nrf52840: implement USB-CDC (#883)

* machine/nrf52840: usb-cdc implementation

Author: syoder

src/machine/board_circuitplay_bluefruit.go

@@ -56,6 +56,11 @@ const (
 	UART_RX_PIN = P0_30 // PORTB
 )
 
+// UART0 is the USB device
+var (
+	UART0 = USB
+)
+
 // I2C pins
 const (
 	SDA_PIN = P0_05 // I2C0 external

src/machine/board_clue_alpha.go

@@ -103,6 +103,11 @@ const (
 	UART_TX_PIN = D1
 )
 
+// UART0 is the USB device
+var (
+	UART0 = USB
+)
+
 // I2C pins
 const (
 	SDA_PIN = D20 // I2C0 external

src/machine/board_nrf52840-mdk.go

@@ -18,6 +18,11 @@ const (
 	UART_RX_PIN Pin = 19
 )
 
+// UART0 is the USB device
+var (
+	UART0 = USB
+)
+
 // I2C pins (unused)
 const (
 	SDA_PIN = NoPin

src/machine/board_pca10056_baremetal.go

@@ -0,0 +1,8 @@
+// +build nrf52840,pca10056
+
+package machine
+
+// UART0 is the NRF UART
+var (
+	UART0 = NRF_UART0
+)

src/machine/board_reelboard_baremetal.go

@@ -0,0 +1,8 @@
+// +build nrf52840,reelboard
+
+package machine
+
+// UART0 is the NRF UART
+var (
+	UART0 = NRF_UART0
+)

src/machine/machine_nrf.go

@@ -66,8 +66,8 @@ type UART struct {
 
 // UART
 var (
-	// UART0 is the hardware serial port on the NRF.
-	UART0 = UART{Buffer: NewRingBuffer()}
+	// NRF_UART0 is the hardware UART on the NRF SoC.
+	NRF_UART0 = UART{Buffer: NewRingBuffer()}
 )
 
 // Configure the UART.
@@ -88,7 +88,7 @@ func (uart UART) Configure(config UARTConfig) {
 	nrf.UART0.INTENSET.Set(nrf.UART_INTENSET_RXDRDY_Msk)
 
 	// Enable RX IRQ.
-	intr := interrupt.New(nrf.IRQ_UART0, UART0.handleInterrupt)
+	intr := interrupt.New(nrf.IRQ_UART0, NRF_UART0.handleInterrupt)
 	intr.SetPriority(0xc0) // low priority
 	intr.Enable()
 }

src/machine/machine_nrf51.go

@@ -6,6 +6,10 @@ import (
 	"device/nrf"
 )
 
+var (
+	UART0 = NRF_UART0
+)
+
 func CPUFrequency() uint32 {
 	return 16000000
 }

src/machine/machine_nrf52.go

@@ -7,6 +7,10 @@ import (
 	"unsafe"
 )
 
+var (
+	UART0 = NRF_UART0
+)
+
 func CPUFrequency() uint32 {
 	return 64000000
 }

src/machine/usb.go

@@ -1,4 +1,4 @@
-// +build sam
+// +build sam nrf52840
 
 package machine
 
@@ -376,6 +376,23 @@ type cdcLineInfo struct {
 	lineState   uint8
 }
 
+// strToUTF16LEDescriptor converts a utf8 string into a string descriptor
+// note: the following code only converts ascii characters to UTF16LE. In order
+// to do a "proper" conversion, we would need to pull in the 'unicode/utf16'
+// package, which at the time this was written added 512 bytes to the compiled
+// binary.
+func strToUTF16LEDescriptor(in string) []byte {
+	size := (len(in) << 1) + 2
+	out := make([]byte, size)
+	out[0] = byte(size)
+	out[1] = 0x03
+	for i, rune := range in {
+		out[(i<<1)+2] = byte(rune)
+		out[(i<<1)+3] = 0
+	}
+	return out
+}
+
 var (
 	// TODO: allow setting these
 	usb_STRING_LANGUAGE     = [2]uint16{(3 << 8) | (2 + 2), 0x0409} // English