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basecmd: Improve accuracy of stats "sumsq" variable 

Use a base of 256 instead of 65536 when calculating the sum of the
square of the clock differences in the stats.  This makes the
calculation more accurate.  Export the new base via DECL_CONSTANT for
the host to access.  Use DIV_ROUND_UP() when adjusting for the base to
ensure no lost ticks.  Do the division after multiplication in the
common case where the time between stats_task() invocations is less
than 64K ticks.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
This commit is contained in:
Kevin O'Connor 2017-01-09 23:08:23 -05:00
parent c87c090264
commit 3a7a77d49e
2 changed files with 18 additions and 6 deletions
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9
klippy/mcu.py
View File

@ -333,6 +333,7 @@ class MCU:
self._print_start_time = 0.
self._mcu_freq = 0.
# Stats
self._stats_sumsq_base = 0.
self._mcu_tick_avg = 0.
self._mcu_tick_stddev = 0.
def handle_mcu_stats(self, params):
@ -341,10 +342,8 @@ class MCU:
tick_sum = params['sum']
c = 1.0 / (count * self._mcu_freq)
self._mcu_tick_avg = tick_sum * c
tick_sumsq = params['sumsq']
tick_sumavgsq = ((tick_sum // (256*count)) * count)**2
self._mcu_tick_stddev = c * 256. * math.sqrt(
count * tick_sumsq - tick_sumavgsq)
tick_sumsq = params['sumsq'] * self._stats_sumsq_base
self._mcu_tick_stddev = c * math.sqrt(count*tick_sumsq - tick_sum**2)
def handle_shutdown(self, params):
if self.is_shutdown:
return
@ -359,6 +358,8 @@ class MCU:
self._printer.reactor.update_timer(
self._timeout_timer, time.time() + self.COMM_TIMEOUT)
self._mcu_freq = float(self.serial.msgparser.config['CLOCK_FREQ'])
self._stats_sumsq_base = float(
self.serial.msgparser.config['STATS_SUMSQ_BASE'])
self._emergency_stop_cmd = self.lookup_command("emergency_stop")
self._clear_shutdown_cmd = self.lookup_command("clear_shutdown")
self.register_msg(self.handle_shutdown, 'shutdown')

15
src/basecmd.c
View File

@ -191,15 +191,26 @@ command_get_status(uint32_t *args)
}
DECL_COMMAND_FLAGS(command_get_status, HF_IN_SHUTDOWN, "get_status");
#define SUMSQ_BASE 256
DECL_CONSTANT(STATS_SUMSQ_BASE, SUMSQ_BASE);
static void
stats_task(void)
{
static uint32_t last, count, sumsq;
uint32_t cur = sched_read_time();
uint32_t diff = (cur - last) >> 8;
uint32_t diff = cur - last;
last = cur;
count++;
uint32_t nextsumsq = sumsq + diff*diff;
// Calculate sum of diff^2 - be careful of integer overflow
uint32_t nextsumsq;
if (diff <= 0xffff) {
nextsumsq = sumsq + DIV_ROUND_UP(diff * diff, SUMSQ_BASE);
} else if (diff <= 0xfffff) {
nextsumsq = sumsq + DIV_ROUND_UP(diff, SUMSQ_BASE) * diff;
} else {
nextsumsq = 0xffffffff;
}
if (nextsumsq < sumsq)
nextsumsq = 0xffffffff;
sumsq = nextsumsq;