Merge pull request #3 from PaulStoffregen/master

resync

teensy3/SPIFIFO.h

@@ -57,6 +57,24 @@
 #define SPI_CLOCK_6MHz    (SPI_CTAR_PBR(0) | SPI_CTAR_BR(0))                //(24 / 2) * ((1+0)/2)
 #define SPI_CLOCK_4MHz    (SPI_CTAR_PBR(0) | SPI_CTAR_BR(2) | SPI_CTAR_DBR) //(24 / 2) * ((1+1)/6)
 
+#elif F_BUS == 16000000
+#define HAS_SPIFIFO
+#define SPI_CLOCK_24MHz   (SPI_CTAR_PBR(0) | SPI_CTAR_BR(3) | SPI_CTAR_DBR) //(16 / 2) * ((1+1)/8) = 2 MHz
+#define SPI_CLOCK_16MHz   (SPI_CTAR_PBR(0) | SPI_CTAR_BR(3) | SPI_CTAR_DBR) //(16 / 2) * ((1+1)/8) = 2 MHz
+#define SPI_CLOCK_12MHz   (SPI_CTAR_PBR(0) | SPI_CTAR_BR(3) | SPI_CTAR_DBR) //(16 / 2) * ((1+1)/8) = 2 MHz
+#define SPI_CLOCK_8MHz    (SPI_CTAR_PBR(0) | SPI_CTAR_BR(3) | SPI_CTAR_DBR) //(16 / 2) * ((1+1)/8) = 2 MHz
+#define SPI_CLOCK_6MHz    (SPI_CTAR_PBR(0) | SPI_CTAR_BR(3) | SPI_CTAR_DBR) //(16 / 2) * ((1+1)/8) = 2 MHz
+#define SPI_CLOCK_4MHz    (SPI_CTAR_PBR(0) | SPI_CTAR_BR(3) | SPI_CTAR_DBR) //(16 / 2) * ((1+1)/8) = 2 MHz
+
+#elif F_BUS == 8000000
+#define HAS_SPIFIFO
+#define SPI_CLOCK_24MHz   (SPI_CTAR_PBR(0) | SPI_CTAR_BR(1) | SPI_CTAR_DBR) //(8 / 2) * ((1+1)/4) = 2 MHz
+#define SPI_CLOCK_16MHz   (SPI_CTAR_PBR(0) | SPI_CTAR_BR(1) | SPI_CTAR_DBR) //(8 / 2) * ((1+1)/4) = 2 MHz
+#define SPI_CLOCK_12MHz   (SPI_CTAR_PBR(0) | SPI_CTAR_BR(1) | SPI_CTAR_DBR) //(8 / 2) * ((1+1)/4) = 2 MHz
+#define SPI_CLOCK_8MHz    (SPI_CTAR_PBR(0) | SPI_CTAR_BR(1) | SPI_CTAR_DBR) //(8 / 2) * ((1+1)/4) = 2 MHz
+#define SPI_CLOCK_6MHz    (SPI_CTAR_PBR(0) | SPI_CTAR_BR(1) | SPI_CTAR_DBR) //(8 / 2) * ((1+1)/4) = 2 MHz
+#define SPI_CLOCK_4MHz    (SPI_CTAR_PBR(0) | SPI_CTAR_BR(1) | SPI_CTAR_DBR) //(8 / 2) * ((1+1)/4) = 2 MHz
+
 #elif F_BUS == 4000000
 #define HAS_SPIFIFO
 #define SPI_CLOCK_24MHz   (SPI_CTAR_PBR(0) | SPI_CTAR_BR(0) | SPI_CTAR_DBR) //(4 / 2) * ((1+1)/2) = 2 MHz

