{"id":74,"date":"2025-03-26T08:44:45","date_gmt":"2025-03-26T08:44:45","guid":{"rendered":"https:\/\/tech-kid.de\/wp\/?page_id=74"},"modified":"2025-03-26T18:36:36","modified_gmt":"2025-03-26T18:36:36","slug":"stm8-how-i-do-it","status":"publish","type":"page","link":"https:\/\/tech-kid.de\/wp\/?page_id=74","title":{"rendered":"STM8 – How I do it"},"content":{"rendered":"\n

Since I’m coming a little more from the hardware-side of those projects, I prefer data sheets and low-level documentation. When tinkering with microcontrollers, I often had the feeling, that I spent too much time “reverse-engineering” overpowered abstraction layers, bringing together the code and what was really going on on the machine. I then decided to code the stuff as they call it “bare-metal”. The disadvantage is clear: the code may not be as re-usable as it could be. On the other side, I like to use the low-level user manuals directly for programming, because this kind of documentation is very reliable and comprehensive. Additionally, if coding some “non-standard” usage of peripherals, one would fall back to “register level” easily; so why not only code like this when tinkering near to the hardware? <\/p>\n\n\n\n

On the coding level, when I want to use some peripheral, I define a pointer variable that points to a stuct. The struct represents the registers which are described in the Reference Manual of the \u00b5C. The addresses of the peripherals are defines in the header file. This way, I can just copy the information from the Reference Manual and the documentation of the manufacturer can directly be found in my code.<\/p>\n\n\n\n

The following is an example of “bare-metal” definitions for the UART-Peripheral of my STM8L in a header file (stm8l15x_usart.h<\/strong>):<\/p>\n\n\n\n

#ifndef __STM8L15x_USART_H\n#define __STM8L15x_USART_H\n\n#include \"STM8L15x.h\"\n\n#define USART1_OFFS (USART_t*)0x005230\n#define USART2_OFFS (USART_t*)0x0053E0\n#define USART3_OFFS (USART_t*)0x0053F0\n\n#define QQ_BAUD_16M_115k2 \t(uint16_t)0x008B\n#define QQ_BAUD_16M_9k6\t\t(uint16_t)0x0683\n\nstruct USART_s\n{\n    volatile uint8_t SR;\n    volatile uint8_t DR;\n    volatile uint8_t BRR1;\n    volatile uint8_t BRR2;\n    volatile uint8_t CR1;\n    volatile uint8_t CR2;\n    volatile uint8_t CR3;\n    volatile uint8_t CR4;\n    volatile uint8_t CR5;\n    volatile uint8_t GTR;\n    volatile uint8_t PSCR;\n};\ntypedef volatile struct USART_s USART_t;\n\nvoid usart_init(uint32_t baudrate);\n\n#endif\/\/__STM8L15x_USART_<\/code><\/pre>\n\n\n\n
The corresponding register set is defined in the STM8L Reference Manual:<\/p>\n\n\n\n


\"\"
USART Peripheral Register Set of STM8L MCUs (Excerpt from Reference Manual<\/a>)<\/figcaption><\/figure>

<\/div>\n\n\n\n
Depending on the need of initialization functions for the peripheral, I create a c-file (e.g. stm8l15x_usart.c<\/strong>) and link the resulting object file into the project, or not.<\/p>\n\n\n\n
#include \"STM8L15x_USART.h\"\n\nextern USART_t *USART;\nextern GPIO_t *PORTG;\nextern CLK_t *CLK;\n\n\nvoid usart_init(uint32_t baudrate) \n{\n    uint16_t baud_div;\n\t\n    CLK->PCKENR3 |= (1<<4\/*USART3 Enable*\/);\n\n    if(baudrate == 9600)\n    {\n    \tbaud_div = QQ_BAUD_16M_9k6;\n    }\n    else\n    {\n    \tbaud_div = QQ_BAUD_16M_115k2;\n    }\n \n    \/\/ Set Baud Rate\n    USART->BRR2 =  (baud_div & 0x0F) | ((baud_div >> 8) & 0xF0); \n    \/\/ LSB\n    USART->BRR1 =  (baud_div >> 4) & 0xFF; \/\/ MSB\n   \n\n    \/\/ Init Control Regs\n    USART->CR1 = 0x00; \/\/ 8N1\n    USART->CR2 = 0x0C; \/\/ RX ON, TX ON \n    \n    \n    PORTG->DDR |= 2;\n    PORTG->CR1 |= 2;\n}<\/code><\/pre>\n\n\n\n
<\/p>\n","protected":false},"excerpt":{"rendered":"
Since I’m coming a little more from the hardware-side of those projects, I prefer data sheets and low-level documentation. When tinkering with microcontrollers, I often had the feeling, that I spent too much time “reverse-engineering” overpowered abstraction layers, bringing together the code and what was really going on on the machine. I then decided to … <\/p>\n
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