mirror of
https://github.com/tinygo-org/drivers.git
synced 2026-08-07 16:33:39 +00:00
Ayke van Laethem
91539d9ef8
Avoid creating unnecessary garbage in the following ways:
* Use the Transfer method instead of the Tx method for single byte
transfers.
* Use a statically allocated buffer for the fixed start-of-frame
sequence.
Running this for a few minutes did not cause the garbage collector to
run. Previously, it would run every second or so in a
persistence-of-vision application.
71 lines
1.7 KiB
Go
71 lines
1.7 KiB
Go
package apa102
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import "machine"
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// bbSPI is a dumb bit-bang implementation of SPI protocol that is hardcoded
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// to mode 0 and ignores trying to receive data. Just enough for the APA102.
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// Note: making this unexported for now because it is probable not suitable
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// most purposes other than the APA102 package. It might be desirable to make
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// this more generic and include it in the TinyGo "machine" package instead.
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type bbSPI struct {
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SCK machine.Pin
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MOSI machine.Pin
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Delay uint32
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}
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// Configure sets up the SCK and MOSI pins as outputs and sets them low
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func (s *bbSPI) Configure() {
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s.SCK.Configure(machine.PinConfig{Mode: machine.PinOutput})
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s.MOSI.Configure(machine.PinConfig{Mode: machine.PinOutput})
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s.SCK.Low()
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s.MOSI.Low()
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if s.Delay == 0 {
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s.Delay = 1
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}
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}
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// Tx matches signature of machine.SPI.Tx() and is used to send multiple bytes.
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// The r slice is ignored and no error will ever be returned.
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func (s *bbSPI) Tx(w []byte, r []byte) error {
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s.Configure()
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for _, b := range w {
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s.Transfer(b)
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}
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return nil
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}
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// delay represents a quarter of the clock cycle
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func (s *bbSPI) delay() {
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for i := uint32(0); i < s.Delay; {
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i++
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}
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}
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// Transfer matches signature of machine.SPI.Transfer() and is used to send a
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// single byte. The received data is ignored and no error will ever be returned.
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func (s *bbSPI) Transfer(b byte) (byte, error) {
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for i := uint8(0); i < 8; i++ {
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// half clock cycle high to start
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s.SCK.High()
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s.delay()
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// write the value to MOSI (MSB first)
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if b&(1<<(7-i)) == 0 {
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s.MOSI.Low()
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} else {
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s.MOSI.High()
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}
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s.delay()
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// half clock cycle low
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s.SCK.Low()
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s.delay()
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// for actual SPI would try to read the MISO value here
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s.delay()
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}
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return 0, nil
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}
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