adding blinker02 example, uses lower part of the freerunning system level timer

blinker02/Makefile

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+
+ARMGNU ?= arm-none-eabi
+
+COPS = -Wall -O2 -nostdlib -nostartfiles -ffreestanding 
+
+all : kernel.img
+
+clean :
+	rm -f *.o
+	rm -f *.bin
+	rm -f *.elf
+	rm -f *.list
+	rm -f *.img
+
+novectors.o : novectors.s
+	$(ARMGNU)-as novectors.s -o novectors.o
+
+blinker02.o : blinker02.c
+	$(ARMGNU)-gcc $(COPS) -c blinker02.c -o blinker02.o
+
+kernel.img : memmap novectors.o blinker02.o 
+	$(ARMGNU)-ld novectors.o blinker02.o -T memmap -o blinker02.elf
+	$(ARMGNU)-objdump -D blinker02.elf > blinker02.list
+	$(ARMGNU)-objcopy blinker02.elf -O binary kernel.img
+
+
+
+
+
+

blinker02/README

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+
+See the top level README for information on where to find the
+schematic and programmers reference manual for the ARM processor
+on the raspberry pi.
+
+Based on some web searches the gpio is based at address 0x20200000 not
+0x7E200000 as shown in the documentation.  I have to go figure that out.
+
+There is a free-running 64 bit timer, super easy to use, just read it.
+
+Based on a couple of experiments, without messing with anything it
+appears that the timer is runing at about a megahertz, 1 million ticks
+per second.  I am guessing it is divided down from the 700MHz somewhere,
+will dig deeper.
+

blinker02/blinker02.c

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+
+//-------------------------------------------------------------------------
+//-------------------------------------------------------------------------
+
+extern void PUT32 ( unsigned int, unsigned int );
+extern unsigned int GET32 ( unsigned int );
+extern void dummy ( unsigned int );
+
+#define SYSTIMERCLO 0x20003004
+#define GPFSEL1 0x20200004
+#define GPSET0  0x2020001C
+#define GPCLR0  0x20200028
+
+//-------------------------------------------------------------------------
+int notmain ( void )
+{
+    unsigned int ra;
+
+    ra=GET32(GPFSEL1);
+    ra&=~(7<<18);
+    ra|=1<<18;
+    PUT32(GPFSEL1,ra);
+
+    while(1)
+    {
+        PUT32(GPSET0,1<<16);
+        while(1)
+        {
+            ra=GET32(SYSTIMERCLO);
+            //0x01000000 17 seconds
+            if((ra&=0x01000000)==0x01000000) break;
+            //0x00400000 4 seconds
+            if((ra&=0x00400000)==0x01000000) break;
+        }
+        PUT32(GPCLR0,1<<16);
+        while(1)
+        {
+            ra=GET32(SYSTIMERCLO);
+            //if((ra&=0x01000000)==0x00000000) break;
+            if((ra&=0x00400000)==0x00000000) break;
+        }
+    }
+    return(0);
+}
+//-------------------------------------------------------------------------
+//-------------------------------------------------------------------------

blinker02/memmap

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+
+MEMORY
+{
+    ram : ORIGIN = 0x00000000, LENGTH = 0x1000
+}
+
+SECTIONS
+{
+    .text : { *(.text*) } > ram
+    .bss : { *(.bss*) } > ram
+}
+

blinker02/novectors.s

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+
+.globl _start
+_start:
+    b reset
+
+reset:
+    mov sp,#0x1000
+    bl notmain
+hang: b hang
+
+.globl PUT32
+PUT32:
+    str r1,[r0]
+    bx lr
+
+.globl GET32
+GET32:
+    ldr r0,[r0]
+    bx lr
+
+.globl dummy
+dummy:
+    bx lr