sam: add support for Atmel SAMD21 based ItsyBitsy M0

Signed-off-by: Ron Evans <[email protected]>

1 files changed, 285 insertions, 0 deletions

diff --git a/src/runtime/runtime_atsamd21g18.go b/src/runtime/runtime_atsamd21g18.go
new file mode 100644
index 000000000..6de9ce54d
--- /dev/null
+++ b/src/runtime/runtime_atsamd21g18.go
@@ -0,0 +1,285 @@
+// +build sam,atsamd21g18a
+
+package runtime
+
+import (
+	"device/arm"
+	"device/sam"
+	"unsafe"
+)
+
+type timeUnit int64
+
+//go:export Reset_Handler
+func main() {
+	preinit()
+	initAll()
+	mainWrapper()
+	abort()
+}
+
+func init() {
+	initClocks()
+	initRTC()
+
+	// Turn on clock to SERCOM0 for Serial
+	sam.PM.APBCMASK |= sam.PM_APBCMASK_SERCOM0_
+
+	// TODO: connect to UART
+}
+
+func putchar(c byte) {
+	// TODO: write byte to UART
+	//machine.UART0.WriteByte(c)
+}
+
+func initClocks() {
+	// Set 1 Flash Wait State for 48MHz, required for 3.3V operation according to SAMD21 Datasheet
+	sam.NVMCTRL.CTRLB |= (sam.NVMCTRL_CTRLB_RWS_HALF << sam.NVMCTRL_CTRLB_RWS_Pos)
+
+	// Turn on the digital interface clock
+	sam.PM.APBAMASK |= sam.PM_APBAMASK_GCLK_
+	// turn off RTC
+	sam.PM.APBAMASK &^= sam.PM_APBAMASK_RTC_
+
+	// Enable OSC32K clock (Internal 32.768Hz oscillator).
+	// This requires registers that are not included in the SVD file.
+	// This is from samd21g18a.h and nvmctrl.h:
+	//
+	// #define NVMCTRL_OTP4 0x00806020
+	//
+	// #define SYSCTRL_FUSES_OSC32K_CAL_ADDR (NVMCTRL_OTP4 + 4)
+	// #define SYSCTRL_FUSES_OSC32K_CAL_Pos 6 /** (NVMCTRL_OTP4) OSC32K Calibration */
+	// #define SYSCTRL_FUSES_OSC32K_CAL_Msk (0x7Fu << SYSCTRL_FUSES_OSC32K_CAL_Pos)
+	// #define SYSCTRL_FUSES_OSC32K_CAL(value) ((SYSCTRL_FUSES_OSC32K_CAL_Msk & ((value) << SYSCTRL_FUSES_OSC32K_CAL_Pos)))
+	// u32_t fuse = *(u32_t *)FUSES_OSC32K_CAL_ADDR;
+	// u32_t calib = (fuse & FUSES_OSC32K_CAL_Msk) >> FUSES_OSC32K_CAL_Pos;
+	fuse := *(*uint32)(unsafe.Pointer(uintptr(0x00806020) + 4))
+	calib := (fuse & uint32(0x7f<<6)) >> 6
+
+	// SYSCTRL_OSC32K_CALIB(calib) |
+	//  SYSCTRL_OSC32K_STARTUP(0x6u) |
+	//  SYSCTRL_OSC32K_EN32K | SYSCTRL_OSC32K_ENABLE;
+	sam.SYSCTRL.OSC32K = sam.RegValue((calib << sam.SYSCTRL_OSC32K_CALIB_Pos) |
+		(0x6 << sam.SYSCTRL_OSC32K_STARTUP_Pos) |
+		sam.SYSCTRL_OSC32K_EN32K |
+		sam.SYSCTRL_OSC32K_EN1K |
+		sam.SYSCTRL_OSC32K_ENABLE)
+	// Wait for oscillator stabilization
+	for (sam.SYSCTRL.PCLKSR & sam.SYSCTRL_PCLKSR_OSC32KRDY) == 0 {
