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/***************************************************************************
* Copyright (c) 2024 Microsoft Corporation
* Copyright (c) 2026-present Eclipse ThreadX contributors
*
* This program and the accompanying materials are made available under the
* terms of the MIT License which is available at
* https://opensource.org/licenses/MIT.
*
* SPDX-License-Identifier: MIT
**************************************************************************/
/* NS16550-compatible UART driver for QEMU virt machine (RV32 and RV64). */
#include "uart.h"
#include "csr.h"
#include "plic.h"
#include <stdint.h>
/* Memory-mapped UART control registers. */
#define Reg(reg) ((volatile unsigned char *)(UART0 + (reg)))
#define RHR 0 /* receive holding register (for input bytes) */
#define THR 0 /* transmit holding register (for output bytes) */
#define IER 1 /* interrupt enable register */
#define IER_RX_ENABLE (1<<0)
#define IER_TX_ENABLE (1<<1)
#define FCR 2 /* FIFO control register */
#define FCR_FIFO_ENABLE (1<<0)
#define FCR_FIFO_CLEAR (3<<1) /* clear the content of the two FIFOs */
#define ISR 2 /* interrupt status register */
#define LCR 3 /* line control register */
#define LCR_EIGHT_BITS (3<<0)
#define LCR_BAUD_LATCH (1<<7) /* special mode to set baud rate */
#define LSR 5 /* line status register */
#define LSR_RX_READY (1<<0) /* input is waiting to be read from RHR */
#define LSR_TX_IDLE (1<<5) /* THR can accept another character to send */
#define ReadReg(reg) (*(Reg(reg)))
#define WriteReg(reg, v) (*(Reg(reg)) = (v))
int uart_init(void)
{
/* Disable interrupts. */
WriteReg(IER, 0x00);
/* Special mode to set baud rate. */
WriteReg(LCR, LCR_BAUD_LATCH);
/* LSB for baud rate of 38.4K. */
WriteReg(0, 0x03);
/* MSB for baud rate of 38.4K. */
WriteReg(1, 0x00);
/* Leave set-baud mode, set word length to 8 bits, no parity. */
WriteReg(LCR, LCR_EIGHT_BITS);
/* Reset and enable FIFOs. */
WriteReg(FCR, FCR_FIFO_ENABLE | FCR_FIFO_CLEAR);
/* Enable UART0 in PLIC. */
plic_irq_enable(UART0_IRQ);
/* Set UART0 priority in PLIC. */
plic_prio_set(UART0_IRQ, 1);
puts("[UART0] : Uart Init Done, this is Test output!");
return 0;
}
/* uart_putc_nolock is static inline so it can be inlined into uart_putc
and uart_puts without introducing a public symbol. */
static inline void uart_putc_nolock(int ch)
{
while ((ReadReg(LSR) & LSR_TX_IDLE) == 0)
;
WriteReg(THR, ch);
}
int uart_putc(int ch)
{
int intr_enable = riscv_mintr_get();
riscv_mintr_off();
uart_putc_nolock(ch);
riscv_mintr_restore(intr_enable);
return 1;
}
int uart_puts(const char *str)
{
int i;
int intr_enable = riscv_mintr_get();
riscv_mintr_off();
for (i = 0; str[i] != 0; i++)
uart_putc_nolock(str[i]);
uart_putc_nolock('\n');
riscv_mintr_restore(intr_enable);
return i;
}
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