mirror of
https://github.com/tinygo-org/tinygo.git
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sago35
132 lines
2.2 KiB
Go
132 lines
2.2 KiB
Go
package usb
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import (
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"errors"
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"runtime/volatile"
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)
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const QueueSize = 8
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type Queue struct {
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fifo [QueueSize]uint8
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tail volatile.Register32
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head volatile.Register32
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}
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var (
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ErrReadBuffer = errors.New("cannot copy into read buffer")
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ErrWriteBuffer = errors.New("cannot copy from write buffer")
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ErrQueueEmpty = errors.New("data queue empty") // Read Error
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ErrQueueFull = errors.New("data queue full") // Write error
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)
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// Reset discards all buffered data.
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//go:inline
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func (q *Queue) Reset() {
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for i := range q.fifo {
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q.fifo[i] = 0
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}
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q.tail.Set(0)
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q.head.Set(0)
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}
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//go:inline
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func (q *Queue) Len() int {
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return int(q.tail.Get() - q.head.Get())
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}
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//go:inline
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func (q *Queue) Cap() int {
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return cap(q.fifo)
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}
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func (q *Queue) Read(data []uint8) (int, error) {
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less := uint32(len(data))
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if less == 0 {
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return 0, ErrReadBuffer
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} // nothing to copy into
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head := q.head.Get()
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used := q.tail.Get() - head
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if used == 0 {
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return 0, ErrQueueEmpty
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} // empty queue
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if less > used {
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less = used
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} // only get from used space
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for i := uint32(0); i < less; i++ {
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data[i] = q.fifo[head%QueueSize]
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head++
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}
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q.head.Set(head)
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return int(less), nil
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}
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func (q *Queue) Write(data []uint8) (int, error) {
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more := uint32(len(data))
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if more == 0 {
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return 0, ErrWriteBuffer
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} // nothing to copy from
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tail := q.tail.Get()
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used := tail - q.head.Get()
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if used == QueueSize {
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return 0, ErrQueueFull
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} // full queue
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if used+more > QueueSize {
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more = QueueSize - used
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} // only put to unused space
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for i := uint32(0); i < more; i++ {
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q.fifo[tail%QueueSize] = data[i]
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tail++
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}
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q.tail.Set(tail)
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return int(more), nil
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}
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func (q *Queue) Deq() (uint8, bool) {
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tail := q.head.Get()
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if tail == q.tail.Get() {
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return 0, false
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} // empty queue
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data := q.fifo[tail%QueueSize]
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q.head.Set(tail + 1)
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return data, true
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}
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func (q *Queue) Front() (uint8, bool) {
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tail := q.head.Get()
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if tail == q.tail.Get() {
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return 0, false
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} // empty queue
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return q.fifo[tail%QueueSize], true
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}
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func (q *Queue) Enq(data uint8) bool {
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head := q.tail.Get()
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if head-q.head.Get() == QueueSize {
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return false
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} // full queue
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q.fifo[head%QueueSize] = data
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q.tail.Set(head + 1)
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return true
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}
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