machine: make USBCDC global a pointer

Make the USBCDC use a pointer receiver everywhere. This makes it easier
to pass around the object in the future.

This commit sometimes changes code size, but not significantly (a few
bytes) and usually in a positive way.

My eventual goal is the following:

  - Declare `machine.USB` (or similar, name TBD) as a pointer receiver
    for the USB-CDC interface.
  - Let `machine.UART0` always point to an UART, never actually to a
    USBCDC object.
  - Define `machine.Serial`, which is either a real UART or an USB-CDC,
    depending on the board.

This way, if you want a real UART you can use machine.UARTx and if you
just want to print to the default serial port, you can use
machine.Serial.

This change does have an effect on code size and memory consumption.
There is often a small reduction (-8 bytes) in RAM consumption and an
increase in flash consumption.

11 files changed, 64 insertions, 63 deletions

diff --git a/src/machine/board_circuitplay_bluefruit.go b/src/machine/board_circuitplay_bluefruit.go
index 38c3995c1..0a78ca5e8 100644
--- a/src/machine/board_circuitplay_bluefruit.go
+++ b/src/machine/board_circuitplay_bluefruit.go
@@ -58,7 +58,7 @@ const (
 
 // UART0 is the USB device
 var (
-	UART0 = &USB
+	UART0 = USB
 )
 
 // I2C pins
diff --git a/src/machine/board_clue_alpha.go b/src/machine/board_clue_alpha.go
index 0397c4760..a6c8807bf 100644
--- a/src/machine/board_clue_alpha.go
+++ b/src/machine/board_clue_alpha.go
@@ -105,7 +105,7 @@ const (
 
 // UART0 is the USB device
 var (
-	UART0 = &USB
+	UART0 = USB
 )
 
 // I2C pins
diff --git a/src/machine/board_feather-nrf52840.go b/src/machine/board_feather-nrf52840.go
index ae4b54e0f..f353a3b7b 100644
--- a/src/machine/board_feather-nrf52840.go
+++ b/src/machine/board_feather-nrf52840.go
@@ -77,7 +77,7 @@ const (
 
 // UART0 is the USB device
 var (
-	UART0 = &USB
+	UART0 = USB
 )
 
 // I2C pins
diff --git a/src/machine/board_itsybitsy-nrf52840.go b/src/machine/board_itsybitsy-nrf52840.go
index 4d98b669e..e61be0061 100644
--- a/src/machine/board_itsybitsy-nrf52840.go
+++ b/src/machine/board_itsybitsy-nrf52840.go
@@ -72,7 +72,7 @@ const (
 
 // UART0 is the USB device
 var (
-	UART0 = &USB
+	UART0 = USB
 )
 
 // I2C pins
diff --git a/src/machine/board_particle_argon.go b/src/machine/board_particle_argon.go
index 44e5a51ba..5401c4ad9 100644
--- a/src/machine/board_particle_argon.go
+++ b/src/machine/board_particle_argon.go
@@ -41,7 +41,7 @@ const (
 
 // UART
 var (
-	Serial = &USB
+	Serial = USB
 	UART0  = NRF_UART0
 )
 
diff --git a/src/machine/board_particle_boron.go b/src/machine/board_particle_boron.go
index a50d87eb9..cb05e7253 100644
--- a/src/machine/board_particle_boron.go
+++ b/src/machine/board_particle_boron.go
@@ -41,7 +41,7 @@ const (
 
 // UART
 var (
-	Serial = &USB
+	Serial = USB
 	UART0  = NRF_UART0
 )
 
diff --git a/src/machine/board_particle_xenon.go b/src/machine/board_particle_xenon.go
index 7a94cf6d8..c16146364 100644
--- a/src/machine/board_particle_xenon.go
+++ b/src/machine/board_particle_xenon.go
@@ -41,7 +41,7 @@ const (
 
