machine: add KHz, MHz, GHz constants, deprecate TWI_FREQ_* constants

There are two main issues with these constants:

  * They don't follow the Go naming convention.
  * They call themselves "TWI", while it makes a lot more sense to refer
    to the actual name which is I2C (or I²C).

I have not removed them but just deprecated them. Perhaps we can remove
them when we move towards version 1.0.

src/machine/i2c.go

@@ -8,6 +8,8 @@ import (
 )
 
 // TWI_FREQ is the I2C bus speed. Normally either 100 kHz, or 400 kHz for high-speed bus.
+//
+// Deprecated: use 100 * machine.KHz or 400 * machine.KHz instead.
 const (
 	TWI_FREQ_100KHZ = 100000
 	TWI_FREQ_400KHZ = 400000

src/machine/machine.go

@@ -18,6 +18,13 @@ var (
 // particular chip but instead runs in WebAssembly for example.
 const Device = deviceName
 
+// Generic constants.
+const (
+	KHz = 1000
+	MHz = 1000_000
+	GHz = 1000_000_000
+)
+
 // PinMode sets the direction and pull mode of the pin. For example, PinOutput
 // sets the pin as an output and PinInputPullup sets the pin as an input with a
 // pull-up.

src/machine/machine_atmega.go

@@ -26,7 +26,7 @@ type I2CConfig struct {
 func (i2c *I2C) Configure(config I2CConfig) error {
 	// Default I2C bus speed is 100 kHz.
 	if config.Frequency == 0 {
-		config.Frequency = TWI_FREQ_100KHZ
+		config.Frequency = 100 * KHz
 	}
 
 	// Activate internal pullups for twi.

src/machine/machine_atsamd21.go

@@ -677,7 +677,7 @@ const i2cTimeout = 1000
 func (i2c *I2C) Configure(config I2CConfig) error {
 	// Default I2C bus speed is 100 kHz.
 	if config.Frequency == 0 {
-		config.Frequency = TWI_FREQ_100KHZ
+		config.Frequency = 100 * KHz
 	}
 	if config.SDA == 0 && config.SCL == 0 {
 		config.SDA = SDA_PIN

src/machine/machine_atsamd51.go

@@ -1151,7 +1151,7 @@ const i2cTimeout = 1000
 func (i2c *I2C) Configure(config I2CConfig) error {
 	// Default I2C bus speed is 100 kHz.
 	if config.Frequency == 0 {
-		config.Frequency = TWI_FREQ_100KHZ
+		config.Frequency = 100 * KHz
 	}
 
 	// Use default I2C pins if not set.

src/machine/machine_fe310.go

@@ -231,7 +231,7 @@ type I2CConfig struct {
 func (i2c *I2C) Configure(config I2CConfig) error {
 	var i2cClockFrequency uint32 = 32000000
 	if config.Frequency == 0 {
-		config.Frequency = TWI_FREQ_100KHZ
+		config.Frequency = 100 * KHz
 	}
 
 	if config.SDA == 0 && config.SCL == 0 {

src/machine/machine_k210.go

@@ -523,7 +523,7 @@ type I2CConfig struct {
 func (i2c *I2C) Configure(config I2CConfig) error {
 
 	if config.Frequency == 0 {
-		config.Frequency = TWI_FREQ_100KHZ
+		config.Frequency = 100 * KHz
 	}
 
 	if config.SDA == 0 && config.SCL == 0 {

src/machine/machine_mimxrt1062_i2c.go

@@ -10,15 +10,6 @@ import (
 	"errors"
 )
 
-const (
-	TWI_FREQ_BUS     = 24000000        // LPI2C root clock is on 24 MHz OSC
-	TWI_FREQ_100KHZ  = 100000          // StandardMode (100 kHz)
-	TWI_FREQ_400KHZ  = 400000          // FastMode (400 kHz)
-	TWI_FREQ_1MHZ    = 1000000         // FastModePlus (1 MHz)
-	TWI_FREQ_5MHZ    = 5000000         // UltraFastMode (5 MHz)
-	TWI_FREQ_DEFAULT = TWI_FREQ_100KHZ // default to StandardMode (100 kHz)
-)
-
 var (
 	errI2CWriteTimeout       = errors.New("I2C timeout during write")
 	errI2CReadTimeout        = errors.New("I2C timeout during read")
@@ -174,7 +165,7 @@ func (i2c *I2C) Configure(config I2CConfig) {
 
 	freq := config.Frequency
 	if 0 == freq {
-		freq = TWI_FREQ_DEFAULT
+		freq = 100 * KHz
 	}
 
