mmu: Add initial implementation of identity mapping

kernel/Makefile.inc

@@ -5,5 +5,6 @@ KOBJS += $(KERNEL_PREFIX)/font.o
 KOBJS += $(KERNEL_PREFIX)/framebuffer.o
 KOBJS += $(KERNEL_PREFIX)/list.o
 KOBJS += $(KERNEL_PREFIX)/mm.o
+KOBJS += $(KERNEL_PREFIX)/mmu.o
 KOBJS += $(KERNEL_PREFIX)/print.o
 KOBJS += $(KERNEL_PREFIX)/start_kernel.o

kernel/mmu.c

@@ -0,0 +1,29 @@
+#include <print.h>
+
+#define SCTLR 15,0,1,0,0
+#define TTBR0 15,0,2,0,0
+#define TTBR1 15,0,2,0,1
+#define TTBCR 15,0,2,0,2
+
+#define _cp_read(var, cp, opc1, CRn, CRm, opc2) asm("mrc p" #cp ", " #opc1 ", %0, c" #CRn ", c" #CRm ", " #opc2 ";" : "=r"(var) : )
+#define _cp_write(var, cp, opc1, CRn, CRm, opc2) asm("mcr p" #cp ", " #opc1 ", %0, c" #CRn ", c" #CRm ", " #opc2 ";" : : "r"(var) )
+#define cp_read(var, ...)  _cp_read(var, __VA_ARGS__)
+#define cp_write(var, ...)  _cp_write(var, __VA_ARGS__)
+
+void mmu_reinit() {
+	unsigned int *curr_tt_entry; 
+	unsigned int curr_addr;
+
+	//get the current translation table base address
+	cp_read(curr_tt_entry, TTBR0);
+
+	//do first loop iteration outside the loop, because we have to check against wrapping back around to know we're done
+	*curr_tt_entry = 0xc02;
+	curr_tt_entry++;
+
+	//create identity mapping for entire address space using sections
+	for (curr_addr = 0x00100000; curr_addr != 0; curr_addr += 0x00100000) {
+		*curr_tt_entry = curr_addr | 0xc02;
+		curr_tt_entry++;
+	}
+}

kernel/start_kernel.c

@@ -1,3 +1,4 @@
+#include <mmu.h>
 #include <mm.h>
 #include <print.h>
 #include <devices/pl011.h>
@@ -54,6 +55,10 @@ void test_memory() {
  
 int main(void) {
 	char *lower;
+
+	//setup MMU
+	mmu_reinit();
+
 	print_init(&pl011_putc); //initialize the serial console
 
 	//setup memory