/* Teensyduino Core Library
 * http://www.pjrc.com/teensy/
 * Copyright (c) 2013 PJRC.COM, LLC.
 * Modifications by Jacob Alexander 2014
 *
 * Permission is hereby granted, free of charge, to any person obtaining
 * a copy of this software and associated documentation files (the
 * "Software"), to deal in the Software without restriction, including
 * without limitation the rights to use, copy, modify, merge, publish,
 * distribute, sublicense, and/or sell copies of the Software, and to
 * permit persons to whom the Software is furnished to do so, subject to
 * the following conditions:
 *
 * 1. The above copyright notice and this permission notice shall be
 * included in all copies or substantial portions of the Software.
 *
 * 2. If the Software is incorporated into a build system that allows
 * selection among a list of target devices, then similar target
 * devices manufactured by PJRC.COM must be included in the list of
 * target devices and selectable in the same manner.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
 * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
 * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

// Local Includes
#include "mk20dx.h"



// ----- Variables -----

extern unsigned long _stext;
extern unsigned long _etext;
extern unsigned long _sdata;
extern unsigned long _edata;
extern unsigned long _sbss;
extern unsigned long _ebss;
extern unsigned long _estack;



// ----- Function Declarations -----

extern int main ();
void ResetHandler();



// ----- Interrupts -----

// NVIC - Default ISR
void fault_isr()
{
	while ( 1 )
	{
		// keep polling some communication while in fault
		// mode, so we don't completely die.
		if ( SIM_SCGC4 & SIM_SCGC4_USBOTG ) usb_isr();
		if ( SIM_SCGC4 & SIM_SCGC4_UART0 )  uart0_status_isr();
		if ( SIM_SCGC4 & SIM_SCGC4_UART1 )  uart1_status_isr();
		if ( SIM_SCGC4 & SIM_SCGC4_UART2 )  uart2_status_isr();
	}
}

void unused_isr()
{
	fault_isr();
}


// NVIC - SysTick ISR
extern volatile uint32_t systick_millis_count;
void systick_default_isr()
{
	systick_millis_count++;
}


// NVIC - Default ISR/Vector Linking
void nmi_isr()              __attribute__ ((weak, alias("unused_isr")));
void hard_fault_isr()       __attribute__ ((weak, alias("unused_isr")));
void memmanage_fault_isr()  __attribute__ ((weak, alias("unused_isr")));
void bus_fault_isr()        __attribute__ ((weak, alias("unused_isr")));
void usage_fault_isr()      __attribute__ ((weak, alias("unused_isr")));
void svcall_isr()           __attribute__ ((weak, alias("unused_isr")));
void debugmonitor_isr()     __attribute__ ((weak, alias("unused_isr")));
void pendablesrvreq_isr()   __attribute__ ((weak, alias("unused_isr")));
void systick_isr()          __attribute__ ((weak, alias("systick_default_isr")));

