adding blinker03 example uses the ARM freerunning timer

blinker03/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
+
+blinker03.o : blinker03.c
+	$(ARMGNU)-gcc $(COPS) -c blinker03.c -o blinker03.o
+
+kernel.img : memmap novectors.o blinker03.o 
+	$(ARMGNU)-ld novectors.o blinker03.o -T memmap -o blinker03.elf
+	$(ARMGNU)-objdump -D blinker03.elf > blinker03.list
+	$(ARMGNU)-objcopy blinker03.elf -O binary kernel.img
+
+
+
+
+
+

blinker03/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.
+
+This example uses the free running ARM timer, not the 64 bit system
+one as in blinker02 but the so called ARM timer.
+
+The system clock appears to come up at 250MHz as documented.  Divide that
+by 250 to get 1Mhz on this free running ARM timer.  Then count to four
+million ticks between led state changes and the led will change state
+every four seconds.

blinker03/blinker03.c

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+
+//-------------------------------------------------------------------------
+//-------------------------------------------------------------------------
+
+extern void PUT32 ( unsigned int, unsigned int );
+extern unsigned int GET32 ( unsigned int );
+extern void dummy ( unsigned int );
+
+#define ARM_TIMER_LOD 0x2000B400
+#define ARM_TIMER_VAL 0x2000B404
+#define ARM_TIMER_CTL 0x2000B408
+#define ARM_TIMER_DIV 0x2000B41C
+#define ARM_TIMER_CNT 0x2000B420
+
+#define SYSTIMERCLO 0x20003004
+#define GPFSEL1 0x20200004
+#define GPSET0  0x2020001C
+#define GPCLR0  0x20200028
+
+//From experiments and from the manual the freerunning ARM timer is
+//not affected by the timer enable bit.  Not affected by the 0x41C
+//prescaler.  Not affected by bits 3:2 of the control register.
+//And is affected by bits 23:16 of the control register.
+
+//It still appears as if the system timer is 250Mhz as mentioned somewhere
+//in the manual (starts up at 250MHz).
+//If we divide 250MHz/250 we can make the free running clock 1mhz
+//wait for 4 million ticks and the led will change state every 4 seconds
+//Note the free running timer is an up counting timer, the other arm
+//timer is a down counter.
+
+#define TIMEOUT 4000000
+
+
+//-------------------------------------------------------------------------
+int notmain ( void )
+{
+    unsigned int ra;
+    unsigned int rb;
+
+    ra=GET32(GPFSEL1);
+    ra&=~(7<<18);
+    ra|=1<<18;
+    PUT32(GPFSEL1,ra);
+
+    PUT32(ARM_TIMER_CTL,0x00F90000);
+    PUT32(ARM_TIMER_CTL,0x00F90200);
+
+    rb=GET32(ARM_TIMER_CNT);
+    while(1)
+    {
+        PUT32(GPSET0,1<<16);
+        while(1)
+        {
+            ra=GET32(ARM_TIMER_CNT);
+            if((ra-rb)>=TIMEOUT) break;
+        }
+        rb+=TIMEOUT;
+        PUT32(GPCLR0,1<<16);
+        while(1)
+        {
+            ra=GET32(ARM_TIMER_CNT);
+            if((ra-rb)>=TIMEOUT) break;
+        }
+        rb+=TIMEOUT;
+    }
+    return(0);
+}
+//-------------------------------------------------------------------------
+//-------------------------------------------------------------------------

blinker03/memmap

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

blinker03/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