mkimxboot: rewrite dualboot

Rewrite dualboot in C code instead of assembly. Also properly
handle subtarget and simply Makefile. This should make the
dualboot stub more readable and easier to extend. The new code
also gracefully handles power up from RTC alarm on imx233.

Change-Id: I7c225254b1463a97e76b6cb4de476aa2d2c9d2f9

6 files changed, 222 insertions, 161 deletions

diff --git a/rbutil/mkimxboot/dualboot.c b/rbutil/mkimxboot/dualboot.c
index 20876d77b0..6f8f5c423d 100644
--- a/rbutil/mkimxboot/dualboot.c
+++ b/rbutil/mkimxboot/dualboot.c
@@ -2,28 +2,34 @@
 
 #include "dualboot.h"
 
-unsigned char dualboot_fuzeplus[152] = {
-    0x78, 0x20, 0x9f, 0xe5, 0x00, 0x20, 0x92, 0xe5, 0x01, 0x01, 0x12, 0xe3, 0x00, 0x00, 0xa0, 0x03,
-    0x1e, 0xff, 0x2f, 0x01, 0x70, 0x40, 0x2d, 0xe9, 0x64, 0x20, 0x9f, 0xe5, 0x00, 0x20, 0x92, 0xe5,
-    0x02, 0x21, 0xa0, 0xe1, 0x22, 0x2d, 0xa0, 0xe1, 0x20, 0x00, 0x12, 0xe3, 0x0c, 0x00, 0x00, 0x1a,
-    0x50, 0x20, 0x9f, 0xe5, 0x00, 0x40, 0xa0, 0xe3, 0x44, 0x30, 0x9f, 0xe5, 0x00, 0x30, 0x93, 0xe5,
-    0x03, 0x35, 0xa0, 0xe1, 0x23, 0x3f, 0xa0, 0xe1, 0x01, 0x00, 0x53, 0xe3, 0x03, 0x40, 0x84, 0x00,
-    0x01, 0x20, 0x52, 0xe2, 0xf7, 0xff, 0xff, 0x1a, 0x2c, 0x20, 0x9f, 0xe5, 0x02, 0x00, 0x54, 0xe1,
-    0x02, 0x00, 0x00, 0x3a, 0x00, 0x00, 0x81, 0xe5, 0x01, 0x00, 0xa0, 0xe3, 0x70, 0x80, 0xbd, 0xe8,
-    0x18, 0x00, 0x9f, 0xe5, 0x18, 0x10, 0x9f, 0xe5, 0x00, 0x10, 0x80, 0xe5, 0xfb, 0xff, 0xff, 0xea,
-    0x10, 0x86, 0x01, 0x80, 0xc0, 0x40, 0x04, 0x80, 0x70, 0x64, 0x08, 0x00, 0x80, 0x1a, 0x06, 0x00,
-    0x00, 0x41, 0x04, 0x80, 0x01, 0x00, 0x77, 0x3e
+unsigned char dualboot_fuzeplus[228] = {
+    0x10, 0x40, 0x2d, 0xe9, 0x00, 0x00, 0x00, 0xeb, 0x10, 0x80, 0xbd, 0xe8, 0x30, 0x00, 0x2d, 0xe9,
+    0x01, 0x50, 0xa0, 0xe1, 0xb4, 0x30, 0x9f, 0xe5, 0xc0, 0x30, 0x93, 0xe5, 0x3f, 0x34, 0x03, 0xe2,
+    0x23, 0x3c, 0xa0, 0xe1, 0x20, 0x00, 0x13, 0xe3, 0x01, 0x30, 0xa0, 0x13, 0x02, 0x00, 0x00, 0x1a,
+    0x10, 0x00, 0x13, 0xe3, 0x02, 0x30, 0xa0, 0x13, 0x00, 0x30, 0xa0, 0x03, 0x90, 0x20, 0x9f, 0xe5,
+    0x10, 0x26, 0x92, 0xe5, 0x01, 0x01, 0x12, 0xe3, 0x10, 0x00, 0x00, 0x0a, 0x00, 0x00, 0x53, 0xe3,
+    0x11, 0x00, 0x00, 0x1a, 0x03, 0x40, 0xa0, 0xe1, 0x70, 0x10, 0x9f, 0xe5, 0x74, 0xc0, 0x9f, 0xe5,
+    0xc0, 0x20, 0x91, 0xe5, 0x03, 0x26, 0x02, 0xe2, 0x01, 0x06, 0x52, 0xe3, 0x01, 0x40, 0x84, 0x02,
+    0x01, 0x30, 0x83, 0xe2, 0x0c, 0x00, 0x53, 0xe1, 0xf8, 0xff, 0xff, 0x1a, 0x58, 0x30, 0x9f, 0xe5,
+    0x03, 0x00, 0x54, 0xe1, 0x04, 0x00, 0x00, 0xca, 0x06, 0x00, 0x00, 0xea, 0xfe, 0xff, 0xff, 0xea,
+    0x00, 0x00, 0xa0, 0xe3, 0x30, 0x00, 0xbd, 0xe8, 0x1e, 0xff, 0x2f, 0xe1, 0x00, 0x00, 0x85, 0xe5,