+	}
+
+	// Software reset the module to ensure it is re-initialized correctly
+	sam.GCLK.CTRL = sam.GCLK_CTRL_SWRST
+	// Wait for reset to complete
+	for (sam.GCLK.CTRL&sam.GCLK_CTRL_SWRST) > 0 && (sam.GCLK.STATUS&sam.GCLK_STATUS_SYNCBUSY) > 0 {
+	}
+
+	// Put OSC32K as source of Generic Clock Generator 1
+	sam.GCLK.GENDIV = sam.RegValue((1 << sam.GCLK_GENDIV_ID_Pos) |
+		(0 << sam.GCLK_GENDIV_DIV_Pos))
+	waitForSync()
+
+	// GCLK_GENCTRL_ID(1) | GCLK_GENCTRL_SRC_OSC32K | GCLK_GENCTRL_GENEN;
+	sam.GCLK.GENCTRL = sam.RegValue((1 << sam.GCLK_GENCTRL_ID_Pos) |
+		(sam.GCLK_GENCTRL_SRC_OSC32K << sam.GCLK_GENCTRL_SRC_Pos) |
+		sam.GCLK_GENCTRL_GENEN)
+	waitForSync()
+
+	// Use Generic Clock Generator 1 as source for Generic Clock Multiplexer 0 (DFLL48M reference)
+	sam.GCLK.CLKCTRL = sam.RegValue16((sam.GCLK_CLKCTRL_ID_DFLL48 << sam.GCLK_CLKCTRL_ID_Pos) |
+		(sam.GCLK_CLKCTRL_GEN_GCLK1 << sam.GCLK_CLKCTRL_GEN_Pos) |
+		sam.GCLK_CLKCTRL_CLKEN)
+	waitForSync()
+
+	// Remove the OnDemand mode, Bug http://avr32.icgroup.norway.atmel.com/bugzilla/show_bug.cgi?id=9905
+	sam.SYSCTRL.DFLLCTRL = sam.SYSCTRL_DFLLCTRL_ENABLE
+	// Wait for ready
+	for (sam.SYSCTRL.PCLKSR & sam.SYSCTRL_PCLKSR_DFLLRDY) == 0 {
+	}
+
+	// Handle DFLL calibration based on info learned from Arduino SAMD implementation,
+	// using default values.
+	sam.SYSCTRL.DFLLVAL |= (0x1f << sam.SYSCTRL_DFLLVAL_COARSE_Pos)
+	sam.SYSCTRL.DFLLVAL |= (0x1ff << sam.SYSCTRL_DFLLVAL_FINE_Pos)
+
+	// Write full configuration to DFLL control register
+	// SYSCTRL_DFLLMUL_CSTEP( 0x1f / 4 ) | // Coarse step is 31, half of the max value
+	// SYSCTRL_DFLLMUL_FSTEP( 10 ) |
+	// SYSCTRL_DFLLMUL_MUL( (48000) ) ;
+	sam.SYSCTRL.DFLLMUL = sam.RegValue((31 << sam.SYSCTRL_DFLLMUL_CSTEP_Pos) |
+		(10 << sam.SYSCTRL_DFLLMUL_FSTEP_Pos) |
+		(48000 << sam.SYSCTRL_DFLLMUL_MUL_Pos))
+
+	// disable DFLL
+	sam.SYSCTRL.DFLLCTRL = 0
+	waitForSync()
+
+	sam.SYSCTRL.DFLLCTRL |= sam.SYSCTRL_DFLLCTRL_MODE |
+		sam.SYSCTRL_DFLLCTRL_CCDIS |
+		sam.SYSCTRL_DFLLCTRL_USBCRM |
+		sam.SYSCTRL_DFLLCTRL_BPLCKC
+	// Wait for ready
+	for (sam.SYSCTRL.PCLKSR & sam.SYSCTRL_PCLKSR_DFLLRDY) == 0 {
+	}
+
+	// Re-enable the DFLL
+	sam.SYSCTRL.DFLLCTRL |= sam.SYSCTRL_DFLLCTRL_ENABLE
+	// Wait for ready
+	for (sam.SYSCTRL.PCLKSR & sam.SYSCTRL_PCLKSR_DFLLRDY) == 0 {
+	}
+
+	// Switch Generic Clock Generator 0 to DFLL48M. CPU will run at 48MHz.