 // UART
 var (
-	Serial = &USB
+	Serial = USB
 	UART0  = NRF_UART0
 )
 
diff --git a/src/machine/machine_atsamd21.go b/src/machine/machine_atsamd21.go
index 4bacd2aab..058099cde 100644
--- a/src/machine/machine_atsamd21.go
+++ b/src/machine/machine_atsamd21.go
@@ -506,7 +506,7 @@ type UART struct {
 
 var (
 	// UART0 is actually a USB CDC interface.
-	UART0 = USBCDC{Buffer: NewRingBuffer()}
+	UART0 = &USBCDC{Buffer: NewRingBuffer()}
 )
 
 const (
@@ -1788,7 +1788,7 @@ func (usbcdc *USBCDC) Flush() error {
 
 			// send data by setting bank ready
 			setEPSTATUSSET(usb_CDC_ENDPOINT_IN, sam.USB_DEVICE_EPSTATUSSET_BK1RDY)
-			UART0.sent = true
+			usbcdc.sent = true
 		}
 	}
 	return nil
@@ -1802,10 +1802,10 @@ func (usbcdc *USBCDC) WriteByte(c byte) error {
 		for {
 			mask := interrupt.Disable()
 
-			idx := UART0.TxIdx.Get()
+			idx := usbcdc.TxIdx.Get()
 			if (idx & usbcdcTxSizeMask) < usbcdcTxSizeMask {
 				udd_ep_in_cache_buffer[usb_CDC_ENDPOINT_IN][idx] = c
-				UART0.TxIdx.Set(idx + 1)
+				usbcdc.TxIdx.Set(idx + 1)
 				ok = true
 			}
 
@@ -1813,26 +1813,26 @@ func (usbcdc *USBCDC) WriteByte(c byte) error {
 
 			if ok {
 				break
-			} else if usbcdcTxMaxRetriesAllowed < UART0.waitTxcRetryCount {
+			} else if usbcdcTxMaxRetriesAllowed < usbcdc.waitTxcRetryCount {
 				mask := interrupt.Disable()
-				UART0.waitTxc = false
-				UART0.waitTxcRetryCount = 0
-				UART0.TxIdx.Set(0)
+				usbcdc.waitTxc = false
+				usbcdc.waitTxcRetryCount = 0
+				usbcdc.TxIdx.Set(0)
 				usbLineInfo.lineState = 0
 				interrupt.Restore(mask)
 				break
 			} else {
 				mask := interrupt.Disable()
-				if UART0.sent {
-					if UART0.waitTxc {
+				if usbcdc.sent {
+					if usbcdc.waitTxc {
 						if (getEPINTFLAG(usb_CDC_ENDPOINT_IN) & sam.USB_DEVICE_EPINTFLAG_TRCPT1) != 0 {
 							setEPSTATUSCLR(usb_CDC_ENDPOINT_IN, sam.USB_DEVICE_EPSTATUSCLR_BK1RDY)
 							setEPINTFLAG(usb_CDC_ENDPOINT_IN, sam.USB_DEVICE_EPINTFLAG_TRCPT1)
-							UART0.waitTxc = false
-							UART0.Flush()
+							usbcdc.waitTxc = false
+							usbcdc.Flush()
 						}
 					} else {
-						UART0.Flush()
+						usbcdc.Flush()
 					}
 				}
 				interrupt.Restore(mask)
@@ -1843,11 +1843,11 @@ func (usbcdc *USBCDC) WriteByte(c byte) error {
 	return nil
 }
 
-func (usbcdc USBCDC) DTR() bool {
+func (usbcdc *USBCDC) DTR() bool {
 	return (usbLineInfo.lineState & usb_CDC_LINESTATE_DTR) > 0
 }
 
-func (usbcdc USBCDC) RTS() bool {
+func (usbcdc *USBCDC) RTS() bool {
 	return (usbLineInfo.lineState & usb_CDC_LINESTATE_RTS) > 0
 }
 
@@ -1882,7 +1882,7 @@ var (
 )
 
