move stuff around

Makefile

@@ -1,18 +1,22 @@
-CC	:= $(PREFIX)gcc
-AS	:= $(PREFIX)as
-OBJCPY	:= $(PREFIX)objcopy
+CC		:= $(PREFIX)gcc
+AS		:= $(PREFIX)as
+OBJCPY		:= $(PREFIX)objcopy
+boot.o: src/boot.S
+	$(AS) -c src/boot.S -o boot.o
 
-boot.o: boot.S
-	$(AS) -c boot.S -o boot.o
+kernel.o: src/kernel.c
+	$(CC) -ffreestanding -c src/kernel.c -o kernel.o -O2 -Wall -Wextra
+
+os.elf: boot.o kernel.o src/linker.ld
+	$(CC) -T src/linker.ld -o os.elf -ffreestanding -O2 -nostdlib boot.o kernel.o -lgcc
 
-kernel.o: kernel.c
-	$(CC) -ffreestanding -c kernel.c -o kernel.o -O2 -Wall -Wextra
-	
-os.elf: boot.o kernel.o linker.ld
-	$(CC) -T linker.ld -o os.elf -ffreestanding -O2 -nostdlib boot.o kernel.o -lgcc
-	
 kernel8.img: os.elf
 	$(OBJCPY) os.elf -O binary kernel8.img
 
+.PHONY: image kernel
+image: kernel8.img
+
+kernel: os.elf
+
 clean:
 	rm boot.o kernel.o os.elf kernel8.img

src/kernel.c

@@ -1,5 +1,7 @@
 #include <stddef.h>
 #include <stdint.h>
+#include "mmio.h"
+#include "uart.h"
 
 volatile uint64_t** core_1 = (void*)0xE0;
 volatile uint64_t** core_2 = (void*)0xE8;
@@ -21,6 +23,25 @@ void _start_core_3(void* addr) {
 }
 
 
+
 void kernel_main(uint64_t dtb_ptr32, uint64_t x1, uint64_t x2, uint64_t x3) {
+    uint32_t reg;
+    char *board;
+
+    asm volatile ("mrs %x0, midr_el1" : "=r" (reg));
+
+    switch ((reg >> 4) & 0xFFF) {
+        case 0xD03:
+            board = "Raspberry Pi 3";
+            MMIO_BASE = 0x3F000000;
+            break;
+        case 0xD08:
+            board = "Raspberry Pi 4";
+            MMIO_BASE = 0xFE000000;
+            break;
+    }
+    uart_init();
+    uart_puts(board);
+
     return;
 }

src/mmio.h

@@ -0,0 +1,22 @@
+#ifndef MMIO_H
+#define MMIO_H
+
+static uint32_t MMIO_BASE;
+
+static inline void mmio_write(uint32_t reg, uint32_t data)
+{
+	*(volatile uint32_t*)(MMIO_BASE + reg) = data;
+}
+
+
+static inline uint32_t mmio_read(uint32_t reg)
+{
+	return *(volatile uint32_t*)(MMIO_BASE + reg);
+}
+
+static inline void delay(int32_t count)
+{
+	asm volatile("__delay_%=: subs %[count], %[count], #1; bne __delay_%=\n"
+		 : "=r"(count): [count]"0"(count) : "cc");
+}
+#endif

