Implement cooperative threads on hosted platforms using C code.

This replaces SDL threads with real cooperative threads, which are less cpu intensive and allow priority scheduling.
The backend for context switching is dependant on the host (sigaltstack/longjmp on Unix, Fibers on Windows).
configure has options to force or disallow SDL threads.

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@29327 a1c6a512-1295-4272-9138-f99709370657

1 files changed, 98 insertions, 0 deletions

diff --git a/firmware/target/hosted/thread-arm.c b/firmware/target/hosted/thread-arm.c
new file mode 100644
index 0000000000..d2fa7d1e5d
--- /dev/null
+++ b/firmware/target/hosted/thread-arm.c
@@ -0,0 +1,98 @@
+/***************************************************************************
+ *             __________               __   ___.
+ *   Open      \______   \ ____   ____ |  | _\_ |__   _______  ___
+ *   Source     |       _//  _ \_/ ___\|  |/ /| __ \ /  _ \  \/  /
+ *   Jukebox    |    |   (  <_> )  \___|    < | \_\ (  <_> > <  <
+ *   Firmware   |____|_  /\____/ \___  >__|_ \|___  /\____/__/\_ \
+ *                     \/            \/     \/    \/            \/
+ * $Id$
+ *
+ * Copyright (C) 2005 by Thom Johansen
+ * Copyright (C) 2010 by Thomas Martitz (Android-suitable core_sleep())
+ *
+ * Generic ARM threading support
+ *
+ * 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 <system.h>
+/*---------------------------------------------------------------------------
+ * Start the thread running and terminate it if it returns
+ *---------------------------------------------------------------------------
+ */
+static void __attribute__((naked,used)) start_thread(void)
+{
+    /* r0 = context */
+    asm volatile (
+        "ldr    sp, [r0, #32]            \n" /* Load initial sp */
+        "ldr    r4, [r0, #40]            \n" /* start in r4 since it's non-volatile */
+        "mov    r1, #0                   \n" /* Mark thread as running */
+        "str    r1, [r0, #40]            \n"
+        "mov    lr, pc                   \n" /* Call thread function */
+        "bx     r4                       \n"
+    ); /* No clobber list - new thread doesn't care */
+    thread_exit();
+}
+
+/* For startup, place context pointer in r4 slot, start_thread pointer in r5
+ * slot, and thread function pointer in context.start. See load_context for
+ * what happens when thread is initially going to run. */
+#define THREAD_STARTUP_INIT(core, thread, function) \
+    ({ (thread)->context.r[0] = (uint32_t)&(thread)->context,  \
+       (thread)->context.r[1] = (uint32_t)start_thread, \
+       (thread)->context.start = (uint32_t)function; })
+
+
+/*---------------------------------------------------------------------------
+ * Store non-volatile context.
+ *---------------------------------------------------------------------------
+ */
+static inline void store_context(void* addr)
+{
+    asm volatile(
+        "stmia  %0, { r4-r11, sp, lr } \n"
+        : : "r" (addr)
+    );
+}
+
+/*---------------------------------------------------------------------------
+ * Load non-volatile context.
+ *---------------------------------------------------------------------------
+ */
+static inline void load_context(const void* addr)
+{
+    asm volatile(
+        "ldr     r0, [%0, #40]          \n" /* Load start pointer */
+        "cmp     r0, #0                 \n" /* Check for NULL */
+
+        /* If not already running, jump to start */
+        "ldmneia %0, { r0, pc }         \n"
+        "ldmia   %0, { r4-r11, sp, lr } \n" /* Load regs r4 to r14 from context */
+        : : "r" (addr) : "r0" /* only! */
+    );
+}
+
+/*
+ * this core sleep suspends the OS thread rockbox runs under, which greatly
+ * reduces cpu usage (~100% to <10%)
+ *
+ * it returns when when the tick timer is called, other interrupt-like
+ * events occur
+ *
+ * wait_for_interrupt is implemented in kernel-<platform>.c
+ **/
+
+static inline void core_sleep(void)
+{
+    enable_irq();
+    wait_for_interrupt();
+}
+
+