[U-Boot] [PATCH v3 1/2] arm: add support for semihosting for ARMv7M targets

[Albert ARIBAUD <albert.u.boot@aribaud.net>]

Hello Vadzim,

On Mon, 19 Oct 2015 19:40:14 +0300, Vadzim Dambrouski <pftbest@gmail.com> wrote:
> If you enable CONFIG_SEMIHOSTING for STM32F429 target, you will get compile
> error looking like this:
> 
> arch/arm/lib/semihosting.c: In function 'smh_read':
> {standard input}: Assembler messages:
> {standard input}:34: Error: invalid swi expression
> {standard input}:34: Error: value of 1193046 too large for field of 2 bytes at 0
> scripts/Makefile.build:277: recipe for target 'arch/arm/lib/semihosting.o' failed
> 
> The source of the problem is "svc #0x123456" instruction. This instruction
> can not be encoded using Thumb2 instruction set used by ARMv7M CPUs.
> ARM documentation suggests using "bkpt #0xAB" instruction instead [1].
> This patch fixes compile errors and adds support for semihosting for
> STM32F429 or any other ARMv7M target.
> This change was sested on STM32F429-DISCOVERY board using OpenOCD and
> "smhload" u-boot command.
> 
> [1] http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0471c/Bgbjhiea.html
> 
> Signed-off-by: Vadzim Dambrouski <pftbest@gmail.com>
> ---
> 
>  arch/arm/lib/semihosting.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/arch/arm/lib/semihosting.c b/arch/arm/lib/semihosting.c
> index c3e964e..ed5e8e4 100644
> --- a/arch/arm/lib/semihosting.c
> +++ b/arch/arm/lib/semihosting.c
> @@ -31,6 +31,8 @@ static noinline long smh_trap(unsigned int sysnum, void *addr)
>  	register long result asm("r0");
>  #if defined(CONFIG_ARM64)
>  	asm volatile ("hlt #0xf000" : "=r" (result) : "0"(sysnum), "r"(addr));
> +#elif defined(CONFIG_CPU_V7M)
> +	asm volatile ("bkpt #0xAB" : "=r" (result) : "0"(sysnum), "r"(addr));
>  #else
>  	/* Note - untested placeholder */
>  	asm volatile ("svc #0x123456" : "=r" (result) : "0"(sysnum), "r"(addr));
> -- 
> 2.6.1
> 

Applied to u-boot-arm/master, thanks!

Amicalement,
-- 
Albert.