+    0x01, 0x00, 0xa0, 0xe3, 0xfa, 0xff, 0xff, 0xea, 0x24, 0x30, 0x9f, 0xe5, 0x03, 0x27, 0xa0, 0xe3,
+    0x04, 0x21, 0x83, 0xe5, 0x02, 0x2c, 0xa0, 0xe3, 0x00, 0x27, 0x83, 0xe5, 0x00, 0x25, 0x83, 0xe5,
+    0x18, 0x20, 0x9f, 0xe5, 0x0b, 0x39, 0x83, 0xe2, 0x00, 0x21, 0x83, 0xe5, 0xee, 0xff, 0xff, 0xea,
+    0x00, 0x40, 0x04, 0x80, 0x00, 0x80, 0x01, 0x80, 0x70, 0x64, 0x08, 0x00, 0x7f, 0x1a, 0x06, 0x00,
+    0x01, 0x00, 0xff, 0xff
 };
-unsigned char dualboot_zenxfi2[92] = {
-    0x4c, 0x20, 0x9f, 0xe5, 0x00, 0x20, 0x92, 0xe5, 0x02, 0x21, 0xa0, 0xe1, 0x22, 0x2d, 0xa0, 0xe1,
-    0x20, 0x00, 0x12, 0xe3, 0x06, 0x00, 0x00, 0x0a, 0x34, 0x20, 0x9f, 0xe5, 0x00, 0x20, 0x92, 0xe5,
-    0x02, 0x25, 0xa0, 0xe1, 0x22, 0x2f, 0xa0, 0xe1, 0x01, 0x00, 0x52, 0xe3, 0x00, 0x00, 0xa0, 0x03,
-    0x03, 0x00, 0x00, 0xea, 0x1c, 0x20, 0x9f, 0xe5, 0x00, 0x20, 0x92, 0xe5, 0x01, 0x09, 0x12, 0xe3,
-    0x00, 0x00, 0xa0, 0x03, 0x1e, 0xff, 0x2f, 0x01, 0x00, 0x00, 0x81, 0xe5, 0x01, 0x00, 0xa0, 0xe3,
-    0x1e, 0xff, 0x2f, 0xe1, 0xc0, 0x40, 0x04, 0x80, 0x00, 0x86, 0x01, 0x80
+unsigned char dualboot_zenxfi2[96] = {
+    0x10, 0x40, 0x2d, 0xe9, 0x00, 0x00, 0x00, 0xeb, 0x10, 0x80, 0xbd, 0xe8, 0x44, 0x30, 0x9f, 0xe5,
+    0xc0, 0x30, 0x93, 0xe5, 0x02, 0x02, 0x13, 0xe3, 0x04, 0x00, 0x00, 0x1a, 0x38, 0x30, 0x9f, 0xe5,
+    0x00, 0x36, 0x93, 0xe5, 0x01, 0x09, 0x13, 0xe3, 0x08, 0x00, 0x00, 0x0a, 0x04, 0x00, 0x00, 0xea,
+    0x20, 0x30, 0x9f, 0xe5, 0xc0, 0x30, 0x93, 0xe5, 0x03, 0x36, 0x03, 0xe2, 0x01, 0x06, 0x53, 0xe3,
+    0x02, 0x00, 0x00, 0x0a, 0x00, 0x00, 0x81, 0xe5, 0x01, 0x00, 0xa0, 0xe3, 0x1e, 0xff, 0x2f, 0xe1,
+    0x00, 0x00, 0xa0, 0xe3, 0x1e, 0xff, 0x2f, 0xe1, 0x00, 0x40, 0x04, 0x80, 0x00, 0x80, 0x01, 0x80
 };
-unsigned char dualboot_zenxfi3[36] = {
-    0x18, 0x20, 0x9f, 0xe5, 0x00, 0x20, 0x92, 0xe5, 0x80, 0x00, 0x12, 0xe3, 0x00, 0x00, 0xa0, 0x03,
-    0x1e, 0xff, 0x2f, 0x01, 0x00, 0x00, 0x81, 0xe5, 0x01, 0x00, 0xa0, 0xe3, 0x1e, 0xff, 0x2f, 0xe1,
-    0x20, 0x86, 0x01, 0x80
+unsigned char dualboot_zenxfi3[56] = {
+    0x10, 0x40, 0x2d, 0xe9, 0x00, 0x00, 0x00, 0xeb, 0x10, 0x80, 0xbd, 0xe8, 0x1c, 0x30, 0x9f, 0xe5,
+    0xc0, 0x30, 0x93, 0xe5, 0x18, 0x30, 0x9f, 0xe5, 0x20, 0x36, 0x93, 0xe5, 0x80, 0x00, 0x13, 0xe3,
+    0x00, 0x00, 0xa0, 0x03, 0x00, 0x00, 0x81, 0x15, 0x01, 0x00, 0xa0, 0x13, 0x1e, 0xff, 0x2f, 0xe1,
+    0x00, 0x40, 0x04, 0x80, 0x00, 0x80, 0x01, 0x80
 };
diff --git a/rbutil/mkimxboot/dualboot.h b/rbutil/mkimxboot/dualboot.h
index eff50cc6c5..8ebde559f5 100644
--- a/rbutil/mkimxboot/dualboot.h
+++ b/rbutil/mkimxboot/dualboot.h
@@ -1,5 +1,5 @@
 /* Generated by bin2c */
 
