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Feat/nrf52xxx/spi/improve #4699

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Feat/nrf52xxx/spi/improve #4699

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34bb9e8
feat(src/machine/nrf52xxx/spi): add mode
milkpirate Jan 14, 2025
5c202bd
feat(src/machine/nrf52xxx/spi): re-use case instead of dedicated
milkpirate Jan 14, 2025
08b2d01
feat(src/machine/nrf52xxx/spi): implement io.Reader, io.Writer
milkpirate Jan 14, 2025
e8aa554
chore(dependencies): remove residuals
milkpirate Jan 14, 2025
6163664
chore(review): honor
milkpirate Jan 18, 2025
7f95f43
Merge branch 'dev' into feat/nrf52xxx/spi/improve
milkpirate Jan 20, 2025
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75 changes: 47 additions & 28 deletions src/machine/machine_nrf52xxx.go
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Original file line number Diff line number Diff line change
Expand Up @@ -8,6 +8,27 @@ import (
"unsafe"
)

const (
SPI_MODE_CPHA0_CPOL0 SPIMode = iota
SPI_MODE_CPHA1_CPOL0
SPI_MODE_CPHA1_CPOL1
SPI_MODE_CPHA0_CPOL1

SPI_MODE_CPHA_FALLING_EDGE_CPOL_ACTIVE_LOW = SPI_MODE_CPHA0_CPOL0
SPI_MODE_CPHA_RISING_EDGE_CPOL_ACTIVE_LOW = SPI_MODE_CPHA1_CPOL0
SPI_MODE_CPHA_RISING_EDGE_CPOL_ACTIVE_HIGH = SPI_MODE_CPHA1_CPOL1
SPI_MODE_CPHA_FALLING_EDGE_CPOL_ACTIVE_HIGH = SPI_MODE_CPHA0_CPOL1
)

// There are 3 SPI interfaces on the NRF528xx.
var (
SPI0 = SPI{Bus: nrf.SPIM0}
SPI1 = SPI{Bus: nrf.SPIM1}
SPI2 = SPI{Bus: nrf.SPIM2}
)

type SPIMode uint8
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func CPUFrequency() uint32 {
return 64000000
}
Expand Down Expand Up @@ -189,16 +210,8 @@ func (a *ADC) Get() uint16 {
// SPI on the NRF.
type SPI struct {
Bus *nrf.SPIM_Type
buf *[1]byte // 1-byte buffer for the Transfer method
}

// There are 3 SPI interfaces on the NRF528xx.
var (
SPI0 = SPI{Bus: nrf.SPIM0, buf: new([1]byte)}
SPI1 = SPI{Bus: nrf.SPIM1, buf: new([1]byte)}
SPI2 = SPI{Bus: nrf.SPIM2, buf: new([1]byte)}
)

// SPIConfig is used to store config info for SPI.
type SPIConfig struct {
Frequency uint32
Expand All @@ -210,18 +223,15 @@ type SPIConfig struct {
}

// Configure is intended to set up the SPI interface.
func (spi SPI) Configure(config SPIConfig) error {
func (spi *SPI) Configure(config SPIConfig) error {
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// Disable bus to configure it
spi.Bus.ENABLE.Set(nrf.SPIM_ENABLE_ENABLE_Disabled)

// Pick a default frequency.
if config.Frequency == 0 {
config.Frequency = 4000000 // 4MHz
}

// set frequency
var freq uint32
switch {
case config.Frequency == 0: // default MCU SPI speed
freq = nrf.SPIM_FREQUENCY_FREQUENCY_M4
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@ysoldak ysoldak Jan 17, 2025 •
edited
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I don't see this as improvement :( Previous code looks cleaner to me: separates concerns of a) ensuring default value and b) handling frequency.

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Found the separate if-statement superfluous, since we already have a flow control on the frequency.

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can you two @ysoldak, @b0ch3nski agree on that?

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I find switch statements much easier to read but I think it's just a matter of personal preference. Nevertheless, we already have a switch here and that lonely if statement looks like it has rejoined it's people 😃

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I find switch statements much easier to read but I think it's just a matter of personal preference. Nevertheless, we already have a switch here and that lonely if statement looks like it has rejoined it's people 😃

Yes, felt the same to me.

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Regarding switch, I must confess, I was struggling to understand what's going on at first.
I was expecting every 'case' to produce a unique value (number of unique values = number of cases in switch).
I would propose merge two cases, but then case condition becomes long and look ugly.