teensy3/analog.c

@@ -71,6 +71,16 @@ static uint8_t analog_reference_internal = 0;
   #define ADC_CFG1_12BIT  ADC_CFG1_ADIV(1) + ADC_CFG1_ADICLK(0) // 12 MHz
   #define ADC_CFG1_10BIT  ADC_CFG1_ADIV(1) + ADC_CFG1_ADICLK(0) // 12 MHz
   #define ADC_CFG1_8BIT   ADC_CFG1_ADIV(0) + ADC_CFG1_ADICLK(0) // 24 MHz
+#elif F_BUS == 16000000
+  #define ADC_CFG1_16BIT  ADC_CFG1_ADIV(0) + ADC_CFG1_ADICLK(0) // 8 MHz
+  #define ADC_CFG1_12BIT  ADC_CFG1_ADIV(0) + ADC_CFG1_ADICLK(0) // 8 MHz
+  #define ADC_CFG1_10BIT  ADC_CFG1_ADIV(0) + ADC_CFG1_ADICLK(0) // 8 MHz
+  #define ADC_CFG1_8BIT   ADC_CFG1_ADIV(0) + ADC_CFG1_ADICLK(0) // 16 MHz
+#elif F_BUS == 8000000
+  #define ADC_CFG1_16BIT  ADC_CFG1_ADIV(0) + ADC_CFG1_ADICLK(0) // 8 MHz
+  #define ADC_CFG1_12BIT  ADC_CFG1_ADIV(0) + ADC_CFG1_ADICLK(0) // 8 MHz
+  #define ADC_CFG1_10BIT  ADC_CFG1_ADIV(0) + ADC_CFG1_ADICLK(0) // 8 MHz
+  #define ADC_CFG1_8BIT   ADC_CFG1_ADIV(0) + ADC_CFG1_ADICLK(0) // 8 MHz
 #elif F_BUS == 4000000
   #define ADC_CFG1_16BIT  ADC_CFG1_ADIV(0) + ADC_CFG1_ADICLK(0) // 4 MHz
   #define ADC_CFG1_12BIT  ADC_CFG1_ADIV(0) + ADC_CFG1_ADICLK(0) // 4 MHz

teensy3/core_pins.h

@@ -784,6 +784,10 @@ static inline void delayMicroseconds(uint32_t usec)
 	uint32_t n = usec << 4;
 #elif F_CPU == 24000000
 	uint32_t n = usec << 3;
+#elif F_CPU == 16000000
+	uint32_t n = usec << 2;
+#elif F_CPU == 8000000
+	uint32_t n = usec << 1;
 #elif F_CPU == 4000000
 	uint32_t n = usec;
 #elif F_CPU == 2000000
@@ -792,7 +796,7 @@ static inline void delayMicroseconds(uint32_t usec)
 	if (usec == 0) return;
 	__asm__ volatile(
 		"L_%=_delayMicroseconds:"		"\n\t"
-#if F_CPU < 10000000
+#if F_CPU < 24000000
 		"nop"					"\n\t"
 #endif
 		"subs   %0, #1"				"\n\t"

teensy3/mk20dx128.c

@@ -400,7 +400,29 @@ void ResetHandler(void)
 	// default all interrupts to medium priority level
 	for (i=0; i < NVIC_NUM_INTERRUPTS; i++) NVIC_SET_PRIORITY(i, 128);
 