-extern unsigned char dualboot_fuzeplus[152];
-extern unsigned char dualboot_zenxfi2[92];
-extern unsigned char dualboot_zenxfi3[36];
+extern unsigned char dualboot_fuzeplus[228];
+extern unsigned char dualboot_zenxfi2[96];
+extern unsigned char dualboot_zenxfi3[56];
diff --git a/rbutil/mkimxboot/dualboot/Makefile b/rbutil/mkimxboot/dualboot/Makefile
index 6386b7c622..4bad3a4a12 100644
--- a/rbutil/mkimxboot/dualboot/Makefile
+++ b/rbutil/mkimxboot/dualboot/Makefile
@@ -1,33 +1,38 @@
 CC=gcc
-CROSS_PREFIX=arm-elf-eabi
-# Edit the following variables (plus copy/paste another set of rules) when
-# adding a new target.  mkimxboot.c also needs to be edited to refer to these
-# new images.
-
-BOOTOBJS = dualboot_fuzeplus.o dualboot_zenxfi2.o dualboot_zenxfi3.o
-BOOTBINS = dualboot_fuzeplus.arm-bin dualboot_zenxfi2.arm-bin dualboot_zenxfi3.arm-bin
+LD=ld
+OC=objcopy
+CROSS_PREFIX=arm-elf-eabi-
+REGS_PATH=../../../firmware/target/arm/imx233/regs
+CFLAGS=-mcpu=arm926ej-s -std=gnu99 -I. -I$(REGS_PATH) -nostdlib -ffreestanding -fomit-frame-pointer -O
+# Edit the following variables when adding a new target.
+# mkimxboot.c also needs to be edited to refer to these
+# To add a new target x you need to:
+# 1) add x to the list in TARGETS
+# 2) create a variable named OPT_x of the form:
+#    OPT_x=target specific defines
+TARGETS=fuzeplus zenxfi2 zenxfi3
+OPT_fuzeplus=-DSANSA_FUZEPLUS -DIMX233_SUBTARGET=3780
+OPT_zenxfi2=-DCREATIVE_ZENXFI2 -DIMX233_SUBTARGET=3780
+OPT_zenxfi3=-DCREATIVE_ZENXFI3 -DIMX233_SUBTARGET=3780
+
+BOOTOBJS=$(patsubst %, dualboot_%.o, $(TARGETS))
+BOOTBINS=$(patsubst %, dualboot_%.arm-bin, $(TARGETS))
 
 all: ../dualboot.h ../dualboot.c
 
 # Dualboot bootloaders
 
-dualboot_fuzeplus.o: dualboot.S
-        $(CROSS_PREFIX)-$(CC) -mcpu=arm926ej-s -DSANSA_FUZEPLUS -c -o dualboot_fuzeplus.o dualboot.S
-
-dualboot_zenxfi2.o: dualboot.S
-        $(CROSS_PREFIX)-$(CC) -mcpu=arm926ej-s -DCREATIVE_ZENXFI2 -c -o dualboot_zenxfi2.o dualboot.S
+dualboot_%.o: dualboot.c
+        $(CROSS_PREFIX)$(CC) $(CFLAGS) $(OPT_$(@:dualboot_%.o=%)) -c -o $@ $^
 
