samd21,samd51,nrf52840: add support for USBHID (keyboard / mouse)

src/machine/usb/hid/buffer.go

@@ -0,0 +1,52 @@
+package hid
+
+import (
+	"runtime/volatile"
+)
+
+const bufferSize = 128
+
+// RingBuffer is ring buffer implementation inspired by post at
+// https://www.embeddedrelated.com/showthread/comp.arch.embedded/77084-1.php
+type RingBuffer struct {
+	rxbuffer [bufferSize][9]byte
+	head     volatile.Register8
+	tail     volatile.Register8
+}
+
+// NewRingBuffer returns a new ring buffer.
+func NewRingBuffer() *RingBuffer {
+	return &RingBuffer{}
+}
+
+// Used returns how many bytes in buffer have been used.
+func (rb *RingBuffer) Used() uint8 {
+	return uint8(rb.head.Get() - rb.tail.Get())
+}
+
+// Put stores a byte in the buffer. If the buffer is already
+// full, the method will return false.
+func (rb *RingBuffer) Put(val []byte) bool {
+	if rb.Used() != bufferSize {
+		rb.head.Set(rb.head.Get() + 1)
+		copy(rb.rxbuffer[rb.head.Get()%bufferSize][:], val)
+		return true
+	}
+	return false
+}
+
+// Get returns a byte from the buffer. If the buffer is empty,
+// the method will return a false as the second value.
+func (rb *RingBuffer) Get() ([]byte, bool) {
+	if rb.Used() != 0 {
+		rb.tail.Set(rb.tail.Get() + 1)
+		return rb.rxbuffer[rb.tail.Get()%bufferSize][:], true
+	}
+	return nil, false
+}
+
+// Clear resets the head and tail pointer to zero.
+func (rb *RingBuffer) Clear() {
+	rb.head.Set(0)
+	rb.tail.Set(0)
+}