-	// start in FEI mode
+
+	// hardware always starts in FEI mode
+	//  C1[CLKS] bits are written to 00
+	//  C1[IREFS] bit is written to 1
+	//  C6[PLLS] bit is written to 0
+#if F_CPU <= 4000000
+	// use the internal oscillator
+	MCG_C1 = MCG_C1_CLKS(1) | MCG_C2_IRCS;
+	// wait for MCGOUT to use oscillator
+	while ((MCG_S & MCG_S_CLKST_MASK) != MCG_S_CLKST(1)) ;
+	MCG_C2 = MCG_C2_IRCS;
+	// now in FBI mode:
+	//  C1[CLKS] bits are written to 01
+	//  C1[IREFS] bit is written to 1
+	//  C6[PLLS] is written to 0
+	//  C2[LP] is written to 0
+	MCG_C2 = MCG_C2_IRCS | MCG_C2_LP;
+	// now in BLPI mode:
+	//  C1[CLKS] bits are written to 01
+	//  C1[IREFS] bit is written to 1
+	//  C6[PLLS] bit is written to 0
+	//  C2[LP] bit is written to 1
+#else
 	// enable capacitors for crystal
 	OSC0_CR = OSC_SC8P | OSC_SC2P;
 	// enable osc, 8-32 MHz range, low power mode
@@ -413,73 +435,156 @@ void ResetHandler(void)
 	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
-#if F_CPU == 72000000
+	// now in FBE mode
+	//  C1[CLKS] bits are written to 10
+	//  C1[IREFS] bit is written to 0
+	//  C1[FRDIV] must be written to divide xtal to 31.25-39 kHz
+	//  C6[PLLS] bit is written to 0
+	//  C2[LP] is written to 0
+  #if F_CPU <= 16000000
+	// if the crystal is fast enough, use it directly (no FLL or PLL)
+	MCG_C2 = MCG_C2_RANGE0(2) | MCG_C2_EREFS | MCG_C2_LP;
+	// BLPE mode:
+	//   C1[CLKS] bits are written to 10
+	//   C1[IREFS] bit is written to 0
+	//   C2[LP] bit is written to 1
+  #else
+	// if we need faster than the crystal, turn on the PLL
+    #if F_CPU == 72000000
 	MCG_C5 = MCG_C5_PRDIV0(5);		 // config PLL input for 16 MHz Crystal / 6 = 2.667 Hz
-#else
+    #else
 	MCG_C5 = MCG_C5_PRDIV0(3);		 // config PLL input for 16 MHz Crystal / 4 = 4 MHz
-#endif
-	
-#if F_CPU == 168000000
+    #endif
+    #if F_CPU == 168000000
 	MCG_C6 = MCG_C6_PLLS | MCG_C6_VDIV0(18); // config PLL for 168 MHz output
-#elif F_CPU == 144000000
+    #elif F_CPU == 144000000
 	MCG_C6 = MCG_C6_PLLS | MCG_C6_VDIV0(12); // config PLL for 144 MHz output
-#elif F_CPU == 120000000
+    #elif F_CPU == 120000000
 	MCG_C6 = MCG_C6_PLLS | MCG_C6_VDIV0(6); // config PLL for 120 MHz output
-#elif F_CPU == 72000000
+    #elif F_CPU == 72000000
 	MCG_C6 = MCG_C6_PLLS | MCG_C6_VDIV0(3); // config PLL for 72 MHz output
-#else
+    #else
 	MCG_C6 = MCG_C6_PLLS | MCG_C6_VDIV0(0); // config PLL for 96 MHz output
-#endif
+    #endif
 	// 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
+  #endif
+#endif
 
