apt-get install gdb-multiarch

# Inside the first terminal window
st-util

# Inside the second terminal window
gdb-multiarch

(gdb) file program.hex
(gdb) target remote localhost:4242
(gdb) ...