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target/xtensa: fix timers test 

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 <Pavel.Dovgaluk@ispras.ru>
Cc: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
master
Max Filippov 2018-03-23 05:56:19 -07:00
parent 12ab0b33f1
commit d0ce7e9cfc
2 changed files with 2 additions and 2 deletions
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2
target/xtensa/core-dc232b.c
View File

@ -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
};

2
tests/tcg/xtensa/Makefile
View File

@ -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