 // Configure the USB CDC interface. The config is here for compatibility with the UART interface.
-func (usbcdc USBCDC) Configure(config UARTConfig) {
+func (usbcdc *USBCDC) Configure(config UARTConfig) {
 	// reset USB interface
 	sam.USB_DEVICE.CTRLA.SetBits(sam.USB_DEVICE_CTRLA_SWRST)
 	for sam.USB_DEVICE.SYNCBUSY.HasBits(sam.USB_DEVICE_SYNCBUSY_SWRST) ||
diff --git a/src/machine/machine_atsamd51.go b/src/machine/machine_atsamd51.go
index f8b0a8650..f21d0173d 100644
--- a/src/machine/machine_atsamd51.go
+++ b/src/machine/machine_atsamd51.go
@@ -952,7 +952,7 @@ type UART struct {
 
 var (
 	// UART0 is actually a USB CDC interface.
-	UART0 = USBCDC{Buffer: NewRingBuffer()}
+	UART0 = &USBCDC{Buffer: NewRingBuffer()}
 )
 
 const (
@@ -1994,7 +1994,7 @@ func (usbcdc *USBCDC) Flush() error {
 
 			// send data by setting bank ready
 			setEPSTATUSSET(usb_CDC_ENDPOINT_IN, sam.USB_DEVICE_ENDPOINT_EPSTATUSSET_BK1RDY)
-			UART0.sent = true
+			usbcdc.sent = true
 		}
 	}
 	return nil
@@ -2008,10 +2008,10 @@ func (usbcdc *USBCDC) WriteByte(c byte) error {
 		for {
 			mask := interrupt.Disable()
 
-			idx := UART0.TxIdx.Get()
+			idx := usbcdc.TxIdx.Get()
 			if (idx & usbcdcTxSizeMask) < usbcdcTxSizeMask {
 				udd_ep_in_cache_buffer[usb_CDC_ENDPOINT_IN][idx] = c
-				UART0.TxIdx.Set(idx + 1)
+				usbcdc.TxIdx.Set(idx + 1)
 				ok = true
 			}
 
@@ -2019,26 +2019,26 @@ func (usbcdc *USBCDC) WriteByte(c byte) error {
 
 			if ok {
 				break
-			} else if usbcdcTxMaxRetriesAllowed < UART0.waitTxcRetryCount {
+			} else if usbcdcTxMaxRetriesAllowed < usbcdc.waitTxcRetryCount {
 				mask := interrupt.Disable()
-				UART0.waitTxc = false
-				UART0.waitTxcRetryCount = 0
-				UART0.TxIdx.Set(0)
+				usbcdc.waitTxc = false
+				usbcdc.waitTxcRetryCount = 0
+				usbcdc.TxIdx.Set(0)
 				usbLineInfo.lineState = 0
 				interrupt.Restore(mask)
 				break
 			} else {
 				mask := interrupt.Disable()
-				if UART0.sent {
-					if UART0.waitTxc {
+				if usbcdc.sent {
+					if usbcdc.waitTxc {
 						if (getEPINTFLAG(usb_CDC_ENDPOINT_IN) & sam.USB_DEVICE_ENDPOINT_EPINTFLAG_TRCPT1) != 0 {
 							setEPSTATUSCLR(usb_CDC_ENDPOINT_IN, sam.USB_DEVICE_ENDPOINT_EPSTATUSCLR_BK1RDY)
 							setEPINTFLAG(usb_CDC_ENDPOINT_IN, sam.USB_DEVICE_ENDPOINT_EPINTFLAG_TRCPT1)
-							UART0.waitTxc = false
-							UART0.Flush()
+							usbcdc.waitTxc = false
+							usbcdc.Flush()
 						}
 					} else {
-						UART0.Flush()
+						usbcdc.Flush()
 					}
 				}
 				interrupt.Restore(mask)
@@ -2049,11 +2049,11 @@ func (usbcdc *USBCDC) WriteByte(c byte) error {
 	return nil
 }
 
-func (usbcdc USBCDC) DTR() bool {
+func (usbcdc *USBCDC) DTR() bool {
 	return (usbLineInfo.lineState & usb_CDC_LINESTATE_DTR) > 0
 }
 