void dma_ch0_isr()          __attribute__ ((weak, alias("unused_isr")));
void dma_ch1_isr()          __attribute__ ((weak, alias("unused_isr")));
void dma_ch2_isr()          __attribute__ ((weak, alias("unused_isr")));
void dma_ch3_isr()          __attribute__ ((weak, alias("unused_isr")));
void dma_ch4_isr()          __attribute__ ((weak, alias("unused_isr")));
void dma_ch5_isr()          __attribute__ ((weak, alias("unused_isr")));
void dma_ch6_isr()          __attribute__ ((weak, alias("unused_isr")));
void dma_ch7_isr()          __attribute__ ((weak, alias("unused_isr")));
void dma_ch8_isr()          __attribute__ ((weak, alias("unused_isr")));
void dma_ch9_isr()          __attribute__ ((weak, alias("unused_isr")));
void dma_ch10_isr()         __attribute__ ((weak, alias("unused_isr")));
void dma_ch11_isr()         __attribute__ ((weak, alias("unused_isr")));
void dma_ch12_isr()         __attribute__ ((weak, alias("unused_isr")));
void dma_ch13_isr()         __attribute__ ((weak, alias("unused_isr")));
void dma_ch14_isr()         __attribute__ ((weak, alias("unused_isr")));
void dma_ch15_isr()         __attribute__ ((weak, alias("unused_isr")));
void dma_error_isr()        __attribute__ ((weak, alias("unused_isr")));
void mcm_isr()              __attribute__ ((weak, alias("unused_isr")));
void flash_cmd_isr()        __attribute__ ((weak, alias("unused_isr")));
void flash_error_isr()      __attribute__ ((weak, alias("unused_isr")));
void low_voltage_isr()      __attribute__ ((weak, alias("unused_isr")));
void wakeup_isr()           __attribute__ ((weak, alias("unused_isr")));
void watchdog_isr()         __attribute__ ((weak, alias("unused_isr")));
void i2c0_isr()             __attribute__ ((weak, alias("unused_isr")));
void i2c1_isr()             __attribute__ ((weak, alias("unused_isr")));
void i2c2_isr()             __attribute__ ((weak, alias("unused_isr")));
void spi0_isr()             __attribute__ ((weak, alias("unused_isr")));
void spi1_isr()             __attribute__ ((weak, alias("unused_isr")));
void spi2_isr()             __attribute__ ((weak, alias("unused_isr")));
void sdhc_isr()             __attribute__ ((weak, alias("unused_isr")));
void can0_message_isr()     __attribute__ ((weak, alias("unused_isr")));
void can0_bus_off_isr()     __attribute__ ((weak, alias("unused_isr")));
void can0_error_isr()       __attribute__ ((weak, alias("unused_isr")));
void can0_tx_warn_isr()     __attribute__ ((weak, alias("unused_isr")));
void can0_rx_warn_isr()     __attribute__ ((weak, alias("unused_isr")));
void can0_wakeup_isr()      __attribute__ ((weak, alias("unused_isr")));
void i2s0_tx_isr()          __attribute__ ((weak, alias("unused_isr")));
void i2s0_rx_isr()          __attribute__ ((weak, alias("unused_isr")));
void uart0_lon_isr()        __attribute__ ((weak, alias("unused_isr")));
void uart0_status_isr()     __attribute__ ((weak, alias("unused_isr")));
void uart0_error_isr()      __attribute__ ((weak, alias("unused_isr")));
