ldr r0,=0x20200000
Shouldn't the LDR be a MOV?
(http://www.woodmann.com/fravia/The%20ARM%20Processor.htm)
> The ARM assembler also supports a similar pseudo operation. The construct LDR rd,=value is used to load value into register rd. The LDR pseudo instruction uses the MOV or MOV instructions, or it places the constant in memory and uses program counter relative addressing to load the constant.
(http://sourceware.org/binutils/docs/as/ARM-Opcodes.html)
> If expression evaluates to a numeric constant then a MOV or MVN instruction will be used in place of the LDR instruction, if the constant can be generated by either of these instructions. Otherwise the constant will be placed into the nearest literal pool (if it not already there) and a PC relative LDR instruction will be generated.
Example, using a simple input:
.globl _start
_start:
ldr r0, =0x20200000
.globl _start
_start:
ldr r0, [pc, #-4]
.word 0x20200000The immediate pseudo-instruction:
http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc....
The regular form:
http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc....
However, I wonder if it isn't too painful in the long run to teach OS programming on a target where you have to flip SD cards every time you compile (as opposed to one of those with a hardware debugger included, like Launchpad or ST Discovery).
When I took Operating Systems (INF242 at Oslo) ten years ago, we wrote an operating system for PCs that booted from floppies, and debugging was largely a matter of poking bytes to 0xB800:0000, which made this course somewhat unpopular with students with little low-level programming experience.