+	// now program the clock dividers
 #if F_CPU == 168000000
-	// config divisors: 168 MHz core, 56 MHz bus, 33.6 MHz flash
+	// config divisors: 168 MHz core, 56 MHz bus, 33.6 MHz flash, USB = 168 * 2 / 7
 	SIM_CLKDIV1 = SIM_CLKDIV1_OUTDIV1(0) | SIM_CLKDIV1_OUTDIV2(2) |	 SIM_CLKDIV1_OUTDIV4(4);
+	SIM_CLKDIV2 = SIM_CLKDIV2_USBDIV(6) | SIM_CLKDIV2_USBFRAC;
 #elif F_CPU == 144000000
-	// config divisors: 144 MHz core, 48 MHz bus, 28.8 MHz flash
+	// config divisors: 144 MHz core, 48 MHz bus, 28.8 MHz flash, USB = 144 / 3
 	SIM_CLKDIV1 = SIM_CLKDIV1_OUTDIV1(0) | SIM_CLKDIV1_OUTDIV2(2) |	 SIM_CLKDIV1_OUTDIV4(4);
+	SIM_CLKDIV2 = SIM_CLKDIV2_USBDIV(2);
 #elif F_CPU == 120000000
-	// config divisors: 120 MHz core, 60 MHz bus, 24 MHz flash
+	// config divisors: 120 MHz core, 60 MHz bus, 24 MHz flash, USB = 128 * 2 / 5
 	SIM_CLKDIV1 = SIM_CLKDIV1_OUTDIV1(0) | SIM_CLKDIV1_OUTDIV2(1) |	 SIM_CLKDIV1_OUTDIV4(4);
+	SIM_CLKDIV2 = SIM_CLKDIV2_USBDIV(4) | SIM_CLKDIV2_USBFRAC;
 #elif F_CPU == 96000000
-	// config divisors: 96 MHz core, 48 MHz bus, 24 MHz flash
+	// config divisors: 96 MHz core, 48 MHz bus, 24 MHz flash, USB = 96 / 2
 	SIM_CLKDIV1 = SIM_CLKDIV1_OUTDIV1(0) | SIM_CLKDIV1_OUTDIV2(1) |	 SIM_CLKDIV1_OUTDIV4(3);
+	SIM_CLKDIV2 = SIM_CLKDIV2_USBDIV(1);
 #elif F_CPU == 72000000
-	// config divisors: 72 MHz core, 36 MHz bus, 24 MHz flash
+	// config divisors: 72 MHz core, 36 MHz bus, 24 MHz flash, USB = 72 * 2 / 3
 	SIM_CLKDIV1 = SIM_CLKDIV1_OUTDIV1(0) | SIM_CLKDIV1_OUTDIV2(1) |	 SIM_CLKDIV1_OUTDIV4(2);
+	SIM_CLKDIV2 = SIM_CLKDIV2_USBDIV(2) | SIM_CLKDIV2_USBFRAC;
 #elif F_CPU == 48000000
-	// config divisors: 48 MHz core, 48 MHz bus, 24 MHz flash
+	// config divisors: 48 MHz core, 48 MHz bus, 24 MHz flash, USB = 96 / 2
 	SIM_CLKDIV1 = SIM_CLKDIV1_OUTDIV1(1) | SIM_CLKDIV1_OUTDIV2(1) |	 SIM_CLKDIV1_OUTDIV4(3);
+	SIM_CLKDIV2 = SIM_CLKDIV2_USBDIV(1);
 #elif F_CPU == 24000000
-	// config divisors: 24 MHz core, 24 MHz bus, 24 MHz flash
+	// config divisors: 24 MHz core, 24 MHz bus, 24 MHz flash, USB = 96 / 2
 	SIM_CLKDIV1 = SIM_CLKDIV1_OUTDIV1(3) | SIM_CLKDIV1_OUTDIV2(3) |	 SIM_CLKDIV1_OUTDIV4(3);
+	SIM_CLKDIV2 = SIM_CLKDIV2_USBDIV(1);
+#elif F_CPU == 16000000
+	// config divisors: 16 MHz core, 16 MHz bus, 16 MHz flash
+	SIM_CLKDIV1 = SIM_CLKDIV1_OUTDIV1(0) | SIM_CLKDIV1_OUTDIV2(0) |	 SIM_CLKDIV1_OUTDIV4(0);
+#elif F_CPU == 8000000
+	// config divisors: 8 MHz core, 8 MHz bus, 8 MHz flash
+	SIM_CLKDIV1 = SIM_CLKDIV1_OUTDIV1(1) | SIM_CLKDIV1_OUTDIV2(1) |	 SIM_CLKDIV1_OUTDIV4(1);
+#elif F_CPU == 4000000
+	// config divisors: 4 MHz core, 4 MHz bus, 2 MHz flash
+	SIM_CLKDIV1 = SIM_CLKDIV1_OUTDIV1(0) | SIM_CLKDIV1_OUTDIV2(0) |	 SIM_CLKDIV1_OUTDIV4(1);
+#elif F_CPU == 2000000
+	// config divisors: 2 MHz core, 2 MHz bus, 1 MHz flash
+	SIM_CLKDIV1 = SIM_CLKDIV1_OUTDIV1(1) | SIM_CLKDIV1_OUTDIV2(1) |	 SIM_CLKDIV1_OUTDIV4(3);