void uart1_status_isr()     __attribute__ ((weak, alias("unused_isr")));
void uart1_error_isr()      __attribute__ ((weak, alias("unused_isr")));
void uart2_status_isr()     __attribute__ ((weak, alias("unused_isr")));
void uart2_error_isr()      __attribute__ ((weak, alias("unused_isr")));
void uart3_status_isr()     __attribute__ ((weak, alias("unused_isr")));
void uart3_error_isr()      __attribute__ ((weak, alias("unused_isr")));
void uart4_status_isr()     __attribute__ ((weak, alias("unused_isr")));
void uart4_error_isr()      __attribute__ ((weak, alias("unused_isr")));
void uart5_status_isr()     __attribute__ ((weak, alias("unused_isr")));
void uart5_error_isr()      __attribute__ ((weak, alias("unused_isr")));
void adc0_isr()             __attribute__ ((weak, alias("unused_isr")));
void adc1_isr()             __attribute__ ((weak, alias("unused_isr")));
void cmp0_isr()             __attribute__ ((weak, alias("unused_isr")));
void cmp1_isr()             __attribute__ ((weak, alias("unused_isr")));
void cmp2_isr()             __attribute__ ((weak, alias("unused_isr")));
void ftm0_isr()             __attribute__ ((weak, alias("unused_isr")));
void ftm1_isr()             __attribute__ ((weak, alias("unused_isr")));
void ftm2_isr()             __attribute__ ((weak, alias("unused_isr")));
void ftm3_isr()             __attribute__ ((weak, alias("unused_isr")));
void cmt_isr()              __attribute__ ((weak, alias("unused_isr")));
void rtc_alarm_isr()        __attribute__ ((weak, alias("unused_isr")));
void rtc_seconds_isr()      __attribute__ ((weak, alias("unused_isr")));
void pit0_isr()             __attribute__ ((weak, alias("unused_isr")));
void pit1_isr()             __attribute__ ((weak, alias("unused_isr")));
void pit2_isr()             __attribute__ ((weak, alias("unused_isr")));
void pit3_isr()             __attribute__ ((weak, alias("unused_isr")));
void pdb_isr()              __attribute__ ((weak, alias("unused_isr")));
void usb_isr()              __attribute__ ((weak, alias("unused_isr")));
void usb_charge_isr()       __attribute__ ((weak, alias("unused_isr")));
void dac0_isr()             __attribute__ ((weak, alias("unused_isr")));
void dac1_isr()             __attribute__ ((weak, alias("unused_isr")));
void tsi0_isr()             __attribute__ ((weak, alias("unused_isr")));
void mcg_isr()              __attribute__ ((weak, alias("unused_isr")));
void lptmr_isr()            __attribute__ ((weak, alias("unused_isr")));
void porta_isr()            __attribute__ ((weak, alias("unused_isr")));
void portb_isr()            __attribute__ ((weak, alias("unused_isr")));
void portc_isr()            __attribute__ ((weak, alias("unused_isr")));
void portd_isr()            __attribute__ ((weak, alias("unused_isr")));
void porte_isr()            __attribute__ ((weak, alias("unused_isr")));
void software_isr()         __attribute__ ((weak, alias("unused_isr")));