+	sam.GCLK.GENDIV = sam.RegValue((0 << sam.GCLK_GENDIV_ID_Pos) |
+		(0 << sam.GCLK_GENDIV_DIV_Pos))
+	waitForSync()
+
+	sam.GCLK.GENCTRL = sam.RegValue((0 << sam.GCLK_GENCTRL_ID_Pos) |
+		(sam.GCLK_GENCTRL_SRC_DFLL48M << sam.GCLK_GENCTRL_SRC_Pos) |
+		sam.GCLK_GENCTRL_IDC |
+		sam.GCLK_GENCTRL_GENEN)
+	waitForSync()
+
+	// Modify PRESCaler value of OSC8M to have 8MHz
+	sam.SYSCTRL.OSC8M |= (sam.SYSCTRL_OSC8M_PRESC_0 << sam.SYSCTRL_OSC8M_PRESC_Pos)
+	sam.SYSCTRL.OSC8M &^= (1 << sam.SYSCTRL_OSC8M_ONDEMAND_Pos)
+	// Wait for oscillator stabilization
+	for (sam.SYSCTRL.PCLKSR & sam.SYSCTRL_PCLKSR_OSC8MRDY) == 0 {
+	}
+
+	// Use OSC8M as source for Generic Clock Generator 3
+	sam.GCLK.GENDIV = sam.RegValue((3 << sam.GCLK_GENDIV_ID_Pos))
+	waitForSync()
+
+	sam.GCLK.GENCTRL = sam.RegValue((3 << sam.GCLK_GENCTRL_ID_Pos) |
+		(sam.GCLK_GENCTRL_SRC_OSC8M << sam.GCLK_GENCTRL_SRC_Pos) |
+		sam.GCLK_GENCTRL_GENEN)
+	waitForSync()
+
+	// Use OSC32K as source for Generic Clock Generator 2
+	// OSC32K/1 -> GCLK2 at 32KHz
+	sam.GCLK.GENDIV = sam.RegValue(2 << sam.GCLK_GENDIV_ID_Pos)
+	waitForSync()
+
+	sam.GCLK.GENCTRL = sam.RegValue((2 << sam.GCLK_GENCTRL_ID_Pos) |
+		(sam.GCLK_GENCTRL_SRC_OSC32K << sam.GCLK_GENCTRL_SRC_Pos) |
+		sam.GCLK_GENCTRL_GENEN)
+	waitForSync()
+
+	// Use GCLK2 for RTC
+	sam.GCLK.CLKCTRL = sam.RegValue16((sam.GCLK_CLKCTRL_ID_RTC << sam.GCLK_CLKCTRL_ID_Pos) |
+		(sam.GCLK_CLKCTRL_GEN_GCLK2 << sam.GCLK_CLKCTRL_GEN_Pos) |
+		sam.GCLK_CLKCTRL_CLKEN)
+	waitForSync()
+
+	// Set the CPU, APBA, B, and C dividers
+	sam.PM.CPUSEL = sam.PM_CPUSEL_CPUDIV_DIV1
+	sam.PM.APBASEL = sam.PM_APBASEL_APBADIV_DIV1
+	sam.PM.APBBSEL = sam.PM_APBBSEL_APBBDIV_DIV1
+	sam.PM.APBCSEL = sam.PM_APBCSEL_APBCDIV_DIV1
+
+	// Disable automatic NVM write operations
+	sam.NVMCTRL.CTRLB |= sam.NVMCTRL_CTRLB_MANW
+}
+
+func initRTC() {
+	// turn on digital interface clock
+	sam.PM.APBAMASK |= sam.PM_APBAMASK_RTC_
+
+	// disable RTC
+	sam.RTC.MODE0.CTRL = 0
+	waitForSync()
+
+	// reset RTC
+	sam.RTC.MODE0.CTRL |= sam.RTC_MODE0_CTRL_SWRST
+	waitForSync()
+
+	// set Mode0 to 32-bit counter (mode 0) with prescaler 1 and GCLK2 is 32KHz/1
