From 3ec66893e377b088c1284d2d23adb2aeea6d7965 Mon Sep 17 00:00:00 2001
From: Aidan MacDonald <amachronic@protonmail.com>
Date: Sat, 27 Feb 2021 22:08:58 +0000
Subject: New port: FiiO M3K on bare metal

Change-Id: I7517e7d5459e129dcfc9465c6fbd708619888fbe
---
 firmware/target/mips/ingenic_x1000/kernel-x1000.c | 74 +++++++++++++++++++++++
 1 file changed, 74 insertions(+)
 create mode 100644 firmware/target/mips/ingenic_x1000/kernel-x1000.c

(limited to 'firmware/target/mips/ingenic_x1000/kernel-x1000.c')

diff --git a/firmware/target/mips/ingenic_x1000/kernel-x1000.c b/firmware/target/mips/ingenic_x1000/kernel-x1000.c
new file mode 100644
index 0000000000..c8105a3446
--- /dev/null
+++ b/firmware/target/mips/ingenic_x1000/kernel-x1000.c
@@ -0,0 +1,74 @@
+/***************************************************************************
+ *             __________               __   ___.
+ *   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)
+{
+    /* 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;
+    }
+
+    /* Call regular kernel tick */
+    jz_write(OST_1FLG, 0);
+    call_tick_tasks();
+}
-- 
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