-dualboot_zenxfi3.o: dualboot.S
-        $(CROSS_PREFIX)-$(CC) -mcpu=arm926ej-s -DCREATIVE_ZENXFI3 -c -o dualboot_zenxfi3.o dualboot.S
+dualboot_%.arm-elf: dualboot_%.o
+        $(CROSS_PREFIX)$(LD) $(LDFLAGS) -Tdualboot.lds -o $@ $<
 
 # Rules for the ARM code embedded in mkamsboot - assemble, link, then extract
 # the binary code and finally convert to .h for building in mkamsboot
 
-%.arm-elf: %.o
-        $(CROSS_PREFIX)-ld -Tdualboot.lds -o $@ $<
-
 %.arm-bin: %.arm-elf
-        $(CROSS_PREFIX)-objcopy -O binary $< $@
+        $(CROSS_PREFIX)$(OC) -O binary $< $@
 
 ../dualboot.c ../dualboot.h: $(BOOTBINS) bin2c
         ./bin2c ../dualboot $(BOOTBINS)
diff --git a/rbutil/mkimxboot/dualboot/dualboot.S b/rbutil/mkimxboot/dualboot/dualboot.S
deleted file mode 100644
index 0508f7e16a..0000000000
--- a/rbutil/mkimxboot/dualboot/dualboot.S
+++ /dev/null
@@ -1,118 +0,0 @@
-/***************************************************************************
- *             __________               __   ___.
- *   Open      \______   \ ____   ____ |  | _\_ |__   _______  ___
- *   Source     |       _//  _ \_/ ___\|  |/ /| __ \ /  _ \  \/  /
- *   Jukebox    |    |   (  <_> )  \___|    < | \_\ (  <_> > <  <
- *   Firmware   |____|_  /\____/ \___  >__|_ \|___  /\____/__/\_ \
- *                     \/            \/     \/    \/            \/
- * $Id$
- *
- * Copyright (C) 2011 by Amaury Pouly
- *
- * 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.
- *
- ****************************************************************************/
-
-.text
-.global start
-@ int start(uint32_t arg, uint32_t *result_id)
-start:
-#if defined(SANSA_FUZEPLUS)
-    /* If volume down key is hold, return so that the OF can boot */
-    ldr     r2, =0x80018610 @ HW_PINCTRL_DIN1
-    ldr     r2, [r2]
-    tst     r2, #0x40000000 @ bit 30, active low
-    moveq   r0, #0 @ return 0, continue boot
-    bxeq    lr
-    /* save registers for the ROM */
-    stmfd   sp!, {r4-r6,lr}
-    /* if the power source was 5v (ie usb), bypass the power button delay */
-    ldr     r2, =0x800440c0 @ HW_POWER_STS
-    ldr     r2, [r2]
-    mov     r2, r2, lsl#2
-    mov     r2, r2, lsr#26 @ extract PWRUP_SOURCE
-    tst     r2, #0x20 @ bit 5: five volts
-    bne     boot_rockbox
-    /* otherwise monitor the power button for a short time */
-    ldr     r2, =550000 @ loop count
-    ldr     r4, =0 @ number of times PSWITCH was 1
-pswitch_monitor_loop:
-    ldr     r3, =0x800440c0 @ HW_POWER_STS
-    ldr     r3, [r3]
-    mov     r3, r3, lsl#10
-    mov     r3, r3, lsr#30 @ extract PSWITCH
-    cmp     r3, #1
-    addeq   r4, r3 @ add one if PSWITCH=1 (means power hold)
-    subs    r2, #1
-    bne     pswitch_monitor_loop
-    /* power down if power wasn't hold long enough */
-    ldr     r2, =400000
-    cmp     r4, r2
-    bcc     power_down
-    /* jump to section given as argument */
-boot_rockbox:
-    str     r0, [r1]
-    mov     r0, #1
-    ldmfd   sp!, {r4-r6,pc}
-power_down:
-    ldr     r0, =0x80044100 @ HW_POWER_RESET
-    ldr     r1, =0x3E770001 @ unlock key + power down
-    str     r1, [r0]
-    b       power_down
-#elif defined(CREATIVE_ZENXFI2)
-    /* We are lacking buttons on the Zen X-Fi2 because on USB, the select button
