Using the mmu in a much simpler way (sections instead of pages) after…

… doing

the mmu example.

Not sure how this worked before it was set for an address of 0 not 0x8000

extest/Makefile

@@ -1,7 +1,7 @@
 
 
 
-ARMGNU ?= arm-none-linux-gnueabi
+ARMGNU ?= arm-linux-gnueabi
 
 COPS = -Wall -O2 -nostdlib -nostartfiles -ffreestanding 
 
@@ -11,6 +11,7 @@ clean :
 	rm -f *.o
 	rm -f *.bin
 	rm -f *.elf
+	rm -f *.hex
 	rm -f *.list
 
 vectors.o : vectors.s
@@ -25,6 +26,7 @@ uart.o : uart.c
 notmain.bin : memmap vectors.o uart.o notmain.o 
 	$(ARMGNU)-ld -T memmap vectors.o notmain.o uart.o -o notmain.elf
 	$(ARMGNU)-objdump -D notmain.elf > notmain.list
+	$(ARMGNU)-objcopy notmain.elf -O ihex notmain.hex 
 	$(ARMGNU)-objcopy notmain.elf -O binary notmain.bin 
 
 

extest/memmap

@@ -1,7 +1,7 @@
 
 MEMORY
 {
-    ram : ORIGIN = 0x00000000, LENGTH = 0x10000
+    ram : ORIGIN = 0x00008000, LENGTH = 0x10000
 }
 
 SECTIONS

extest/notmain.c

@@ -13,95 +13,21 @@ extern unsigned int LDREX ( unsigned int, unsigned int );
 extern unsigned int STREX ( unsigned int, unsigned int, unsigned int );
 extern unsigned int EXTEST ( unsigned int, unsigned int, unsigned int );
 
-//Need a top level entry for every 1MB section, 20 bits.
-//memory base addresses 0x100000, 0x200000, 0x300000, etc.
-//making a one to one virtual to physical map
-//virtual 0x20201234 -> 0x20201234 physical
-//
-//bits 31:20 of the virtual address index into the top level table
-//1<<((31-20)+1)  4096 entries. 0x1000 32 bit entries, 0x4000 bytes.
-//
-//Bits 31:10 of the top level table point at the course page table
-//bits 19:12 of the address index into this table.
-//1<<((19-12)+1)  256 entries, 0x100 entries 0x400 bytes per entry
-//
-//Using a course entry
-//
-//the hardware looks in the first table and gets an entry.  Bits in the
-//entry determine what kind it is, course, section, super section,
-//just using course here as it doesnt save any space using the others.
-//You can put the coarse entry anywhere.  Going to pack it in next to
-//the top level table.  going to limit the size of the table so only
-//so many entries will be allowed
-//
-//Using small pages (4096 byte)
-//
-//bits 31:12 of the small page descriptor in the course table are the
-//physical address in memory.  bits 11:0 of the physical address come
-//from the virtual address.
-
 #define MMUTABLEBASE 0x00100000
 
-#define MMUTABLESIZE (0x8000)
-#define MMUTABLEMASK ((MMUTABLESIZE-1)>>2)
-
-#define TOP_LEVEL_WORDS (1<<((31-20)+1))
-#define COARSE_TABLE_WORDS (1<<((19-12)+1))
-#define SMALL_TABLE_WORDS (1<<((11-0)+1))
-
-unsigned int nextfree;
-
-//-------------------------------------------------------------------
-unsigned int next_coarse_offset ( unsigned int x )
-{
-    unsigned int mask;
-
-    mask=(~0)<<(10-2);
-    mask=~mask;
-    while(x&mask) x++; //lazy brute force
-    return(x);
-}
 //-------------------------------------------------------------------
-unsigned int add_one ( unsigned int add, unsigned int flags )
+unsigned int mmu_section ( unsigned int add, unsigned int flags )
 {
     unsigned int ra;
     unsigned int rb;
     unsigned int rc;
 
-    //bits 31:20 index into the top level table
     ra=add>>20;
-    rc=MMUTABLEBASE+(ra<<2);
-    rb=GET32(rc);
-    if(rb)
-    {
-        //printf("Address %08X already allocated\n",add);
-        hexstring(add);
-        hexstring(rc);
-        hexstring(rb);
-        hexstring(0xBADADD);
-        return(1);
-    }
-    add=ra<<20;
-
-    rb=next_coarse_offset(nextfree);
-    rc=rb+COARSE_TABLE_WORDS;
-    if(rc>=MMUTABLESIZE)
-    {
-        //printf("Not enough room\n");
-        hexstring(0xBAD);
-        return(1);
-    }
-    nextfree=rc;
-    //use course page table pointer on top level table
-    PUT32(MMUTABLEBASE+(ra<<2),(MMUTABLEBASE+(rb<<2))|0x00000001);
-    //fill in the course page table. with small entries
-    for(ra=0;ra<COARSE_TABLE_WORDS;ra++)
-    {
-        PUT32(MMUTABLEBASE+(rb<<2)+(ra<<2),(add+(ra<<12))|0x00000032|flags);
-    }
+    rb=MMUTABLEBASE|(ra<<2);
+    rc=(ra<<20)|flags|2;
+    PUT32(rb,rc);
     return(0);
 }
-
 //-------------------------------------------------------------------------
 int notmain ( void )
 {
@@ -113,15 +39,12 @@ int notmain ( void )
 
     hexstring(0x12345678);
 
-    for(nextfree=0;nextfree<TOP_LEVEL_WORDS;nextfree++) PUT32(MMUTABLEBASE+(nextfree<<2),0);
-    //nextfree=TOP_LEVEL_WORDS;
-
     //ram used by the stack and the program
-    if(add_one(0x00000000,0x0000|8|4)) return(1);
+    if(mmu_section(0x00000000,0x0000|8|4)) return(1);
     //Memory mapped I/O used by the uart, etc, not cached
-    if(add_one(0x20000000,0x0000)) return(1);
-    if(add_one(0x20100000,0x0000)) return(1);
-    if(add_one(0x20200000,0x0000)) return(1);
+    if(mmu_section(0x20000000,0x0000)) return(1);
+    if(mmu_section(0x20100000,0x0000)) return(1);
+    if(mmu_section(0x20200000,0x0000)) return(1);
 
     //not enabling data cache just yet.
     start_mmu(MMUTABLEBASE,0x00800001);

extest/vectors.s

@@ -50,6 +50,7 @@ start_l1cache:
     mov r0, #0
     mcr p15, 0, r0, c7, c7, 0 ;@ invalidate caches
     mcr p15, 0, r0, c8, c7, 0 ;@ invalidate tlb
+    mcr p15, 0, r2, c7,c10, 4 ;@ DSB ??
     mrc p15, 0, r0, c1, c0, 0
     orr r0,r0,#0x1000 ;@ instruction
     orr r0,r0,#0x0004 ;@ data