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