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/*
* Copyright (c) 2025 Ian Marco Moffett and L5 engineers
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* 1. Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. Neither the name of the project nor the names of its
* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/
#include <sys/param.h>
#include <sys/types.h>
#include <machine/uart.h>
#include <machine/pio.h>
static inline uint8_t
uart_transmit_empty(void)
{
return ISSET(UART_REG_LSR, UART_LSR_THRE);
}
void
uart_write(char byte)
{
while (!uart_transmit_empty());
outb(UART_REG_THR, byte);
}
int
uart_init(void)
{
/* Disable interrupts */
outb(UART_REG_IER, 0x00);
/* Set DLAB to set baud rate */
outb(UART_REG_LCR, UART_LCR_DLAB);
/* Set speed to 57600 baud */
outb(UART_REG_DLL, UART_DIVISOR(57600));
outb(UART_REG_IER, 0x00);
/* Set word size to 8 bits and clear DLAB */
outb(UART_REG_LCR, UART_LCR_WLS0 | UART_LCR_WLS1);
/* Disable FIFOs for now... (TODO: Use them) */
outb(UART_REG_FCR, 0x00);
/* Test chip in loopback mode */
outb(UART_REG_MCR, UART_MCR_LOOP);
outb(UART_REG_THR, 0xF0);
if (inb(UART_REG_RBR != 0xF0)) {
return -1;
}
/*
* Mark the data terminal ready and clear
* loopback mode.
*/
outb(UART_REG_MCR, UART_MCR_DTR);
return 0;
}
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