// NVIC - Interrupt Vector Table
__attribute__ ((section(".vectors"), used))
void (* const gVectors[])() =
{
	(void (*)(void))((unsigned long)&_estack),      //  0 ARM: Initial Stack Pointer
	ResetHandler,                                   //  1 ARM: Initial Program Counter
	nmi_isr,                                        //  2 ARM: Non-maskable Interrupt (NMI)
	hard_fault_isr,                                 //  3 ARM: Hard Fault
	memmanage_fault_isr,                            //  4 ARM: MemManage Fault
	bus_fault_isr,                                  //  5 ARM: Bus Fault
	usage_fault_isr,                                //  6 ARM: Usage Fault
	fault_isr,                                      //  7 --
	fault_isr,                                      //  8 --
	fault_isr,                                      //  9 --
	fault_isr,                                      // 10 --
	svcall_isr,                                     // 11 ARM: Supervisor call (SVCall)
	debugmonitor_isr,                               // 12 ARM: Debug Monitor
	fault_isr,                                      // 13 --
	pendablesrvreq_isr,                             // 14 ARM: Pendable req serv(PendableSrvReq)
	systick_isr,                                    // 15 ARM: System tick timer (SysTick)
#if defined(_mk20dx128_) || defined(_mk20dx128vlf5_)
	dma_ch0_isr,                                    // 16 DMA channel 0 transfer complete
	dma_ch1_isr,                                    // 17 DMA channel 1 transfer complete
	dma_ch2_isr,                                    // 18 DMA channel 2 transfer complete
	dma_ch3_isr,                                    // 19 DMA channel 3 transfer complete
	dma_error_isr,                                  // 20 DMA error interrupt channel
	unused_isr,                                     // 21 DMA --
	flash_cmd_isr,                                  // 22 Flash Memory Command complete
	flash_error_isr,                                // 23 Flash Read collision
	low_voltage_isr,                                // 24 Low-voltage detect/warning
	wakeup_isr,                                     // 25 Low Leakage Wakeup
	watchdog_isr,                                   // 26 Both EWM and WDOG interrupt
	i2c0_isr,                                       // 27 I2C0
	spi0_isr,                                       // 28 SPI0
	i2s0_tx_isr,                                    // 29 I2S0 Transmit
	i2s0_rx_isr,                                    // 30 I2S0 Receive
	uart0_lon_isr,                                  // 31 UART0 CEA709.1-B (LON) status
	uart0_status_isr,                               // 32 UART0 status
	uart0_error_isr,                                // 33 UART0 error
	uart1_status_isr,                               // 34 UART1 status
	uart1_error_isr,                                // 35 UART1 error
	uart2_status_isr,                               // 36 UART2 status
	uart2_error_isr,                                // 37 UART2 error
	adc0_isr,                                       // 38 ADC0
	cmp0_isr,                                       // 39 CMP0
	cmp1_isr,                                       // 40 CMP1
	ftm0_isr,                                       // 41 FTM0
	ftm1_isr,                                       // 42 FTM1
	cmt_isr,                                        // 43 CMT
	rtc_alarm_isr,                                  // 44 RTC Alarm interrupt
	rtc_seconds_isr,                                // 45 RTC Seconds interrupt
	pit0_isr,                                       // 46 PIT Channel 0
	pit1_isr,                                       // 47 PIT Channel 1
	pit2_isr,                                       // 48 PIT Channel 2
	pit3_isr,                                       // 49 PIT Channel 3
	pdb_isr,                                        // 50 PDB Programmable Delay Block
	usb_isr,                                        // 51 USB OTG
	usb_charge_isr,                                 // 52 USB Charger Detect
	tsi0_isr,                                       // 53 TSI0
	mcg_isr,                                        // 54 MCG
	lptmr_isr,                                      // 55 Low Power Timer
	porta_isr,                                      // 56 Pin detect (Port A)
	portb_isr,                                      // 57 Pin detect (Port B)
	portc_isr,                                      // 58 Pin detect (Port C)
	portd_isr,                                      // 59 Pin detect (Port D)
	porte_isr,                                      // 60 Pin detect (Port E)
	software_isr,                                   // 61 Software interrupt
#elif defined(_mk20dx256_)
	dma_ch0_isr,                                    // 16 DMA channel 0 transfer complete
	dma_ch1_isr,                                    // 17 DMA channel 1 transfer complete
	dma_ch2_isr,                                    // 18 DMA channel 2 transfer complete
	dma_ch3_isr,                                    // 19 DMA channel 3 transfer complete
	dma_ch4_isr,                                    // 20 DMA channel 4 transfer complete
	dma_ch5_isr,                                    // 21 DMA channel 5 transfer complete
	dma_ch6_isr,                                    // 22 DMA channel 6 transfer complete
	dma_ch7_isr,                                    // 23 DMA channel 7 transfer complete
	dma_ch8_isr,                                    // 24 DMA channel 8 transfer complete
	dma_ch9_isr,                                    // 25 DMA channel 9 transfer complete
	dma_ch10_isr,                                   // 26 DMA channel 10 transfer complete
