The start of the project -- A MicroDOS

feat: Initial bare-metal RISC-V boot with UART

3 files changed, 105 insertions, 0 deletions

diff --git a/src/boot/entry.S b/src/boot/entry.S
new file mode 100644
index 0000000..1a6f6b8
--- /dev/null
+++ b/src/boot/entry.S
@@ -0,0 +1,28 @@
+.section .text.entry
+.globl _start
+
+_start:
+    csrr t0, mhartid
+    bnez t0, .L_park_harts
+
+    la sp, _stack_top
+
+    la a0, _bss_start
+    la a1, _bss_end
+    bge a0, a1, .L_call_main
+
+.L_clear_bss:
+    sd zero, (a0)
+    addi a0, a0, 8
+    blt a0, a1, .L_clear_bss
+
+.L_call_main:
+    call kernel_main
+
+.L_infinite_loop:
+    wfi
+    j .L_infinite_loop
+
+.L_park_harts:
+    wfi
+    j .L_park_harts
\ No newline at end of file
diff --git a/src/drivers/uart.cc b/src/drivers/uart.cc
new file mode 100644
index 0000000..758abd9
--- /dev/null
+++ b/src/drivers/uart.cc
@@ -0,0 +1,57 @@
+#include "drivers/uart.h"
+#include "common/types.h"
+
+#define UART0_BASE          0x10000000L
+
+#define UART_RBR            0x00 // Receiver Buffer Register (Read)
+#define UART_THR            0x00 // Transmitter Holding Register (Write)
+#define UART_IER            0x01 // Interrupt Enable Register
+#define UART_FCR            0x02 // FIFO Control Register
+#define UART_LCR            0x03 // Line Control Register
+#define UART_LSR            0x05 // Line Status Register
+
+#define UART_LSR_RX_READY   0x01
+#define UART_LSR_TX_EMPTY   0x20
+
+namespace Drivers{
+    inline volatile uint8_t &reg(uint32_t offset)
+    {
+        return *reinterpret_cast<volatile uint8_t *>(UART0_BASE + offset);
+    }
+
+    void uart_init()
+    {
+        reg(UART_IER) = 0x00;
+
+        reg(UART_LCR) = 0x80;
+        reg(0x00) = 0x03;
+        reg(0x01) = 0x00;
+
+        reg(UART_LCR) = 0x03;
+
+        reg(UART_FCR) = 0x07; // Enable FIFO, clear TX/RX queues
+    }
+
+    void uart_putc(char c)
+    {
+        if (c == '\n')
+        {
+            uart_putc('\r');
+        }
+
+        while ((reg(UART_LSR) & UART_LSR_TX_EMPTY) == 0)
+        {
+
+        }
+
+        reg(UART_THR) = c;
+    }
+
+    void uart_puts(const char *s)
+    {
+        while (*s)
+        {
+            uart_putc(*s++);
+        }
+    }
+}
\ No newline at end of file
diff --git a/src/kernel/main.cc b/src/kernel/main.cc
new file mode 100644
index 0000000..49adf2b
--- /dev/null
+++ b/src/kernel/main.cc
@@ -0,0 +1,20 @@
+#include "drivers/uart.h"
+
+extern "C" void kernel_main()
+{
+
+    Drivers::uart_init();
+
+    Drivers::uart_puts("\n");
+    Drivers::uart_puts("Modern DOS v1.0 [RISC-V 64]\n");
+    Drivers::uart_puts("2025 Richard Qin\n");
+    Drivers::uart_puts("\n");
+
+    Drivers::uart_puts("A:\\> ");
+
+
+    while (1)
+    {
+
+    }
+}
\ No newline at end of file