 #else
-#error "Error, F_CPU must be 168, 144, 120, 96, 72, 48, or 24 MHz"
+#error "Error, F_CPU must be 168, 144, 120, 96, 72, 48, 24, 16, 8, 4, or 2 MHz"
 #endif
+
+#if F_CPU > 16000000
 	// 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
-#if F_CPU == 168000000
-	SIM_CLKDIV2 = SIM_CLKDIV2_USBDIV(6) | SIM_CLKDIV2_USBFRAC; // USB = 168 MHz PLL * 2 / 7
-#elif F_CPU == 144000000
-	SIM_CLKDIV2 = SIM_CLKDIV2_USBDIV(2);                       // USB = 144 MHz PLL / 3
-#elif F_CPU == 120000000
-	SIM_CLKDIV2 = SIM_CLKDIV2_USBDIV(4) | SIM_CLKDIV2_USBFRAC; // USB = 120 MHz PLL * 2 / 5
-#elif F_CPU == 72000000
-	SIM_CLKDIV2 = SIM_CLKDIV2_USBDIV(2) | SIM_CLKDIV2_USBFRAC; // USB = 72 MHz PLL * 2 / 3
-#else
-	SIM_CLKDIV2 = SIM_CLKDIV2_USBDIV(1);                       // USB = 96 MHz PLL / 2
-#endif	
 	// 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);
+#else
+	SIM_SOPT2 = SIM_SOPT2_TRACECLKSEL | SIM_SOPT2_CLKOUTSEL(3);
+#endif
+
+
+#if F_CPU <= 2000000
+	// TODO: switch to VLPR mode....
+	SMC_PMPROT = SMC_PMPROT_AVLP | SMC_PMPROT_ALLS | SMC_PMPROT_AVLLS;
+	SMC_PMCTRL = SMC_PMCTRL_RUNM(2) | SMC_PMCTRL_STOPM(2); // VLPR mode :-)
+#endif
+
+
+
+#if 0
+#if F_CPU == 2000000
+	// select external reference clock as MCG_OUT
+	MCG_C1 |= MCG_C1_CLKS(2);
+	// wait for FLL clock to be used
+	while ((MCG_S & MCG_S_CLKST_MASK) != MCG_S_CLKST(2)) ;
+	// now move to FBE mode
+	// make sure the FRDIV is configured to keep the FLL reference within spec.
+	MCG_C1 &= ~0x38; // clear FRDIV field
+	MCG_C1 |= MCG_C1_FRDIV(4); // set FLL ref divider to 512
+	MCG_C6 &= ~MCG_C6_PLLS; // clear PLLS to select the FLL
+	while (MCG_S & MCG_S_PLLST){} // Wait for PLLST status bit to clear to
+	// indicate switch to FLL output
+	// now move to FBI mode
+	MCG_C2 |= MCG_C2_IRCS; // set the IRCS bit to select the fast IRC
+	// set CLKS to 1 to select the internal reference clock
+	// keep FRDIV at existing value to keep FLL ref clock in spec.
+	// set IREFS to 1 to select internal reference clock
+	MCG_C1 = MCG_C1_CLKS(1) | MCG_C1_FRDIV(4) | MCG_C1_IREFS;
+	// wait for internal reference to be selected
+	while (!(MCG_S & MCG_S_IREFST)){}
+	// wait for fast internal reference to be selected
+	while (!(MCG_S & MCG_S_IRCST)){}
+	// wait for clock to switch to IRC
+	while ((MCG_S & MCG_S_CLKST_MASK) != MCG_S_CLKST(1)) ;
+	// now move to BLPI
+	MCG_C2 |= MCG_C2_LP;
+	// now we're in BLPI mode
+#elif F_CPU == 16000000 || F_CPU == 8000000 || F_CPU == 4000000
+	// select external reference clock as MCG_OUT
+	MCG_C1 = MCG_C1_CLKS(2);
+	// wait for external clock to be used
+	while ((MCG_S & MCG_S_CLKST_MASK) != MCG_S_CLKST(2)) ;
+	// set the LP bit to enter BLPE
+	MCG_C2 |= MCG_C2_LP;
+	// now we're in BLPE mode
+#else
+	// 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
+#endif
+#endif
 