	dma_ch11_isr,                                   // 27 DMA channel 10 transfer complete
	dma_ch12_isr,                                   // 28 DMA channel 10 transfer complete
	dma_ch13_isr,                                   // 29 DMA channel 10 transfer complete
	dma_ch14_isr,                                   // 30 DMA channel 10 transfer complete
	dma_ch15_isr,                                   // 31 DMA channel 10 transfer complete
	dma_error_isr,                                  // 32 DMA error interrupt channel
	unused_isr,                                     // 33 --
	flash_cmd_isr,                                  // 34 Flash Memory Command complete
	flash_error_isr,                                // 35 Flash Read collision
	low_voltage_isr,                                // 36 Low-voltage detect/warning
	wakeup_isr,                                     // 37 Low Leakage Wakeup
	watchdog_isr,                                   // 38 Both EWM and WDOG interrupt
	unused_isr,                                     // 39 --
	i2c0_isr,                                       // 40 I2C0
	i2c1_isr,                                       // 41 I2C1
	spi0_isr,                                       // 42 SPI0
	spi1_isr,                                       // 43 SPI1
	unused_isr,                                     // 44 --
	can0_message_isr,                               // 45 CAN OR'ed Message buffer (0-15)
	can0_bus_off_isr,                               // 46 CAN Bus Off
	can0_error_isr,                                 // 47 CAN Error
	can0_tx_warn_isr,                               // 48 CAN Transmit Warning
	can0_rx_warn_isr,                               // 49 CAN Receive Warning
	can0_wakeup_isr,                                // 50 CAN Wake Up
	i2s0_tx_isr,                                    // 51 I2S0 Transmit
	i2s0_rx_isr,                                    // 52 I2S0 Receive
	unused_isr,                                     // 53 --
	unused_isr,                                     // 54 --
	unused_isr,                                     // 55 --
	unused_isr,                                     // 56 --
	unused_isr,                                     // 57 --
	unused_isr,                                     // 58 --
	unused_isr,                                     // 59 --
	uart0_lon_isr,                                  // 60 UART0 CEA709.1-B (LON) status
	uart0_status_isr,                               // 61 UART0 status
	uart0_error_isr,                                // 62 UART0 error
	uart1_status_isr,                               // 63 UART1 status
	uart1_error_isr,                                // 64 UART1 error
	uart2_status_isr,                               // 65 UART2 status
	uart2_error_isr,                                // 66 UART2 error
	unused_isr,                                     // 67 --
	unused_isr,                                     // 68 --
	unused_isr,                                     // 69 --
	unused_isr,                                     // 70 --
	unused_isr,                                     // 71 --
	unused_isr,                                     // 72 --
	adc0_isr,                                       // 73 ADC0
	adc1_isr,                                       // 74 ADC1
	cmp0_isr,                                       // 75 CMP0
	cmp1_isr,                                       // 76 CMP1
	cmp2_isr,                                       // 77 CMP2
	ftm0_isr,                                       // 78 FTM0
	ftm1_isr,                                       // 79 FTM1
	ftm2_isr,                                       // 80 FTM2
	cmt_isr,                                        // 81 CMT
	rtc_alarm_isr,                                  // 82 RTC Alarm interrupt
	rtc_seconds_isr,                                // 83 RTC Seconds interrupt
	pit0_isr,                                       // 84 PIT Channel 0
	pit1_isr,                                       // 85 PIT Channel 1
	pit2_isr,                                       // 86 PIT Channel 2
	pit3_isr,                                       // 87 PIT Channel 3
	pdb_isr,                                        // 88 PDB Programmable Delay Block
	usb_isr,                                        // 89 USB OTG
	usb_charge_isr,                                 // 90 USB Charger Detect
	unused_isr,                                     // 91 --
	unused_isr,                                     // 92 --
	unused_isr,                                     // 93 --
	unused_isr,                                     // 94 --
	unused_isr,                                     // 95 --
	unused_isr,                                     // 96 --
	dac0_isr,                                       // 97 DAC0
	unused_isr,                                     // 98 --
	tsi0_isr,                                       // 99 TSI0
	mcg_isr,                                        // 100 MCG
	lptmr_isr,                                      // 101 Low Power Timer
	unused_isr,                                     // 102 --
	porta_isr,                                      // 103 Pin detect (Port A)
	portb_isr,                                      // 104 Pin detect (Port B)
	portc_isr,                                      // 105 Pin detect (Port C)
	portd_isr,                                      // 106 Pin detect (Port D)
	porte_isr,                                      // 107 Pin detect (Port E)
	unused_isr,                                     // 108 --
	unused_isr,                                     // 109 --
	software_isr,                                   // 110 Software interrupt
#endif
};