So I still prefer deal with default value first, then handle the value, regardless default it is or not.
It may look nice/smart to have only one switch without an extra "if" before it, because we can, but I'd say readability suffers, at least in my case.

case config.Frequency >= 8000000:
freq = nrf.SPIM_FREQUENCY_FREQUENCY_M8
case config.Frequency >= 4000000:
Expand All @@ -246,24 +256,24 @@ func (spi SPI) Configure(config SPIConfig) error {
conf = (nrf.SPIM_CONFIG_ORDER_LsbFirst << nrf.SPIM_CONFIG_ORDER_Pos)
}

// set mode
switch config.Mode {
case 0:
// set mode, see:
// - https://de.wikipedia.org/wiki/Serial_Peripheral_Interface#/media/Datei:SPI_timing_diagram2.svg
// - https://docs-be.nordicsemi.com/bundle/ps_nrf52840/attach/nRF52840_PS_v1.11.pdf?_LANG=enus page 716, table 43
switch SPIMode(config.Mode) {
case SPI_MODE_CPHA0_CPOL0:
conf &^= (nrf.SPIM_CONFIG_CPOL_ActiveHigh << nrf.SPIM_CONFIG_CPOL_Pos)
conf &^= (nrf.SPIM_CONFIG_CPHA_Leading << nrf.SPIM_CONFIG_CPHA_Pos)
case 1:
case SPI_MODE_CPHA1_CPOL0:
conf &^= (nrf.SPIM_CONFIG_CPOL_ActiveHigh << nrf.SPIM_CONFIG_CPOL_Pos)
conf |= (nrf.SPIM_CONFIG_CPHA_Trailing << nrf.SPIM_CONFIG_CPHA_Pos)
case 2:
case SPI_MODE_CPHA1_CPOL1:
conf |= (nrf.SPIM_CONFIG_CPOL_ActiveLow << nrf.SPIM_CONFIG_CPOL_Pos)
conf &^= (nrf.SPIM_CONFIG_CPHA_Leading << nrf.SPIM_CONFIG_CPHA_Pos)
case 3:
case SPI_MODE_CPHA0_CPOL1:
conf |= (nrf.SPIM_CONFIG_CPOL_ActiveLow << nrf.SPIM_CONFIG_CPOL_Pos)
conf |= (nrf.SPIM_CONFIG_CPHA_Trailing << nrf.SPIM_CONFIG_CPHA_Pos)
default: // to mode
conf &^= (nrf.SPIM_CONFIG_CPOL_ActiveHigh << nrf.SPIM_CONFIG_CPOL_Pos)
conf &^= (nrf.SPIM_CONFIG_CPHA_Leading << nrf.SPIM_CONFIG_CPHA_Pos)
}

spi.Bus.CONFIG.Set(conf)

// set pins
Expand All @@ -283,10 +293,9 @@ func (spi SPI) Configure(config SPIConfig) error {
}

// Transfer writes/reads a single byte using the SPI interface.
func (spi SPI) Transfer(w byte) (byte, error) {
buf := spi.buf[:]
buf[0] = w
err := spi.Tx(buf[:], buf[:])
func (spi *SPI) Transfer(w byte) (byte, error) {
buf := []byte{w}
err := spi.Tx(buf, buf)
return buf[0], err
}

Expand All @@ -295,7 +304,7 @@ func (spi SPI) Transfer(w byte) (byte, error) {
// as bytes read. Therefore, if the number of bytes don't match it will be
// padded until they fit: if len(w) > len(r) the extra bytes received will be
// dropped and if len(w) < len(r) extra 0 bytes will be sent.
func (spi SPI) Tx(w, r []byte) error {
func (spi *SPI) Tx(w, r []byte) error {
// Unfortunately the hardware (on the nrf52832) only supports up to 255
// bytes in the buffers, so if either w or r is longer than that the
// transfer needs to be broken up in pieces.
Expand Down Expand Up @@ -337,6 +346,16 @@ func (spi SPI) Tx(w, r []byte) error {
return nil
}

// Read implements [io.Reader]. And reads as many bytes as the given buffer is long
func (spi *SPI) Read(r []byte) (int, error) {
return len(r), spi.Tx(nil, r)
}

// Write implements [io.Writer]. And writes as long as there are bytes in w.
func (spi *SPI) Write(w []byte) (int, error) {
return len(w), spi.Tx(w, nil)
}

Comment on lines +349 to +358
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Read and Write are not part of the SPI interface. It is easy enough to implement an abstraction if needed that works for all SPI hardwares of all MCUs

func writeSPI(w []byte, spi interface {Tx(w,r []byte) error}) (int,error) {
    return len(w), spi.Tx(w,nil)
}

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@milkpirate milkpirate Jan 18, 2025 •
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Yeah, lets do it! Actually I was surprised that SPI is not supplying it, since it would have seemed the more natural way to interface with SPI than the current one. Can you point me to the relevant file/code section?

// PWM is one PWM peripheral, which consists of a counter and multiple output
// channels (that can be connected to actual pins). You can set the frequency
// using SetPeriod, but only for all the channels in this PWM peripheral at
Expand Down
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