By: David Merchant

David Merchant — Sat, 23 Dec 2017 04:20:22 +0000

Not sure where this question should go under what chapter. I would like to find a reference to implementing/ programming an I2C MEMS IMU, the BNO055. I can see it with I2Cdetect but for the life of me I can’t write a program that talks to it and gets data back. Any ideas? .thank you

By: admin

admin — Sun, 03 Jul 2016 12:45:32 +0000

Thanks Angelo, that should be platform-dependent assembler code. To illustrate this point further I have added the two .s file examples below, the first is compiled with a native compiler under x86 and the second is compiled using a cross-compiler to ARMHF. The .s files can be compared.
The .c source file:

molloyd@molloyd-VirtualBox:~/temp$ more test.c
#include
int main(){
   printf("Hello World\n");
   return 0;
}

molloyd@molloyd-VirtualBox:~/temp$ more test.c

#include

int main(){

printf("Hello World\n");

return 0;

}

The Intel x86 Code:

molloyd@molloyd-VirtualBox:~/temp$ gcc -S test.c
molloyd@molloyd-VirtualBox:~/temp$ more test.s
	.file	"test.c"
	.section	.rodata
.LC0:
	.string	"Hello World"
	.text
	.globl	main
	.type	main, @function
main:
.LFB0:
	.cfi_startproc
	pushq	%rbp
	.cfi_def_cfa_offset 16
	.cfi_offset 6, -16
	movq	%rsp, %rbp
	.cfi_def_cfa_register 6
	movl	$.LC0, %edi
	call	puts
	movl	$0, %eax
	popq	%rbp
	.cfi_def_cfa 7, 8
	ret
	.cfi_endproc
.LFE0:
	.size	main, .-main
	.ident	"GCC: (Ubuntu 5.3.1-14ubuntu2.1) 5.3.1 20160413"
	.section	.note.GNU-stack,"",@progbits

molloyd@molloyd-VirtualBox:~/temp$ gcc -S test.c

molloyd@molloyd-VirtualBox:~/temp$ more test.s

.file "test.c"

.section .rodata

.LC0:

.string "Hello World"

.text

.globl main

.type main, @function

main:

.LFB0:

.cfi_startproc

pushq %rbp

.cfi_def_cfa_offset 16

.cfi_offset 6, -16

movq %rsp, %rbp

.cfi_def_cfa_register 6

movl $.LC0, %edi

call puts

movl $0, %eax

popq %rbp

.cfi_def_cfa 7, 8

ret

.cfi_endproc

.LFE0:

.size main, .-main

.ident "GCC: (Ubuntu 5.3.1-14ubuntu2.1) 5.3.1 20160413"

.section .note.GNU-stack,"",@progbits

And the equivalent ARMHF code:

molloyd@molloyd-VirtualBox:~/temp$ arm-linux-gnueabihf-gcc -S test.c -o test1.s
molloyd@molloyd-VirtualBox:~/temp$ more test1.s
	.arch armv7-a
	.eabi_attribute 28, 1
	.fpu vfpv3-d16
	.eabi_attribute 20, 1
	.eabi_attribute 21, 1
	.eabi_attribute 23, 3
	.eabi_attribute 24, 1
	.eabi_attribute 25, 1
	.eabi_attribute 26, 2
	.eabi_attribute 30, 6
	.eabi_attribute 34, 1
	.eabi_attribute 18, 4
	.file	"test.c"
	.section	.rodata
	.align	2
.LC0:
	.ascii	"Hello World\000"
	.text
	.align	2
	.global	main
	.syntax unified
	.thumb
	.thumb_func
	.type	main, %function
main:
	@ args = 0, pretend = 0, frame = 0
	@ frame_needed = 1, uses_anonymous_args = 0
	push	{r7, lr}
	add	r7, sp, #0
	movw	r0, #:lower16:.LC0
	movt	r0, #:upper16:.LC0
	bl	puts
	movs	r3, #0
	mov	r0, r3
	pop	{r7, pc}
	.size	main, .-main
	.ident	"GCC: (Ubuntu/Linaro 5.3.1-14ubuntu2) 5.3.1 20160413"
	.section	.note.GNU-stack,"",%progbits

molloyd@molloyd-VirtualBox:~/temp$ arm-linux-gnueabihf-gcc -S test.c -o test1.s

molloyd@molloyd-VirtualBox:~/temp$ more test1.s

.arch armv7-a

.eabi_attribute 28, 1

.fpu vfpv3-d16

.eabi_attribute 20, 1

.eabi_attribute 21, 1

.eabi_attribute 23, 3

.eabi_attribute 24, 1

.eabi_attribute 25, 1

.eabi_attribute 26, 2

.eabi_attribute 30, 6

.eabi_attribute 34, 1

.eabi_attribute 18, 4

.file "test.c"

.section .rodata

.align 2

.LC0:

.ascii "Hello World\000"

.text

.align 2

.global main

.syntax unified

.thumb

.thumb_func

.type main, %function

main:

@ args = 0, pretend = 0, frame = 0

@ frame_needed = 1, uses_anonymous_args = 0

push {r7, lr}

add r7, sp, #0

movw r0, #:lower16:.LC0

movt r0, #:upper16:.LC0

bl puts

movs r3, #0

mov r0, r3

pop {r7, pc}

.size main, .-main

.ident "GCC: (Ubuntu/Linaro 5.3.1-14ubuntu2) 5.3.1 20160413"

.section .note.GNU-stack,"",%progbits

Each of the outputs are platform dependent. Thanks, Derek.

By: Angelo

Angelo — Sat, 02 Jul 2016 19:13:27 +0000

Erratum: Page 184 contains the phrase

“platform-independent assembler code”.

Assembler code is not platform independent. Maybe what you mean is that it is still a text file, not a binary?

The beablebone book contains the same error on page 171.

Comments on: Chapters

By: David Merchant

By: admin

By: Angelo