+	sam.RTC.MODE0.CTRL = sam.RegValue16((sam.RTC_MODE0_CTRL_MODE_COUNT32 << sam.RTC_MODE0_CTRL_MODE_Pos) |
+		(sam.RTC_MODE0_CTRL_PRESCALER_DIV1 << sam.RTC_MODE0_CTRL_PRESCALER_Pos) |
+		sam.RTC_MODE0_CTRL_MATCHCLR)
+	waitForSync()
+
+	sam.RTC.MODE0.COMP0 = 0xffffffff
+	waitForSync()
+
+	// re-enable RTC
+	sam.RTC.MODE0.CTRL |= sam.RTC_MODE0_CTRL_ENABLE
+	waitForSync()
+
+	arm.EnableIRQ(sam.IRQ_RTC)
+}
+
+func waitForSync() {
+	for (sam.GCLK.STATUS & sam.GCLK_STATUS_SYNCBUSY) > 0 {
+	}
+}
+
+// treat all ticks params coming from runtime as being in microseconds
+const tickMicros = 1000
+
+var (
+	timestamp        timeUnit // ticks since boottime
+	timerLastCounter uint64
+)
+
+//go:volatile
+type isrFlag bool
+
+var timerWakeup isrFlag
+
+// sleepTicks should sleep for d number of microseconds.
+func sleepTicks(d timeUnit) {
+	for d != 0 {
+		ticks() // update timestamp
+		ticks := uint32(d)
+		timerSleep(ticks)
+		d -= timeUnit(ticks)
+	}
+}
+
+// ticks returns number of microseconds since start.
+func ticks() timeUnit {
+	// request read of count
+	sam.RTC.MODE0.READREQ = sam.RTC_MODE0_READREQ_RREQ
+	waitForSync()
+
+	rtcCounter := uint64(sam.RTC.MODE0.COUNT) * 30 // each counter tick == 30.5us
+	offset := (rtcCounter - timerLastCounter)      // change since last measurement
+	timerLastCounter = rtcCounter
+	timestamp += timeUnit(offset) // TODO: not precise
+	return timestamp
+}
+
+// ticks are in microseconds
+func timerSleep(ticks uint32) {
+	timerWakeup = false
+	if ticks < 30 {
+		// have to have at least one clock count
+		ticks = 30
+	}
+
+	// request read of count
+	sam.RTC.MODE0.READREQ = sam.RTC_MODE0_READREQ_RREQ
+	waitForSync()
+
+	// set compare value
+	cnt := sam.RTC.MODE0.COUNT
+	sam.RTC.MODE0.COMP0 = sam.RegValue(uint32(cnt) + (ticks / 30)) // each counter tick == 30.5us
+	waitForSync()
+
+	// enable IRQ for CMP0 compare
+	sam.RTC.MODE0.INTENSET |= sam.RTC_MODE0_INTENSET_CMP0
+
+	for !timerWakeup {
+		arm.Asm("wfi")
+	}
+}
+
+//go:export RTC_IRQHandler
+func handleRTC() {
+	// disable IRQ for CMP0 compare
+	sam.RTC.MODE0.INTFLAG = sam.RTC_MODE0_INTENSET_CMP0
+
+	timerWakeup = true
+}