-func (usbcdc USBCDC) RTS() bool {
+func (usbcdc *USBCDC) RTS() bool {
 	return (usbLineInfo.lineState & usb_CDC_LINESTATE_RTS) > 0
 }
 
@@ -2088,7 +2088,7 @@ var (
 )
 
 // Configure the USB CDC interface. The config is here for compatibility with the UART interface.
-func (usbcdc USBCDC) Configure(config UARTConfig) {
+func (usbcdc *USBCDC) Configure(config UARTConfig) {
 	// reset USB interface
 	sam.USB_DEVICE.CTRLA.SetBits(sam.USB_DEVICE_CTRLA_SWRST)
 	for sam.USB_DEVICE.SYNCBUSY.HasBits(sam.USB_DEVICE_SYNCBUSY_SWRST) ||
diff --git a/src/machine/machine_nrf52840_usb.go b/src/machine/machine_nrf52840_usb.go
index fa117b1c4..82a44afe6 100644
--- a/src/machine/machine_nrf52840_usb.go
+++ b/src/machine/machine_nrf52840_usb.go
@@ -58,7 +58,7 @@ func (usbcdc *USBCDC) Flush() error {
 				usbcdc.TxIdx.Set(usbcdcTxBank1st)
 			}
 
-			USB.sent = true
+			usbcdc.sent = true
 		}
 	}
 	return nil
@@ -72,10 +72,10 @@ func (usbcdc *USBCDC) WriteByte(c byte) error {
 		for {
 			mask := interrupt.Disable()
 
-			idx := USB.TxIdx.Get()
+			idx := usbcdc.TxIdx.Get()
 			if (idx & usbcdcTxSizeMask) < usbcdcTxSizeMask {
 				udd_ep_in_cache_buffer[usb_CDC_ENDPOINT_IN][idx] = c
-				USB.TxIdx.Set(idx + 1)
+				usbcdc.TxIdx.Set(idx + 1)
 				ok = true
 			}
 
@@ -83,24 +83,24 @@ func (usbcdc *USBCDC) WriteByte(c byte) error {
 
 			if ok {
 				break
-			} else if usbcdcTxMaxRetriesAllowed < USB.waitTxcRetryCount {
+			} else if usbcdcTxMaxRetriesAllowed < usbcdc.waitTxcRetryCount {
 				mask := interrupt.Disable()
-				USB.waitTxc = false
-				USB.waitTxcRetryCount = 0
-				USB.TxIdx.Set(0)
+				usbcdc.waitTxc = false
+				usbcdc.waitTxcRetryCount = 0
+				usbcdc.TxIdx.Set(0)
 				usbLineInfo.lineState = 0
 				interrupt.Restore(mask)
 				break
 			} else {
 				mask := interrupt.Disable()
-				if USB.sent {
-					if USB.waitTxc {
+				if usbcdc.sent {
+					if usbcdc.waitTxc {
 						if !easyDMABusy.HasBits(1) {
-							USB.waitTxc = false
-							USB.Flush()
+							usbcdc.waitTxc = false
+							usbcdc.Flush()
 						}
 					} else {
-						USB.Flush()
+						usbcdc.Flush()
 					}
 				}
 				interrupt.Restore(mask)
@@ -111,16 +111,17 @@ func (usbcdc *USBCDC) WriteByte(c byte) error {
 	return nil
 }
 
-func (usbcdc USBCDC) DTR() bool {
+func (usbcdc *USBCDC) DTR() bool {
 	return (usbLineInfo.lineState & usb_CDC_LINESTATE_DTR) > 0
 }
 