-     * enters recovery mode ! So we can only use power but power is used to power up
-     * on normal boots and then select is free ! Thus use a non-uniform scheme:
-     * - normal boot:
-     *   - no key: Rockbox
-     *   - select: OF
-     * - USB boot:
-     *   - no key: Rockbox
-     *   - power: OF
-     */
-    /* if the power source was 5v (ie usb), check for power (pswitch) */
-    ldr     r2, =0x800440c0 @ HW_POWER_STS
-    ldr     r2, [r2]
-    mov     r2, r2, lsl#2
-    mov     r2, r2, lsr#26 @ extract PWRUP_SOURCE
-    tst     r2, #0x20 @ bit 5: five volts
-    beq     boot_normal
-    /* check pswitch*/
-    ldr     r2, =0x800440c0 @ HW_POWER_STS
-    ldr     r2, [r2]
-    mov     r2, r2, lsl#10
-    mov     r2, r2, lsr#30 @ extract PSWITCH
-    cmp     r2, #1
-    moveq   r0, #0 @ 1 => boot OF
-    b       do_boot
-boot_normal:
-    /* If select key is hold, return so that the OF can boot */
-    ldr     r2, =0x80018600 @ HW_PINCTRL_DIN0
-    ldr     r2, [r2]
-    tst     r2, #0x4000 @ bit 14, active low
-    moveq   r0, #0 @ return 0, continue boot
-    /* r0 must contain the 0 to boot OF and 1 to boot RB */
-do_boot:
-    bxeq    lr
-    str     r0, [r1]
-    mov     r0, #1
-    bx      lr
-#elif defined(CREATIVE_ZENXFI3)
-    /* If volume down key is hold, return so that the OF can boot */
-    ldr     r2, =0x80018620 @ HW_PINCTRL_DIN2
-    ldr     r2, [r2]
-    tst     r2, #0x80 @ bit 7, active low
-    moveq   r0, #0 @ return 0, continue boot
-    bxeq    lr
-    str     r0, [r1]
-    mov     r0, #1
-    bx      lr
-#else
-#error No target defined !
-#endif
diff --git a/rbutil/mkimxboot/dualboot/dualboot.c b/rbutil/mkimxboot/dualboot/dualboot.c
new file mode 100644
index 0000000000..301eca87ad
--- /dev/null
+++ b/rbutil/mkimxboot/dualboot/dualboot.c
@@ -0,0 +1,167 @@
+/***************************************************************************
+ *             __________               __   ___.
+ *   Open      \______   \ ____   ____ |  | _\_ |__   _______  ___
+ *   Source     |       _//  _ \_/ ___\|  |/ /| __ \ /  _ \  \/  /
+ *   Jukebox    |    |   (  <_> )  \___|    < | \_\ (  <_> > <  <
+ *   Firmware   |____|_  /\____/ \___  >__|_ \|___  /\____/__/\_ \
+ *                     \/            \/     \/    \/            \/
+ * $Id$
+ *
+ * Copyright (C) 2013 by Amaury Pouly
+ *
+ * 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 "regs-pinctrl.h"
+#include "regs-power.h"
+
+#define BOOT_ROM_CONTINUE   0 /* continue boot */
+#define BOOT_ROM_SECTION    1 /* switch to new section *result_id */
+
+typedef unsigned long uint32_t;
+
+// target specific boot context
+enum context_t
+{
+    CONTEXT_NORMAL, /* normal boot */
+    CONTEXT_USB, /* USB plugged boot */
+    CONTEXT_RTC, /* RTC wake up boot */
+};
+// target specific boot decision
+enum boot_t
+{
+    BOOT_STOP,  /* power down */
+    BOOT_ROCK, /* boot to Rockbox */
+    BOOT_OF, /* boot to OF */
+};
+
+/**
+ * Helper functions
+ */
+
+static inline int __attribute__((always_inline)) read_gpio(int bank, int pin)
+{
+    return (HW_PINCTRL_DINn(bank) >> pin) & 1;
+}
+
+static inline int __attribute__((always_inline)) read_pswitch(void)
+{
+#if IMX233_SUBTARGET >= 3700
+    return BF_RD(POWER_STS, PSWITCH);
+#else
+    return BF_RD(DIGCTL_STATUS, PSWITCH);