 	// reset clock and registers, and enable LPI2C module interface
@@ -305,7 +296,7 @@ func (i2c *I2C) setFrequency(freq uint32) {
 	wasEnabled := i2c.Bus.MCR.HasBits(nxp.LPI2C_MCR_MEN)
 	i2c.Bus.MCR.ClearBits(nxp.LPI2C_MCR_MEN)
 
-	// baud rate = (TWI_FREQ_BUS/(2^pre))/(CLKLO+1 + CLKHI+1 + FLOOR((2+FILTSCL)/(2^pre)))
+	// baud rate = (24MHz/(2^pre))/(CLKLO+1 + CLKHI+1 + FLOOR((2+FILTSCL)/(2^pre)))
 	// assume: CLKLO=2*CLKHI, SETHOLD=CLKHI, DATAVD=CLKHI/2
 	for pre := uint32(1); pre <= 128; pre *= 2 {
 		if bestError == 0 {
@@ -314,9 +305,9 @@ func (i2c *I2C) setFrequency(freq uint32) {
 		for clkHi := uint32(1); clkHi < 32; clkHi++ {
 			var absError, rate uint32
 			if clkHi == 1 {
-				rate = (TWI_FREQ_BUS / pre) / (1 + 3 + 2 + 2/pre)
+				rate = (24 * MHz / pre) / (1 + 3 + 2 + 2/pre)
 			} else {
-				rate = (TWI_FREQ_BUS / pre) / (3*clkHi + 2 + 2/pre)
+				rate = (24 * MHz / pre) / (3*clkHi + 2 + 2/pre)
 			}
 			if freq > rate {
 				absError = freq - rate
@@ -370,15 +361,15 @@ func (i2c *I2C) setFrequency(freq uint32) {
 		mcfgr2, mcfgr3 uint32
 	)
 	const i2cClockStretchTimeout = 15000 // microseconds
-	if freq >= TWI_FREQ_5MHZ {
+	if freq >= 5*MHz {
 		// I2C UltraFastMode 5 MHz
 		mcfgr2 = 0 // disable glitch filters and timeout for UltraFastMode
 		mcfgr3 = 0 //
-	} else if freq >= TWI_FREQ_1MHZ {
+	} else if freq >= 1*MHz {
 		// I2C FastModePlus 1 MHz
 		mcfgr2 = filtsda(1) | filtscl(1) | busidle(2400) // 100us timeout
 		mcfgr3 = pinlow(i2cClockStretchTimeout*24/256 + 1)
-	} else if freq >= TWI_FREQ_400KHZ {
+	} else if freq >= 400*KHz {
 		// I2C FastMode 400 kHz
 		mcfgr2 = filtsda(2) | filtscl(2) | busidle(3600) // 150us timeout
 		mcfgr3 = pinlow(i2cClockStretchTimeout*24/256 + 1)

src/machine/machine_nrf.go

@@ -230,7 +230,7 @@ func (i2c *I2C) Configure(config I2CConfig) error {
 
 	// Default I2C bus speed is 100 kHz.
 	if config.Frequency == 0 {
-		config.Frequency = TWI_FREQ_100KHZ
+		config.Frequency = 100 * KHz
 	}
 	// Default I2C pins if not set.
 	if config.SDA == 0 && config.SCL == 0 {
@@ -253,7 +253,7 @@ func (i2c *I2C) Configure(config I2CConfig) error {
 		(nrf.GPIO_PIN_CNF_DRIVE_S0D1 << nrf.GPIO_PIN_CNF_DRIVE_Pos) |
 		(nrf.GPIO_PIN_CNF_SENSE_Disabled << nrf.GPIO_PIN_CNF_SENSE_Pos))
 
-	if config.Frequency == TWI_FREQ_400KHZ {
+	if config.Frequency >= 400*KHz {
 		i2c.Bus.FREQUENCY.Set(nrf.TWI_FREQUENCY_FREQUENCY_K400)
 	} else {
 		i2c.Bus.FREQUENCY.Set(nrf.TWI_FREQUENCY_FREQUENCY_K100)

src/machine/machine_rp2040_clocks.go

@@ -10,11 +10,6 @@ import (
 	"unsafe"
 )
 
-const (
-	KHz = 1000
-	MHz = 1000000
-)
-
 func CPUFrequency() uint32 {
 	return 125 * MHz
 }

src/machine/machine_stm32_i2c_reva.go

@@ -137,7 +137,7 @@ func (i2c *I2C) Configure(config I2CConfig) error {
 
 	// default to 100 kHz (Sm, standard mode) if no frequency is set
 	if config.Frequency == 0 {
-		config.Frequency = TWI_FREQ_100KHZ
+		config.Frequency = 100 * KHz
 	}
 
 	// configure I2C input clock