esp32-c3-uart-interface.c

#include "esp32-c3-uart-interface.h"

static void clearBits(volatile uint32_t *registerAddress, uint32_t bitPositions, uint32_t numBits) {
    uint32_t mask = (uint32_t)(1 << numBits) - 1;
    mask <<= bitPositions;
    *registerAddress &= ~mask;
}

static void setBit(volatile uint32_t *registerAddress, uint32_t bitPositions) {
    uint32_t mask = (uint32_t)(1 << bitPositions);
    *registerAddress |= ~mask;
}

static void init_uart_enable_clk(){
  // enable the clock for UART RAM by setting SYSTEM_UART_MEM_CLK_EN to 1;
  // enable APB_CLK for UARTn by setting SYSTEM_UARTn_CLK_EN to 1;
  uint32_t perip_clk_en0 = *C3_SYSTEM_PERIP_CLK_EN0_REG;
  perip_clk_en0 |= 1<<24;
  perip_clk_en0 |= 1<<5;
  perip_clk_en0 |= 1<<2;
  *C3_SYSTEM_PERIP_CLK_EN0_REG = perip_clk_en0;
}

static void init_uart_toggle_rst(){
  // Detailed steps explained in 26.5.2.1
  // for resetting and initilizing of uart
  // get current regestry values
  uint32_t rx_filt = *C3_UART_RX_FILT_REG_UART0;
  uint32_t core_value = *C3_UART_CLK_CONF_REG_UART0;
  // clear UARTn_RST
  rx_filt &= (uint32_t)~(1<<5);
  rx_filt &= (uint32_t)~(1<<2);
  *C3_UART_RX_FILT_REG_UART0 = rx_filt;
  // set UART_RST_CORE
  core_value |= 1<<23;
  *C3_UART_CLK_CONF_REG_UART0 = core_value;
  // set UARTn_RST
  rx_filt |= 1<<5;
  rx_filt |= 1<<2;
  *C3_UART_RX_FILT_REG_UART0 = rx_filt;
  // clear UARTn_RST
  rx_filt &= (uint32_t)~(1<<5);
  rx_filt &= (uint32_t)~(1<<2);
  *C3_UART_RX_FILT_REG_UART0 = rx_filt;
  // clear UART_RST_CORE
  core_value &= (uint32_t)~(1<<23);
  *C3_UART_CLK_CONF_REG_UART0 = core_value;
}

static void init_uart_clear_update(){  
  // enable register synchronization by clearing UART_UPDATE_CTRL.
  uint32_t id_value = *C3_UART_ID_REG_UART0;
  id_value &= (uint32_t)~(1<<30);
  *C3_UART_ID_REG_UART0 = id_value;
}

static void config_clock_freq(){
  //freq = clock source rate / (UART_SCLK_DIV_NUM+UART_SCLK_DIV_A/UART_SCLK_DIV_B)
  // baud rate = freq / (UART_CLKDIV + UART_CLKDIV_FRAG / 16)

  // select the clock source via UART_SCLK_SEL;
  uint32_t clockSelect = *C3_UART_CLK_CONF_REG_UART0;
  // making sure we start with 0
  clockSelect &= (uint32_t)~(1<<20);
  clockSelect &= (uint32_t)~(1<<21);
  // 01 is ABP_CLK with 80 MHz
  // 10 is RC_FAST_CLK with default of 17.5 MHz
  // 11 is XTAL_CLK with 40 MHz
  clockSelect |= 1<<20;
  *C3_UART_CLK_CONF_REG_UART0 = clockSelect;
  // selected ABP_CLK with 80 MHz

  // dividing clock to 6 Mhz (divisor should be 13+1/3)
  // UART_SCLK_DIV_NUM
  clockSelect |= 1<<12;
  clockSelect |= 1<<14;
  clockSelect |= 1<<15;

  // UART_SCLK_DIV_A
  clockSelect |= 1<<6;

  // UART_SCLK_DIV_B
  clockSelect |= 1<<1;
  clockSelect |= 1<<0;

  *C3_UART_CLK_CONF_REG_UART0 = clockSelect;

  // calculate Baud rate to be 9600 (6Mhz/625)
  uint32_t baudRateDivs = *C3_UART_CLKDIV_REG_UART0;
  baudRateDivs |= 1<<0;
  baudRateDivs |= 1<<4;
  baudRateDivs |= 1<<5;
  baudRateDivs |= 1<<6;
  baudRateDivs |= 1<<9;
  *C3_UART_CLKDIV_REG_UART0 = baudRateDivs;
}

static void disable_parity(){
  uint32_t uart_conf = *C3_UART_CONF0_REG_UART0;
  uart_conf &= (uint32_t)~(1<<0);
  uart_conf &= (uint32_t)~(1<<1);
  *C3_UART_CONF0_REG_UART0 = uart_conf;
}

static void set_max_data_lenght(){
  uint32_t uart_conf = *C3_UART_CONF0_REG_UART0;
  uart_conf |= (1<<2);
  uart_conf |= (1<<3);
  *C3_UART_CONF0_REG_UART0 = uart_conf;
}

void config_uart(){
  printf("Try to config %d\n", 1);
  // wait for UART_REG_UART0_UPDATE to become 0, which indicates the completion of the last synchronization;
  uint32_t reg_update = *C3_UART_ID_REG_UART0;
  if ((bool)(reg_update & (uint32_t)(1<<31))){
    return;
  }

  printf("Ready to config %d\n", 1);

  // configure static registers (if any) following Section 26.5.1.2;

  // set clock freq to 6MHz
  // baud rate to 9600
  config_clock_freq();

  // configure data length via UART_BIT_NUM;
  set_max_data_lenght();

  // configure odd or even parity check via UART_PARITY_EN and UART_PARITY;
  disable_parity();
  
  // synchronize the configured values to the Core Clock domain by writing 1 to UART_REG_UPDATE.
  reg_update |= (uint32_t)(1<<31);
  *C3_UART_ID_REG_UART0 = reg_update;
}

static void set_65_to_rd_byte(){
  uint32_t rx_fifo = *C3_UART_FIFO_REG_UART0;
  // making sure we start with 0
  rx_fifo |= 1<<0;
  rx_fifo |= 1<<6;
  *C3_UART_FIFO_REG_UART0 = rx_fifo;

}

void enable_uart_transmitter(){
  // configure TX FIFO’s empty threshold via UART_TXFIFO_EMPTY_THRHD;
  clearBits(C3_UART_CONF1_REG_UART0, 9, 9);

  // disable UART_TXFIFO_EMPTY_INT interrupt by clearing UART_TXFIFO_EMPTY_INT_ENA;
  clearBits(C3_UART_INT_ENA_REG_UART0, 1, 1);

  // write data to be sent to UART_RXFIFO_RD_BYTE;
  set_65_to_rd_byte();
  
  // clear UART_TXFIFO_EMPTY_INT interrupt by setting UART_TXFIFO_EMPTY_INT_CLR;
  setBit(C3_UART_INT_CLR_REG_UART0, 1)
  
  // enable UART_TXFIFO_EMPTY_INT interrupt by setting UART_TXFIFO_EMPTY_INT_ENA;
  setBit(C3_UART_INT_ENA_REG_UART0, 1)

  // detect UART_TXFIFO_EMPTY_INT and wait for the completion of data transmission.
}

void reset_uart(){
  // 26.4.1 Clock and Reset
  init_uart_enable_clk();
  init_uart_toggle_rst();
}

void init_uart(){
  // from technical reference manual 543 f
  init_uart_enable_clk();
  init_uart_toggle_rst();
  init_uart_clear_update();
}