// ----- Flash Configuration -----

// Only necessary for Teensy 3s, MCHCK uses the Bootloader to handle this
#if defined(_mk20dx128_) || defined(_mk20dx256_)
__attribute__ ((section(".flashconfig"), used))
const uint8_t flashconfigbytes[16] = {
	0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
	0xFF, 0xFF, 0xFF, 0xFF, 0xFE, 0xFF, 0xFF, 0xFF
};
#endif



// ----- Chip Entry Point -----

__attribute__ ((section(".startup")))
void ResetHandler()
{
	uint32_t *src = &_etext;
	uint32_t *dest = &_sdata;

	/* Disable Watchdog */
	WDOG_UNLOCK = WDOG_UNLOCK_SEQ1;
	WDOG_UNLOCK = WDOG_UNLOCK_SEQ2;
	WDOG_STCTRLH = WDOG_STCTRLH_ALLOWUPDATE;

	// enable clocks to always-used peripherals
#if defined(_mk20dx128_) || defined(_mk20dx128vlf5_)
	SIM_SCGC5 = 0x00043F82;		// clocks active to all GPIO
	SIM_SCGC6 = SIM_SCGC6_RTC | SIM_SCGC6_FTM0 | SIM_SCGC6_FTM1 | SIM_SCGC6_ADC0 | SIM_SCGC6_FTFL;
#elif defined(_mk20dx256_)
	SIM_SCGC3 = SIM_SCGC3_ADC1 | SIM_SCGC3_FTM2;
	SIM_SCGC5 = 0x00043F82;		// clocks active to all GPIO
	SIM_SCGC6 = SIM_SCGC6_RTC | SIM_SCGC6_FTM0 | SIM_SCGC6_FTM1 | SIM_SCGC6_ADC0 | SIM_SCGC6_FTFL;
#endif

#if defined(_mk20dx128_) || defined(_mk20dx256_) // Teensy 3s
	// if the RTC oscillator isn't enabled, get it started early
	if ( !(RTC_CR & RTC_CR_OSCE) )
	{
		RTC_SR = 0;
		RTC_CR = RTC_CR_SC16P | RTC_CR_SC4P | RTC_CR_OSCE;
	}
#endif

	// release I/O pins hold, if we woke up from VLLS mode
	if (PMC_REGSC & PMC_REGSC_ACKISO) PMC_REGSC |= PMC_REGSC_ACKISO;

	// Prepare RAM
	while ( dest < &_edata ) *dest++ = *src++;
	dest = &_sbss;
	while ( dest < &_ebss ) *dest++ = 0;

// MCHCK
#if defined(_mk20dx128vlf5_)
        /* FLL at 48MHz */
	MCG_C4 = MCG_C4_DMX32 | MCG_C4_DRST_DRS( 1 );

	//SIM_SOPT2 = SIM_SOPT2_PLLFLLSEL;
	SIM_SOPT2 = SIM_SOPT2_USBSRC | SIM_SOPT2_PLLFLLSEL | SIM_SOPT2_TRACECLKSEL | SIM_SOPT2_CLKOUTSEL( 6 );

// Teensy 3.0 and 3.1
#else
	unsigned int i;

	SCB_VTOR = 0;	// use vector table in flash

	// default all interrupts to medium priority level
	for ( i = 0; i < NVIC_NUM_INTERRUPTS; i++ )
	{
		NVIC_SET_PRIORITY( i, 128 );
	}

	// start in FEI mode
	// enable capacitors for crystal
	OSC0_CR = OSC_SC8P | OSC_SC2P;

	// enable osc, 8-32 MHz range, low power mode
	MCG_C2 = MCG_C2_RANGE0( 2 ) | MCG_C2_EREFS;

	// switch to crystal as clock source, FLL input = 16 MHz / 512
	MCG_C1 =  MCG_C1_CLKS( 2 ) | MCG_C1_FRDIV( 4 );

	// wait for crystal oscillator to begin
	while ( (MCG_S & MCG_S_OSCINIT0) == 0 );

	// wait for FLL to use oscillator
	while ( (MCG_S & MCG_S_IREFST) != 0 );

	// wait for MCGOUT to use oscillator
	while ( (MCG_S & MCG_S_CLKST_MASK) != MCG_S_CLKST( 2 ) );

	// now we're in FBE mode
	// config PLL input for 16 MHz Crystal / 4 = 4 MHz
	MCG_C5 = MCG_C5_PRDIV0( 3 );