src/uart.h

@@ -0,0 +1,119 @@
+#ifndef UART_H
+#define UART_H
+#include "mmio.h"
+
+enum
+{
+    // The offsets for reach register.
+    GPIO_BASE = 0x200000,
+
+    // Controls actuation of pull up/down to ALL GPIO pins.
+    GPPUD = (GPIO_BASE + 0x94),
+
+    // Controls actuation of pull up/down for specific GPIO pin.
+    GPPUDCLK0 = (GPIO_BASE + 0x98),
+
+    // The base address for UART.
+    UART0_BASE = (GPIO_BASE + 0x1000), // for raspi4 0xFE201000, raspi2 & 3 0x3F201000, and 0x20201000 for raspi1
+
+    // The offsets for reach register for the UART.
+    UART0_DR     = (UART0_BASE + 0x00),
+    UART0_RSRECR = (UART0_BASE + 0x04),
+    UART0_FR     = (UART0_BASE + 0x18),
+    UART0_ILPR   = (UART0_BASE + 0x20),
+    UART0_IBRD   = (UART0_BASE + 0x24),
+    UART0_FBRD   = (UART0_BASE + 0x28),
+    UART0_LCRH   = (UART0_BASE + 0x2C),
+    UART0_CR     = (UART0_BASE + 0x30),
+    UART0_IFLS   = (UART0_BASE + 0x34),
+    UART0_IMSC   = (UART0_BASE + 0x38),
+    UART0_RIS    = (UART0_BASE + 0x3C),
+    UART0_MIS    = (UART0_BASE + 0x40),
+    UART0_ICR    = (UART0_BASE + 0x44),
+    UART0_DMACR  = (UART0_BASE + 0x48),
+    UART0_ITCR   = (UART0_BASE + 0x80),
+    UART0_ITIP   = (UART0_BASE + 0x84),
+    UART0_ITOP   = (UART0_BASE + 0x88),
+    UART0_TDR    = (UART0_BASE + 0x8C),
+
+    // The offsets for Mailbox registers
+    MBOX_BASE    = 0xB880,
+    MBOX_READ    = (MBOX_BASE + 0x00),
+    MBOX_STATUS  = (MBOX_BASE + 0x18),
+    MBOX_WRITE   = (MBOX_BASE + 0x20)
+};
+
+volatile unsigned int  __attribute__((aligned(16))) mbox[9] = {
+    9*4, 0, 0x38002, 12, 8, 2, 3000000, 0 ,0
+};
+
+void uart_init()
+{
+	mmio_write(UART0_CR, 0x00000000);
+	// Setup the GPIO pin 14 && 15.
+ 
+	// Disable pull up/down for all GPIO pins & delay for 150 cycles.
+	mmio_write(GPPUD, 0x00000000);
+	delay(150);
+ 
+	// Disable pull up/down for pin 14,15 & delay for 150 cycles.
+	mmio_write(GPPUDCLK0, (1 << 14) | (1 << 15));
+	delay(150);
+ 
+	// Write 0 to GPPUDCLK0 to make it take effect.
+	mmio_write(GPPUDCLK0, 0x00000000);
+ 
+	// Clear pending interrupts.
+	mmio_write(UART0_ICR, 0x7FF);
+ 
+	// Set integer & fractional part of baud rate.
+	// Divider = UART_CLOCK/(16 * Baud)
+	// Fraction part register = (Fractional part * 64) + 0.5
+	// Baud = 115200.
+
+	// For Raspi3 and 4 the UART_CLOCK is system-clock dependent by default.
+	// Set it to 3Mhz so that we can consistently set the baud rate
+	unsigned int r = (((unsigned int)(&mbox) & ~0xF) | 8);
+	// wait until we can talk to the VC
+	while ( mmio_read(MBOX_STATUS) & 0x80000000 ) { }
+	// send our message to property channel and wait for the response
+	mmio_write(MBOX_WRITE, r);
+	while ( (mmio_read(MBOX_STATUS) & 0x40000000) || mmio_read(MBOX_READ) != r ) { }
+
+	// Divider = 3000000 / (16 * 115200) = 1.627 = ~1.
+	mmio_write(UART0_IBRD, 1);
+	// Fractional part register = (.627 * 64) + 0.5 = 40.6 = ~40.
+	mmio_write(UART0_FBRD, 40);
+
+	// Enable FIFO & 8 bit data transmission (1 stop bit, no parity).
+	mmio_write(UART0_LCRH, (1 << 4) | (1 << 5) | (1 << 6));
+
+	// Mask all interrupts.
+	mmio_write(UART0_IMSC, (1 << 1) | (1 << 4) | (1 << 5) | (1 << 6) |
+	                       (1 << 7) | (1 << 8) | (1 << 9) | (1 << 10));
+
+	// Enable UART0, receive & transfer part of UART.
+	mmio_write(UART0_CR, (1 << 0) | (1 << 8) | (1 << 9));
+}
+
+void uart_putc(unsigned char c)
+{
+	// Wait for UART to become ready to transmit.
+	while ( mmio_read(UART0_FR) & (1 << 5) ) { }
+	mmio_write(UART0_DR, c);
+}
+ 
+unsigned char uart_getc()
+{
+    // Wait for UART to have received something.
+    while ( mmio_read(UART0_FR) & (1 << 4) ) { }
+    return mmio_read(UART0_DR);
+}
+ 
+void uart_puts(const char* str)
+{
+	for (size_t i = 0; str[i] != '\0'; i ++)
+		uart_putc((unsigned char)str[i]);
+}
+
+#endif