/* * This file is part of the coreboot project. * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation; version 2 of the License. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. */ #include <console/console.h> #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 !IS_ENABLED(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 !IS_ENABLED(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); }