	// config PLL for 96 MHz output
	MCG_C6 = MCG_C6_PLLS | MCG_C6_VDIV0( 0 );

	// wait for PLL to start using xtal as its input
	while ( !(MCG_S & MCG_S_PLLST) );

	// wait for PLL to lock
	while ( !(MCG_S & MCG_S_LOCK0) );

	// now we're in PBE mode
#if F_CPU == 96000000
	// config divisors: 96 MHz core, 48 MHz bus, 24 MHz flash
	SIM_CLKDIV1 = SIM_CLKDIV1_OUTDIV1( 0 ) | SIM_CLKDIV1_OUTDIV2( 1 ) | SIM_CLKDIV1_OUTDIV4( 3 );
#elif F_CPU == 48000000
	// config divisors: 48 MHz core, 48 MHz bus, 24 MHz flash
	SIM_CLKDIV1 = SIM_CLKDIV1_OUTDIV1( 1 ) | SIM_CLKDIV1_OUTDIV2( 1 ) | SIM_CLKDIV1_OUTDIV4( 3 );
#elif F_CPU == 24000000
	// config divisors: 24 MHz core, 24 MHz bus, 24 MHz flash
	SIM_CLKDIV1 = SIM_CLKDIV1_OUTDIV1( 3 ) | SIM_CLKDIV1_OUTDIV2( 3 ) | SIM_CLKDIV1_OUTDIV4( 3 );
#else
#error "Error, F_CPU must be 96000000, 48000000, or 24000000"
#endif
	// switch to PLL as clock source, FLL input = 16 MHz / 512
	MCG_C1 = MCG_C1_CLKS( 0 ) | MCG_C1_FRDIV( 4 );

	// wait for PLL clock to be used
	while ( (MCG_S & MCG_S_CLKST_MASK) != MCG_S_CLKST( 3 ) );

	// now we're in PEE mode
	// configure USB for 48 MHz clock
	SIM_CLKDIV2 = SIM_CLKDIV2_USBDIV( 1 ); // USB = 96 MHz PLL / 2

	// USB uses PLL clock, trace is CPU clock, CLKOUT=OSCERCLK0
	SIM_SOPT2 = SIM_SOPT2_USBSRC | SIM_SOPT2_PLLFLLSEL | SIM_SOPT2_TRACECLKSEL | SIM_SOPT2_CLKOUTSEL( 6 );

#endif
	// Initialize the SysTick counter
	SYST_RVR = (F_CPU / 1000) - 1;
	SYST_CSR = SYST_CSR_CLKSOURCE | SYST_CSR_TICKINT | SYST_CSR_ENABLE;

	__enable_irq();

	main();
	while ( 1 ); // Shouldn't get here...
}



// ----- RAM Setup -----

char *__brkval = (char *)&_ebss;

void * _sbrk( int incr )
{
	char *prev = __brkval;
	__brkval += incr;
	return prev;
}



// ----- Interrupt Execution Priority -----

int nvic_execution_priority()
{
	int priority = 256;
	uint32_t primask, faultmask, basepri, ipsr;

	// full algorithm in ARM DDI0403D, page B1-639
	// this isn't quite complete, but hopefully good enough
	asm volatile( "mrs %0, faultmask\n" : "=r" (faultmask):: );
	if ( faultmask )
	{
		return -1;
	}

	asm volatile( "mrs %0, primask\n" : "=r" (primask):: );
	if ( primask )
	{
		return 0;
	}

	asm volatile( "mrs %0, ipsr\n" : "=r" (ipsr):: );
	if ( ipsr )
	{
		if ( ipsr < 16)
		{
			priority = 0; // could be non-zero
		}
		else
		{
			priority = NVIC_GET_PRIORITY( ipsr - 16 );
		}
	}

	asm volatile( "mrs %0, basepri\n" : "=r" (basepri):: );
	if ( basepri > 0 && basepri < priority )
	{
		priority = basepri;
	}

	return priority;
}