1.2 Change the OS code to use UART device instead of Mini UART. Use BCM2837 ARM Peripherals and ARM PrimeCell UART (PL011) manuals to figure out how to access UART registers and how to configure GPIO pins. The UART device uses the 48MHz clock as a base.
Summary of registers https://developer.arm.com/documentation/ddi0183/g/programmers-model/summary-of-registers?lang=en
The UART_CR Register is the control register. NOTE: To enable transmission, the TXE bit and UARTEN bit must be set to 1. Similarly, to enable reception, the RXE bit and UARTEN bit, must be set to 1.
NOTE: Program the control registers as follows:
- Disable the UART.
- Wait for the end of transmission or reception of the current character.
- Flush the transmit FIFO by setting the FEN bit to 0 in the Line Control Register, UART_LCRH.
- Reprogram the Control Register, UART_CR. 5. Enable the UART.
Example 3.1 is an example of how to calculate the divisor value.
If the required baud rate is 230400 and UARTCLK = 4MHz then:
Baud Rate Divisor = (4 × 10^6) / (16 × 230400) = 1.085
This means BRDI = 1 and BRDF = 0.085.
Therefore, fractional part, m = integer ( (0.085 × 64) + 0.5 ) = 5
Generated baud rate divider = 1 + 5/64 = 1.078
Generated baud rate = (4 × 10^6) / (16 × 1.078) = 231911