ARM assembly cannot use immediate values and ADDS/ADCS together

I am currently trying to speed up some of my C functions on a Cortex-M0 (Freescale KL25Z) using assembly. I get a problem with this minimal test program:

@.syntax unified
.cpu cortex-m0
.text
.global test
.code 16
test:
mov r0, #0
adds r0, r0, #1
bx lr


When I try to assemble my .s file to a .o file, I get this error

$ arm-none-eabi-as test.s -o test.o
test.s: Assembler messages:
test.s:8: Error: instruction not supported in Thumb16 mode -- `adds r0,r0,#1'

The error message doesn't make sense to me, ADDS is a valid instruction acording to [this document][1]. I found [a possible answer on stackoverflow][2] and added the line at the beginning of the program (".syntax unified" worked, like the second answer suggested). This resulted in fixing this problem, I can now use instructions like ADDS and ADCS, but I did get a new error:

$ arm-none-eabi-as test.s -o test.o
test.s: Assembler messages:
test.s:7: Error: cannot honor width suffix -- `mov r0,#0'

Some instructions using immediate values get this error. I am compiling on Mac OS 10.9.5. I can't find a solution to this via Google or Stackoverflow and have no idea how to get around these errors.

$ arm-none-eabi-gcc --version
arm-none-eabi-gcc (GNU Tools for ARM Embedded Processors) 4.9.3 20150303 (release) [ARM/embedded-4_9-branch revision 221220]
Copyright © 2014 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

$ arm-none-eabi-as --version
GNU assembler (GNU Tools for ARM Embedded Processors) 2.24.0.20150304
Copyright 2013 Free Software Foundation, Inc.
This program is free software; you may redistribute it under the terms of
the GNU General Public License version 3 or later.
This program has absolutely no warranty.
This assembler was configured for a target of `arm-none-eabi'.

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In thumb mode, you can not use `adds`, you only have `add`. As such, the correct code is:

.cpu cortex-m0
.text
.global test
.code 16
test:
mov r0, #0
add r0, r0, #1
bx lr

Somewhat ironically, by using UAL syntax to solve the first problem you've now hit pretty much the same thing, but the other way round and with a rather more cryptic symptom.

The only Thumb encodings for (non-flag-setting) `mov` with an immediate operand are 32-bit ones, however Cortex-M0 doesn't support those, so the assembler ends up choking on its own constraints. In UAL you have to explicitly use `movs` to get [the only "move immediate" instruction Cortex-M0 actually has][1].

[1]:http://infocenter.arm.com/help/topic/com.arm.doc.ddi0432c/CHDCICDF.html

what Jester said:

.cpu cortex-m0
.text
.thumb

.thumb_func
.global test
test:
mov r0, #0
add r0, r0, #1
bx lr


which gives

0: 2000 movs r0, #0
2: 3001 adds r0, #1
4: 4770 bx lr

or if you go with syntax unified then you have to put the s on there

.syntax unified
.cpu cortex-m0
.text
.thumb

.thumb_func
.global test
test:
movs r0, #0
adds r0, r0, #1
bx lr

which also gives


00000000 <test>:
0: 2000 movs r0, #0
2: 3001 adds r0, #1
4: 4770 bx lr