Re: [Qemu-devel] [PATCH v2] target/xtensa: fix timers test

[Philippe Mathieu-Daudé]

On 03/26/2018 02:56 PM, Max Filippov wrote:
> The value of CCOUNT special register is calculated as time elapsed
> since CCOUNT == 0 multiplied by the core frequency. In icount mode time
> increment between consecutive instructions that don't involve time
> warps is constant, but unless the result of multiplication of this
> constant by the core frequency is a whole number the CCOUNT increment
> between these instructions may not be constant. E.g. with icount=7 each
> instruction takes 128ns, with core clock of 10MHz CCOUNT values for
> consecutive instructions are:
> 
>   502: (128 * 502 * 10000000) / 1000000000 = 642.56
>   503: (128 * 503 * 10000000) / 1000000000 = 643.84
>   504: (128 * 504 * 10000000) / 1000000000 = 645.12
> 
> I.e.the CCOUNT increments depend on the absolute time. This results in
> varying CCOUNT differences for consecutive instructions in tests that
> involve time warps and don't set CCOUNT explicitly.
> 
> Change frequency of the core used in tests so that clock cycle takes
> exactly 64ns. Change icount power used in tests to 6, so that each
> instruction takes exactly 1 clock cycle. With these changes CCOUNT
> increments only depend on the number of executed instructions and that's
> what timer tests expect, so they work correctly.
> 
> Longer story:
>   http://lists.nongnu.org/archive/html/qemu-devel/2018-03/msg04326.html
> 
> Cc: Pavel Dovgaluk <address@hidden>
> Cc: Philippe Mathieu-Daudé <address@hidden>
> Signed-off-by: Max Filippov <address@hidden>

Reviewed-by: Philippe Mathieu-Daudé <address@hidden>

> ---
> Changes v1->v2:
> - expand changelog;
> - replace clock_freq_khz initializer constant with a more meaningful
>   expression.

Thanks :)

> 
>  target/xtensa/core-dc232b.c | 2 +-
>  tests/tcg/xtensa/Makefile   | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/target/xtensa/core-dc232b.c b/target/xtensa/core-dc232b.c
> index aa07018af4e7..7331eeea2fb6 100644
> --- a/target/xtensa/core-dc232b.c
> +++ b/target/xtensa/core-dc232b.c
> @@ -47,7 +47,7 @@ static XtensaConfig dc232b __attribute__((unused)) = {
>          }
>      },
>      .isa_internal = &xtensa_modules,
> -    .clock_freq_khz = 10000,
> +    .clock_freq_khz = (NANOSECONDS_PER_SECOND / 64) / 1000,
>      DEFAULT_SECTIONS
>  };
>  
> diff --git a/tests/tcg/xtensa/Makefile b/tests/tcg/xtensa/Makefile
> index 2882c431e4a9..091518c05583 100644
> --- a/tests/tcg/xtensa/Makefile
> +++ b/tests/tcg/xtensa/Makefile
> @@ -5,7 +5,7 @@ CROSS=xtensa-$(CORE)-elf-
>  
>  ifndef XT
>  SIM = ../../../xtensa-softmmu/qemu-system-xtensa
> -SIMFLAGS = -M sim -cpu $(CORE) -nographic -semihosting -icount 7 $(EXTFLAGS) 
> -kernel
> +SIMFLAGS = -M sim -cpu $(CORE) -nographic -semihosting -icount 6 $(EXTFLAGS) 
> -kernel
>  SIMDEBUG = -s -S
>  else
>  SIM = xt-run
>