ptos/amd64: platform: Add UART driver + HAL interface

Signed-off-by: Chloe M. <chloe@yiffware.org>

service/ptos/arch/amd64/platform/uart.c

@@ -0,0 +1,105 @@
+/*
+ * Copyright (c) 2026, Chloe M.
+ * Provided under the BSD-3 clause.
+ *
+ * Description: UART driver
+ * Author:      Chloe M.
+ */
+
+#include <hal/serial.h>
+#include <machine/pio.h>
+#include <ptdef.h>
+
+/* Channel port numbers */
+#define UART_COM1 0x3F8
+#define UART_COM2 0x2F8
+#define UART_COM3 0x3E8
+#define UART_COM4 0x2E8
+#define UART_COM5 0x5F8
+#define UART_COM6 0x4F8
+#define UART_COM7 0x5E8
+#define UART_COM8 0x4E8
+
+/* Register offsets */
+#define UART_REG(OFFSET) (UART_COM1 + OFFSET)
+#define UART_REG_FCR UART_REG(2) /* FIFO Control Register */
+#define UART_REG_LCR UART_REG(3) /* Line Control Register */
+#define UART_REG_MCR UART_REG(4) /* MODEM Control Register */
+#define UART_REG_LSR UART_REG(5) /* Line Status Register */
+#define UART_REG_MSR UART_REG(6) /* MODEM Status Register */
+#define UART_REG_SR  UART_REG(7) /* Scratch Register */
+
+/* Registers when LCR.DLAB=0 */
+#define UART_REG_RBR UART_REG(0) /* Receiver Buffer Register */
+#define UART_REG_THR UART_REG(0) /* Transmitter Holding Register */
+#define UART_REG_IER UART_REG(1) /* Interrupt Enable Register */
+
+/* Registers when LCR.DLAB=1 */
+#define UART_REG_DLL UART_REG(0) /* Divisor Latch Low */
+#define UART_REG_DLH UART_REG(1) /* Divisor Latch High */
+
+#define UART_LCR_WLS0 BIT(0) /* Word Length Select Bit 0 */
+#define UART_LCR_WLS1 BIT(1) /* Word Length Select Bit 1 */
+#define UART_LCR_DLAB BIT(7) /* Divisor Latch Access Bit*/
+
+#define UART_MCR_DTR  BIT(0) /* Data Terminal Ready*/
+#define UART_MCR_LOOP BIT(4) /* Loop */
+
+#define UART_LSR_THRE BIT(5) /* Transmitter Holding Register */
+
+#define UART_DIVISOR(RATE) (115200 / RATE)
+
+static inline BOOLEAN
+UartTxEmpty(VOID)
+{
+    return ISSET(UART_REG_LSR, UART_LSR_THRE) != 0;
+}
+
+VOID
+HalSerialWrite(const CHAR *Data, USIZE Length)
+{
+    if (Data == NULL) {
+        return;
+    }
+
+    while (!UartTxEmpty()) {
+        ASMV("pause");
+    }
+
+    for (USIZE Index = 0; Index < Length; ++Index) {
+        MdOutb(UART_REG_THR, Data[Index]);
+    }
+}
+
+PT_STATUS
+HalSerialInit(VOID)
+{
+    /* Disable interrupts */
+    MdOutb(UART_REG_IER, 0x00);
+
+    /* Set DLAB to set baud rate */
+    MdOutb(UART_REG_LCR, UART_LCR_DLAB);
+
+    /* Set speed to 57600 baud */
+    MdOutb(UART_REG_DLL, UART_DIVISOR(57600));
+    MdOutb(UART_REG_IER, 0x00);
+
+    /* Set word size to 8 bits and clear DLAB */
+    MdOutb(UART_REG_LCR, UART_LCR_WLS0 | UART_LCR_WLS1);
+
+    /* Disable FIFOs for now... (TODO: Use them) */
+    MdOutb(UART_REG_FCR, 0x00);
+
+    /* Test chip in loopback mode */
+    MdOutb(UART_REG_MCR, UART_MCR_LOOP);
+    MdOutb(UART_REG_THR, 0xF0);
+    if (MdInb(UART_REG_RBR != 0xF0))
+        return -1;
+
+    /*
+     * Mark the data terminal ready and clear
+     * loopback mode.
+     */
+    MdOutb(UART_REG_MCR, UART_MCR_DTR);
+    return 0;
+}

service/ptos/head/hal/serial.h

@@ -0,0 +1,27 @@
+/*
+ * Copyright (c) 2026, Chloe M.
+ * Provided under the BSD-3 clause.
+ *
+ * Description: HAL serial interface
+ * Author:      Chloe M.
+ */
+
+#ifndef _HAL_SERIAL_H_
+#define _HAL_SERIAL_H_ 1
+
+#include <ptapi/status.h>
+
+/*
+ * Initialize the serial driver
+ */
+PT_STATUS HalSerialInit(VOID);
+
+/*
+ * Transmit data over serial
+ *
+ * @Data:   Data to transmit
+ * @Length: Length of data to transmit
+ */
+VOID HalSerialWrite(const CHAR *Data, USIZE Length);
+
+#endif  /* !_HAL_SERIAL_H_ */

service/ptos/ke/init.c

@@ -8,6 +8,7 @@
 
 #include <ptdef.h>
 #include <ke/bpal.h>
+#include <hal/serial.h>
 #include <machine/pio.h>
 #include <string.h>
 
@@ -20,4 +21,7 @@ KiKernelInit(VOID)
 {
     /* Initialize the boot protocol abstraction layer */
     KeBpalInit();
+
+    /* Initialize the serial driver */
+    HalSerialInit();
 }