 	// initialize the SysTick counter
 	SYST_RVR = (F_CPU / 1000) - 1;

teensy3/mk20dx128.h

@@ -63,6 +63,18 @@
 #elif (F_CPU == 24000000)
  #define F_BUS 24000000
  #define F_MEM 24000000
+#elif (F_CPU == 16000000)
+ #define F_BUS 16000000
+ #define F_MEM 16000000
+#elif (F_CPU == 8000000)
+ #define F_BUS 8000000
+ #define F_MEM 8000000
+#elif (F_CPU == 4000000)
+ #define F_BUS 4000000
+ #define F_MEM 4000000
+#elif (F_CPU == 2000000)
+ #define F_BUS 2000000
+ #define F_MEM 1000000
 #endif
 
 
@@ -640,9 +652,21 @@ extern "C" {
 #define DMA_DCHPRI2		*(volatile uint8_t  *)0x40008101 // Channel n Priority Register
 #define DMA_DCHPRI1		*(volatile uint8_t  *)0x40008102 // Channel n Priority Register
 #define DMA_DCHPRI0		*(volatile uint8_t  *)0x40008103 // Channel n Priority Register
-#define DMA_DCHPRI_CHPRI(n)		((uint8_t)(n & 3)<<0)	// Channel Arbitration Priority
+#define DMA_DCHPRI_CHPRI(n)		((uint8_t)(n & 15)<<0)	// Channel Arbitration Priority
 #define DMA_DCHPRI_DPA			((uint8_t)1<<6)		// Disable PreEmpt Ability
 #define DMA_DCHPRI_ECP			((uint8_t)1<<7)		// Enable PreEmption
+#define DMA_DCHPRI7		*(volatile uint8_t  *)0x40008104 // Channel n Priority Register
+#define DMA_DCHPRI6		*(volatile uint8_t  *)0x40008105 // Channel n Priority Register
+#define DMA_DCHPRI5		*(volatile uint8_t  *)0x40008106 // Channel n Priority Register
+#define DMA_DCHPRI4		*(volatile uint8_t  *)0x40008107 // Channel n Priority Register
+#define DMA_DCHPRI11		*(volatile uint8_t  *)0x40008108 // Channel n Priority Register
+#define DMA_DCHPRI10		*(volatile uint8_t  *)0x40008109 // Channel n Priority Register
+#define DMA_DCHPRI9		*(volatile uint8_t  *)0x4000810A // Channel n Priority Register
+#define DMA_DCHPRI8		*(volatile uint8_t  *)0x4000810B // Channel n Priority Register
+#define DMA_DCHPRI15		*(volatile uint8_t  *)0x4000810C // Channel n Priority Register
+#define DMA_DCHPRI14		*(volatile uint8_t  *)0x4000810D // Channel n Priority Register
+#define DMA_DCHPRI13		*(volatile uint8_t  *)0x4000810E // Channel n Priority Register
+#define DMA_DCHPRI12		*(volatile uint8_t  *)0x4000810F // Channel n Priority Register
 
 
 #define DMA_TCD_ATTR_SMOD(n)		(((n) & 0x1F) << 11)

teensy3/pins_teensy.c

@@ -339,6 +339,12 @@ extern void usb_init(void);
 #elif F_BUS == 24000000
 #define DEFAULT_FTM_MOD (49152 - 1)
 #define DEFAULT_FTM_PRESCALE 0
+#elif F_BUS == 16000000
+#define DEFAULT_FTM_MOD (32768 - 1)
+#define DEFAULT_FTM_PRESCALE 0
+#elif F_BUS == 8000000
+#define DEFAULT_FTM_MOD (16384 - 1)
+#define DEFAULT_FTM_PRESCALE 0
 #elif F_BUS == 4000000
 #define DEFAULT_FTM_MOD (8192 - 1)
 #define DEFAULT_FTM_PRESCALE 0
@@ -719,6 +725,10 @@ void delay(uint32_t ms)
 #define PULSEIN_LOOPS_PER_USEC 7
 #elif F_CPU == 24000000
 #define PULSEIN_LOOPS_PER_USEC 4
+#elif F_CPU == 16000000
+#define PULSEIN_LOOPS_PER_USEC 1
+#elif F_CPU == 8000000
+#define PULSEIN_LOOPS_PER_USEC 1
 #elif F_CPU == 4000000
 #define PULSEIN_LOOPS_PER_USEC 1
 #elif F_CPU == 2000000

