I would like to comprehend lesson 2 of Baking Pi, but I am not able to get the LED blinking.
I am using Windows and have installed Cygwin and the ARM tool chain. As explained in the requirements, I have downloaded the latest Raspbian, which works fine. I was able to use the serial cable with Putty to login and to do a apt-get update && apt-get dist-upgrade.
Now I downloaded the lesson 2 code and compiled it, which works also fine.
~/Downloads/ok02$ make arm-none-eabi-as -I source/ source/main.s -o build/main.o arm-none-eabi-ld --no-undefined build/main.o -Map kernel.map -o build/output.elf -T kernel.ld arm-none-eabi-objcopy build/output.elf -O binary kernel.img arm-none-eabi-objdump -d build/output.elf > kernel.list
I have renamed the original kernel and copied the new kernel.img file to the SD card.
~/Downloads/ok02$ ls -l /cygdrive/l total 9856 -rw-r--r-- 1 Sascha None 18974 Sep 25 2013 LICENSE.oracle -rw-r--r-- 1 Sascha None 17840 Sep 8 21:24 bootcode.bin -rw-r--r-- 1 Sascha None 120 Sep 8 22:26 cmdline.txt -rw-r--r-- 1 Sascha None 265 Dec 24 11:00 config.txt -rw-r--r-- 1 Sascha None 6115 Sep 8 21:24 fixup.dat -rw-r--r-- 1 Sascha None 2324 Sep 8 21:24 fixup_cd.dat -rw-r--r-- 1 Sascha None 9166 Sep 8 21:24 fixup_x.dat -rw-r--r-- 1 Sascha None 137 Sep 9 10:10 issue.txt -rw-r--r-- 1 Sascha None 72 Dec 24 11:02 kernel.img -rw-r--r-- 1 Sascha None 3232856 Sep 8 21:24 kernel.img.orig -rw-r--r-- 1 Sascha None 2615064 Sep 8 21:24 start.elf -rw-r--r-- 1 Sascha None 533080 Sep 8 21:24 start_cd.elf -rw-r--r-- 1 Sascha None 3572200 Sep 8 21:24 start_x.elf
But when I boot the modified SD card nothing starts blinking. And I have no idea why. I tried already kernel_old in config.txt but this does not have any effect and I do not think that this is necessary, because the listing shows that the code starts at 0x8000.
While comparing the listing with the hex dump of the kernel.img file I can see a difference in the endianness. The listing starts with e59f003c.
~/Downloads/ok02$ cat kernel.list
build/output.elf: file format elf32-littlearm
Disassembly of section .init:
00008000 :
8000: e59f003c ldr r0, [pc, #60] ; 8044
8004: e3a01001 mov r1, #1
8008: e1a01901 lsl r1, r1, #18
800c: e5801004 str r1, [r0, #4]
8010: e3a01001 mov r1, #1
8014: e1a01801 lsl r1, r1, #16
00008018 :
8018: e5801028 str r1, [r0, #40] ; 0x28
801c: e3a0283f mov r2, #4128768 ; 0x3f0000
00008020 :
8020: e2422001 sub r2, r2, #1
8024: e3520000 cmp r2, #0
8028: 1afffffc bne 8020
802c: e580101c str r1, [r0, #28]
8030: e3a0283f mov r2, #4128768 ; 0x3f0000
00008034 :
8034: e2422001 sub r2, r2, #1
8038: e3520000 cmp r2, #0
803c: 1afffffc bne 8034
8040: eafffff4 b 8018
8044: 20200000 .word 0x20200000
But the hex dump starts with 003ce59f.
~/Downloads/ok02$ hexdump -x kernel.img 0000000 003c e59f 1001 e3a0 1901 e1a0 1004 e580 0000010 1001 e3a0 1801 e1a0 1028 e580 283f e3a0 0000020 2001 e242 0000 e352 fffc 1aff 101c e580 0000030 283f e3a0 2001 e242 0000 e352 fffc 1aff 0000040 fff4 eaff 0000 2020 0000048
Is this correct or wrong?
And if it is correct, what else could be the reason why the code from lesson 2 does not work?