-func (usbcdc USBCDC) RTS() bool {
+func (usbcdc *USBCDC) RTS() bool {
 	return (usbLineInfo.lineState & usb_CDC_LINESTATE_RTS) > 0
 }
 
 var (
-	USB = USBCDC{Buffer: NewRingBuffer()}
+	USB  = &_USB
+	_USB = USBCDC{Buffer: NewRingBuffer()}
 
 	usbEndpointDescriptors [8]usbDeviceDescriptor
 
@@ -174,7 +175,7 @@ func (usbcdc *USBCDC) Configure(config UARTConfig) {
 	// that it is possible to print to the console from a BLE interrupt. You
 	// shouldn't generally do that but it is useful for debugging and panic
 	// logging.
-	usbcdc.interrupt = interrupt.New(nrf.IRQ_USBD, USB.handleInterrupt)
+	usbcdc.interrupt = interrupt.New(nrf.IRQ_USBD, _USB.handleInterrupt)
 	usbcdc.interrupt.SetPriority(0x40) // interrupt priority 2 (lower number means more important)
 	usbcdc.interrupt.Enable()
 
@@ -198,7 +199,7 @@ func (usbcdc *USBCDC) Configure(config UARTConfig) {
 func (usbcdc *USBCDC) handleInterrupt(interrupt.Interrupt) {
 	if nrf.USBD.EVENTS_SOF.Get() == 1 {
 		nrf.USBD.EVENTS_SOF.Set(0)
-		USB.Flush()
+		usbcdc.Flush()
 		// if you want to blink LED showing traffic, this would be the place...
 	}
 
@@ -292,7 +293,7 @@ func (usbcdc *USBCDC) handleInterrupt(interrupt.Interrupt) {
 					}
 				case usb_CDC_ENDPOINT_IN: //, usb_CDC_ENDPOINT_ACM:
 					if inDataDone {
-						USB.waitTxc = false
+						usbcdc.waitTxc = false
 						exitCriticalSection()
 					}
 				}
@@ -496,7 +497,7 @@ func sendUSBPacket(ep uint32, data []byte) {
 	)
 }
 
-func (usbcdc USBCDC) handleEndpoint(ep uint32) {
+func (usbcdc *USBCDC) handleEndpoint(ep uint32) {
 	// get data
 	count := int(nrf.USBD.EPOUT[ep].AMOUNT.Get())
 
diff --git a/src/machine/usb.go b/src/machine/usb.go
index 0b5470060..4bea1880d 100644
--- a/src/machine/usb.go
+++ b/src/machine/usb.go
@@ -604,7 +604,7 @@ func newUSBSetup(data []byte) usbSetup {
 //
 
 // Read from the RX buffer.
-func (usbcdc USBCDC) Read(data []byte) (n int, err error) {
+func (usbcdc *USBCDC) Read(data []byte) (n int, err error) {
 	// check if RX buffer is empty
 	size := usbcdc.Buffered()
 	if size == 0 {
@@ -626,7 +626,7 @@ func (usbcdc USBCDC) Read(data []byte) (n int, err error) {
 }
 
 // Write data to the USBCDC.
-func (usbcdc USBCDC) Write(data []byte) (n int, err error) {
+func (usbcdc *USBCDC) Write(data []byte) (n int, err error) {
 	for _, v := range data {
 		usbcdc.WriteByte(v)
 	}
@@ -635,7 +635,7 @@ func (usbcdc USBCDC) Write(data []byte) (n int, err error) {
 
 // ReadByte reads a single byte from the RX buffer.
 // If there is no data in the buffer, returns an error.
-func (usbcdc USBCDC) ReadByte() (byte, error) {
+func (usbcdc *USBCDC) ReadByte() (byte, error) {
 	// check if RX buffer is empty
 	buf, ok := usbcdc.Buffer.Get()
 	if !ok {
@@ -645,13 +645,13 @@ func (usbcdc USBCDC) ReadByte() (byte, error) {
 }
 
 // Buffered returns the number of bytes currently stored in the RX buffer.
-func (usbcdc USBCDC) Buffered() int {
+func (usbcdc *USBCDC) Buffered() int {
 	return int(usbcdc.Buffer.Used())
 }
 
 // Receive handles adding data to the UART's data buffer.
 // Usually called by the IRQ handler for a machine.
-func (usbcdc USBCDC) Receive(data byte) {
+func (usbcdc *USBCDC) Receive(data byte) {
 	usbcdc.Buffer.Put(data)
 }