International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395-0056
Volume: 11 Issue: 01 | Jan 2024
p-ISSN: 2395-0072
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Firmware implementation of UART using Bare metal programming Pavithra K1, Manjunath HV2 1
Student, M.Tech, Electronics and Communication Engineering, Dayananda Sagar College of Engineering Professor, Department of Electronics and Communication Engineering, Dayananda Sagar College of Engineering --------------------------------------------------------------------------***--------------------------------------------------------------------------2
Abstract - The development of real time applications
requires various peripheral interfaces and communication channels. UART is standardized protocol used to establish communication with different hardware. The paper proposes to implement UART protocol at firmware level using bare metal programming model on STM32 CortexM4 microcontroller. The communication is established between two ports of board to demonstrate the implementation and the status and message is displayed on LCD for UI. The implementation provides in depth analysis and reliability of data transfer. Key Words: UART, STM32, Cortex M4, bare metal programming, firmware
1. INTRODUCTION STM32Fxx series of microcontroller supports 2 USART ports that is configured to operate in asynchronous mode. The pins allocated are multiplexed, hence the configuration registers are used to indicate the required operation. Liquid Cristal Display (LCD) is specifically interfaced to indicate different operations being performed during communication. The success and failure of the communication can also be indicated on the panel in real time. Cube IDE (Integrated Development Environment) is configured for STM32F4xx Cortex M4 microcontroller to facilitate programming. Bare metal programming method is used to improve the code efficiency and reduces executable file size. The UART communication is programmed to work in loopback mode and display the status of communication on LCD interfaced. The coding is done in C language to make the code microcontroller architecture independent. (As UART is hardware for asynchronous serial communication, with configurable data format and transmission speeds, data bits are sent one by one from LSB to MSB. For precise timing by communication channel start and stop bits are framed. By cross connection of Tx and Rx pins of two devices using RS232 protocol, bidirectional communication is established.)
and stop bits so that precise timing is handled by the communication channel. The bidirectional communication is established by cross connection of Tx and Rx pins of two devices using RS232 protocol. The pins are multiplexed with more than one operation, by default all port act as input output pins. Therefore, when the transmitter is disabled, the output pin returns to its I/O port configuration. When the transmitter is enabled and nothing is to be transmitted, the Tx pin is at high level. When a transmission is taking place, a write instruction stores the data in the data register and which is copied in the shift register at the end of the current transmission [1]. When no transmission is taking place, a write instruction places the data directly in the shift register, the data transmission starts, and the transmission bit is immediately set. After writing the last data into the data register, it is mandatory to wait for transmission completion bit to set before disabling the UART or causing the microcontroller to enter the low-power mode. During an UART reception, data shifts in least significant bit first through the Rx pin. In this mode, the data register consists of a buffer between the internal bus and the received shift register. When a character is received, the receive completion bit is set which indicates that the content of the shift register is transferred to the receiver data register. The data transmitted should be sampled at the appropriate moment, otherwise there may be a data loss or data may get erroneous. The transmitter and receiver must be compatible on the baud rate to receive data accurately. The different control registers are configured to set appropriate baud rate and establish successful communication which is also verified and validated using status bits. The data word length is 8 bits with NRZ standard format and also includes a parity bit for validation [2]. Data registers available consists a buffer between the internal bus and the transmit shift register.
A universal asynchronous receiver-transmitter is a computer hardware device for asynchronous serial communication in which the data format and transmission speeds are configurable. It sends data bits one by one, from the least significant to the most significant, framed by start
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