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/* SPDX-License-Identifier: GPL-2.0-only */
/* This file is part of the coreboot project. */
#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);
}
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