+#endif
+}
+
+static inline void __attribute__((noreturn)) power_down()
+{
+#ifdef SANSA_FUZEPLUS
+    /* B0P09: this pin seems to be important to shutdown the hardware properly */
+    HW_PINCTRL_MUXSELn_SET(0) = 3 << 18;
+    HW_PINCTRL_DOEn(0) = 1 << 9;
+    HW_PINCTRL_DOUTn(0) = 1 << 9;
+#endif
+    /* power down */
+    HW_POWER_RESET = BM_OR2(POWER_RESET, UNLOCK, PWD);
+    while(1);
+}
+
+/**
+ * Boot decision functions
+ */
+
+#if defined(SANSA_FUZEPLUS)
+static enum boot_t boot_decision(enum context_t context)
+{
+    /* if volume down is hold, boot to OF */
+    if(!read_gpio(1, 30))
+        return BOOT_OF;
+    /* on normal boot, make sure power button is hold long enough */
+    if(context == CONTEXT_NORMAL)
+    {
+        // monitor PSWITCH
+        int count = 0;
+        for(int i = 0; i < 550000; i++)
+            if(read_pswitch() == 1)
+                count++;
+        if(count < 400000)
+            return BOOT_STOP;
+    }
+    return BOOT_ROCK;
+}
+#elif defined(CREATIVE_ZENXFI2)
+static int boot_decision(int context)
+{
+    /* We are lacking buttons on the Zen X-Fi2 because on USB, the select button
+     * enters recovery mode ! So we can only use power but power is used to power up
+     * on normal boots and then select is free ! Thus use a non-uniform scheme:
+     * - normal boot/RTC:
+     *   - no key: Rockbox
+     *   - select: OF
+     * - USB boot:
+     *   - no key: Rockbox
+     *   - power: OF
+     */
+    if(context == CONTEXT_USB)
+        return read_pswitch() == 1 ? BOOT_OF : BOOT_ROCK;
+    else
+        return !read_gpio(0, 14) ? BOOT_OF : BOOT_ROCK;
+}
+#elif defined(CREATIVE_ZENXFI3)
+static int boot_decision(int context)
+{
+    /* if volume down is hold, boot to OF */
+    return !read_gpio(2, 7) ? BOOT_OF : BOOT_ROCK;
+}
+#else
+#warning You should define a target specific boot decision function
+static int boot_decision(int context)
+{
+    return BOOT_ROCK;
+}
+#endif
+
+/**
+ * Context functions
+ */
+static inline enum context_t get_context(void)
+{
+#if IMX233_SUBTARGET >= 3780
+    /* On the imx233 it's easy because we know the power up source */
+    unsigned pwrup_src = BF_RD(POWER_STS, PWRUP_SOURCE);
+    if(pwrup_src & (1 << 5))
+        return CONTEXT_USB;
+    else if(pwrup_src & (1 << 4))
+        return CONTEXT_RTC;
+    else
+        return CONTEXT_NORMAL;
+#else
+    /* On the other targets, we need to poke a few more registers */
+#endif
+}
+
+int main(uint32_t arg, uint32_t *result_id)
+{
+    switch(boot_decision(get_context()))
+    {
+        case BOOT_ROCK:
+            *result_id = arg;
+            return BOOT_ROM_SECTION;
+        case BOOT_OF:
+            return BOOT_ROM_CONTINUE;
+        case BOOT_STOP:
+        default:
+            power_down();
+    }
+}
+
+int __attribute__((section(".start"))) start(uint32_t arg, uint32_t *result_id)
+{
+    return main(arg, result_id);
+}
\ No newline at end of file
diff --git a/rbutil/mkimxboot/dualboot/dualboot.lds b/rbutil/mkimxboot/dualboot/dualboot.lds
index caaff1a41d..09739aee15 100644
--- a/rbutil/mkimxboot/dualboot/dualboot.lds
+++ b/rbutil/mkimxboot/dualboot/dualboot.lds
@@ -11,6 +11,7 @@ SECTIONS
 {
     .text 0 :
     {
+        *(.start*)
         *(.text*)
     } > OCRAM
 }