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/***************************************************************************
* __________ __ ___.
* Open \______ \ ____ ____ | | _\_ |__ _______ ___
* Source | _// _ \_/ ___\| |/ /| __ \ / _ \ \/ /
* Jukebox | | ( <_> ) \___| < | \_\ ( <_> > < <
* Firmware |____|_ /\____/ \___ >__|_ \|___ /\____/__/\_ \
* \/ \/ \/ \/ \/
* $Id$
*
* Copyright (C) 2021 Aidan MacDonald
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version 2
* of the License, or (at your option) any later version.
*
* This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
* KIND, either express or implied.
*
****************************************************************************/
#include "kernel.h"
#include "system.h"
#include "x1000/ost.h"
/* TODO: implement a CPU frequency switching policy based on CPU utilization
*
* The basic assumption is that the workload consumes a fixed number of CPU
* cycles per second on average (= utilization), so we can set the frequency
* based on that value. Audio playback should fit this usage pattern well, so
* it's a good fit for Rockbox.
*
* It's easier to understand in terms of fluid flow -- we need to keep
* a reservoir of water topped up, CPU frequency is the inflow rate, and
* CPU utilization is the outflow rate. The goal is to avoid running dry
* and minimize the inflow rate.
*
* The only tricky part here is handing usage spikes -- CPU frequency has to
* increase faster than utilization or there's a risk of audio dropouts.
*
* Rockbox CPU boost could be used as a hint to scale up frequency faster.
* If that's not necessary to get good results, HAVE_ADJUSTABLE_CPU_FREQ can
* be disabled entirely.
*/
#define CPU_IDLE_SAMPLES 100
void tick_start(unsigned interval_in_ms)
{
jz_writef(OST_CTRL, PRESCALE1_V(BY_16));
jz_write(OST_1DFR, interval_in_ms*(X1000_EXCLK_FREQ/16000));
jz_write(OST_1CNT, 0);
jz_write(OST_1FLG, 0);
jz_write(OST_1MSK, 0);
jz_setf(OST_ENABLE, OST1);
}
void OST(void)
{
#ifdef X1000_CPUIDLE_STATS
/* CPU idle time accounting */
uint32_t now = __ost_read32();
uint32_t div = now - __cpu_idle_reftick;
if(div != 0) {
uint32_t fraction = 1000 * __cpu_idle_ticks / div;
__cpu_idle_avg += fraction - __cpu_idle_avg / CPU_IDLE_SAMPLES;
__cpu_idle_cur = __cpu_idle_avg / CPU_IDLE_SAMPLES;
__cpu_idle_ticks = 0;
__cpu_idle_reftick = now;
}
#endif
/* Call regular kernel tick */
jz_write(OST_1FLG, 0);
call_tick_tasks();
}
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