teensy3/usb_desc.c

@@ -28,6 +28,8 @@
  * SOFTWARE.
  */
 
+#if F_CPU >= 20000000
+
 #include "usb_desc.h"
 #include "usb_names.h"
 #include "mk20dx128.h"
@@ -890,4 +892,4 @@ const uint8_t usb_endpoint_config_table[NUM_ENDPOINTS] =
 
 
 
-
+#endif // F_CPU >= 20 MHz

teensy3/usb_desc.h

@@ -31,6 +31,8 @@
 #ifndef _usb_desc_h_
 #define _usb_desc_h_
 
+#if F_CPU >= 20000000
+
 // This header is NOT meant to be included when compiling
 // user sketches in Arduino.  The low-level functions
 // provided by usb_dev.c are meant to be called only by
@@ -306,4 +308,6 @@ typedef struct {
 extern const usb_descriptor_list_t usb_descriptor_list[];
 
 
+#endif // F_CPU >= 20 MHz
+
 #endif

teensy3/usb_dev.c

@@ -28,6 +28,8 @@
  * SOFTWARE.
  */
 
+#if F_CPU >= 20000000
+
 #include "mk20dx128.h"
 //#include "HardwareSerial.h"
 #include "usb_dev.h"
@@ -969,4 +971,10 @@ void usb_init(void)
 }
 
 
+#else // F_CPU < 20 MHz
+
+void usb_init(void)
+{
+}
 
+#endif // F_CPU >= 20 MHz

teensy3/usb_dev.h

@@ -31,6 +31,8 @@
 #ifndef _usb_dev_h_
 #define _usb_dev_h_
 
+#if F_CPU >= 20000000
+
 // This header is NOT meant to be included when compiling
 // user sketches in Arduino.  The low-level functions
 // provided by usb_dev.c are meant to be called only by
@@ -101,5 +103,6 @@ extern void usb_flightsim_flush_callback(void);
 #endif
 
 
+#endif // F_CPU >= 20 MHz
 
 #endif

teensy3/usb_inst.cpp

@@ -30,6 +30,8 @@
 
 #include "WProgram.h"
 
+#if F_CPU >= 20000000
+
 #ifdef USB_SERIAL
 usb_serial_class Serial;
 #endif
@@ -65,3 +67,13 @@ FlightSimClass FlightSim;
 usb_seremu_class Serial;
 #endif
 
+
+#else // F_CPU < 20 MHz
+
+#if defined(USB_SERIAL) || defined(USB_SERIAL_HID)
+usb_serial_class Serial;
+#else
+usb_seremu_class Serial;
+#endif
+
+#endif // F_CPU

teensy3/usb_mem.c

@@ -28,6 +28,8 @@
  * SOFTWARE.
  */
 
+#if F_CPU >= 20000000
+
 #include "mk20dx128.h"
 //#include "HardwareSerial.h"
 #include "usb_dev.h"
@@ -104,3 +106,4 @@ void usb_free(usb_packet_t *p)
 	//serial_print("\n");
 }
 
+#endif // F_CPU >= 20 MHz

teensy3/usb_seremu.c

@@ -28,6 +28,8 @@
  * SOFTWARE.
  */
 
+#if F_CPU >= 20000000
+
 //#include "mk20dx128.h"
 #include "usb_dev.h"
 #include "usb_seremu.h"
@@ -256,3 +258,5 @@ void usb_seremu_flush_callback(void)
 }
 
