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>

diff --git a/target/xtensa/core-dc232b.c b/target/xtensa/core-dc232b.c
index aa07018af4e70403e0f5fee09fba533ad8e40b52..7331eeea2fb6f0e5056ad77c43d2e49d253f11bc 100644 (file)
--- 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 2882c431e4a9814704c97da46b0db536cfaf913f..091518c0558324e3a8e9872c6ea424aac3cb221f 100644 (file)
--- 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