util.c

Go to the documentation of this file.

/* SPDX-License-Identifier: GPL-2.0-only */
 
#include <console/uart.h>
#include <types.h>
#include <timer.h>
 
/* Calculate divisor. Do not floor but round to nearest integer. */
unsigned int uart_baudrate_divisor(unsigned int baudrate,
        unsigned int refclk, unsigned int oversample)
{
        return (1 + (2 * refclk) / (baudrate * oversample)) / 2;
}
 
#if !CONFIG(UART_OVERRIDE_INPUT_CLOCK_DIVIDER)
unsigned int uart_input_clock_divider(void)
{
        /* Specify the default oversample rate for the UART.
         *
         * UARTs oversample the receive data.  The UART's input clock first
         * enters the baud-rate divider to generate the oversample clock.  Then
         * the UART typically divides the result by 16.  The asynchronous
         * receive data is synchronized with the oversample clock and when a
         * start bit is detected the UART delays half a bit time using the
         * oversample clock.  Samples are then taken to verify the start bit and
         * if present, samples are taken for the rest of the frame.
         */
        return 16;
}
#endif
 
#if !CONFIG(UART_OVERRIDE_REFCLK)
unsigned int uart_platform_refclk(void)
{
        /* Specify the default input clock frequency for the UART.
         *
         * The older UART's used an input clock frequency of 1.8432 MHz which
         * with the 16x oversampling provided the maximum baud-rate of 115200.
         * Specify this as maximum baud-rate multiplied by oversample so that
         * it is obvious that the maximum baud rate is 115200 when divided by
         * oversample clock.  Also note that crystal on the board does not
         * change when software selects another input clock divider.
         */
        return 115200 * 16;
}
#endif
 
/* Helper function to allow bitbanging an 8n1 UART. */
void uart_bitbang_tx_byte(unsigned char data, void (*set_tx)(int line_state))
{
        const int baud_rate = get_uart_baudrate();
        int i;
        struct stopwatch sw;
        stopwatch_init(&sw);
 
        /* Send start bit */
        set_tx(0);
        while (stopwatch_duration_usecs(&sw) < MHz / baud_rate)
                stopwatch_tick(&sw);
 
        /* 'i' counts the total bits sent at the end of the loop */
        for (i = 2; i < 10; i++) {
                set_tx(data & 1);
                data >>= 1;
                while (stopwatch_duration_usecs(&sw) < i * MHz / baud_rate)
                        stopwatch_tick(&sw);
        }
 
        /* Send stop bit */
        set_tx(1);
        while (stopwatch_duration_usecs(&sw) < i * MHz / baud_rate)
                stopwatch_tick(&sw);
}