 #endif // SEREMU_INTERFACE
+
+#endif // F_CPU >= 20 MHz

teensy3/usb_seremu.h

@@ -35,6 +35,8 @@
 
 #include <inttypes.h>
 
+#if F_CPU >= 20000000
+
 // C language implementation
 #ifdef __cplusplus
 extern "C" {
@@ -53,7 +55,6 @@ extern volatile uint8_t usb_configuration;
 }
 #endif
 
-
 // C++ interface
 #ifdef __cplusplus
 #include "Stream.h"
@@ -82,10 +83,48 @@ public:
         uint8_t rts(void) { return 1; }
         operator bool() { return usb_configuration; }
 };
-
 extern usb_seremu_class Serial;
+#endif // __cplusplus
+
 
+
+#else  // F_CPU < 20 MHz
+
+// Allow Arduino programs using Serial to compile, but Serial will do nothing.
+#ifdef __cplusplus
+#include "Stream.h"
+class usb_seremu_class : public Stream
+{
+public:
+	void begin(long) { };
+	void end() { };
+	virtual int available() { return 0; }
+	virtual int read() { return -1; }
+	virtual int peek() { return -1; }
+	virtual void flush() { }
+	virtual size_t write(uint8_t c) { return 1; }
+	virtual size_t write(const uint8_t *buffer, size_t size) { return size; }
+	size_t write(unsigned long n) { return 1; }
+	size_t write(long n) { return 1; }
+	size_t write(unsigned int n) { return 1; }
+	size_t write(int n) { return 1; }
+	using Print::write;
+	void send_now(void) { }
+	uint32_t baud(void) { return 0; }
+	uint8_t stopbits(void) { return 1; }
+	uint8_t paritytype(void) { return 0; }
+	uint8_t numbits(void) { return 8; }
+	uint8_t dtr(void) { return 1; }
+	uint8_t rts(void) { return 1; }
+	operator bool() { return true; }
+};
+
+extern usb_seremu_class Serial;
 #endif // __cplusplus
 
+
+#endif // F_CPU >= 20 MHz
+
 #endif // USB_HID
+
 #endif // USBseremu_h_

teensy3/usb_serial.h

@@ -35,6 +35,8 @@
 
 #include <inttypes.h>
 
+#if F_CPU >= 20000000
+
 // C language implementation
 #ifdef __cplusplus
 extern "C" {
@@ -58,7 +60,6 @@ extern volatile uint8_t usb_configuration;
 #define USB_SERIAL_DTR  0x01
 #define USB_SERIAL_RTS  0x02
 
-
 // C++ interface
 #ifdef __cplusplus
 #include "Stream.h"
@@ -98,10 +99,46 @@ public:
 	}
 
 };
-
 extern usb_serial_class Serial;
+#endif // __cplusplus
+
 
+#else  // F_CPU < 20 MHz
+
+// Allow Arduino programs using Serial to compile, but Serial will do nothing.
+#ifdef __cplusplus
+#include "Stream.h"
+class usb_serial_class : public Stream
+{
+public:
+        void begin(long) { };
+        void end() { };
+        virtual int available() { return 0; }
+        virtual int read() { return -1; }
+        virtual int peek() { return -1; }
+        virtual void flush() { }
+        virtual size_t write(uint8_t c) { return 1; }
+        virtual size_t write(const uint8_t *buffer, size_t size) { return size; }
+	size_t write(unsigned long n) { return 1; }
+	size_t write(long n) { return 1; }
+	size_t write(unsigned int n) { return 1; }
+	size_t write(int n) { return 1; }
+	using Print::write;
+        void send_now(void) { }
+        uint32_t baud(void) { return 0; }
+        uint8_t stopbits(void) { return 1; }
+        uint8_t paritytype(void) { return 0; }
+        uint8_t numbits(void) { return 8; }
+        uint8_t dtr(void) { return 1; }
+        uint8_t rts(void) { return 1; }
+        operator bool() { return true; }
+};
+
+extern usb_serial_class Serial;
 #endif // __cplusplus
 
+#endif // F_CPU
+
 #endif // USB_SERIAL || USB_SERIAL_HID
+
 #endif // USBserial_h_