si5351: add support for si5351 (#810)

* si5351: add support for si5351

Adds support for the si5351 I2C programmable clock generator using code
from @chiefMarlin which used code from @conotto which somehow never got merged.

Thank you everyone!

Signed-off-by: deadprogram <ron@hybridgroup.com>

* refactor: use regmap instead of legacy package to avoid heap allocations

Signed-off-by: deadprogram <ron@hybridgroup.com>

---------

Signed-off-by: deadprogram <ron@hybridgroup.com>

examples/si5351/main.go

@@ -0,0 +1,107 @@
+package main
+
+import (
+	"machine"
+	"time"
+
+	"tinygo.org/x/drivers/si5351"
+)
+
+// Simple demo of the SI5351 clock generator.
+// This is like the Arduino library example:
+//   https://github.com/adafruit/Adafruit_Si5351_Library/blob/master/examples/si5351/si5351.ino
+// Which will configure the chip with:
+//  - PLL A at 900mhz
+//  - PLL B at 616.66667mhz
+//  - Clock 0 at 112.5mhz, using PLL A as a source divided by 8
+//  - Clock 1 at 13.5531mhz, using PLL B as a source divided by 45.5
+//  - Clock 2 at 10.76khz, using PLL B as a source divided by 900 and further divided with an R divider of 64.
+
+func main() {
+	time.Sleep(5 * time.Second)
+
+	println("Si5351 Clockgen Test")
+	println()
+
+	// Configure I2C bus
+	machine.I2C0.Configure(machine.I2CConfig{})
+
+	// Create driver instance
+	clockgen := si5351.New(machine.I2C0)
+
+	// Verify device wired properly
+	connected, err := clockgen.Connected()
+	if err != nil {
+		println("Unable to read device status")
+		time.Sleep(time.Second)
+	}
+	if !connected {
+		for {
+			println("Unable to detect si5351 device")
+			time.Sleep(time.Second)
+		}
+	}
+
+	// Initialise device
+	clockgen.Configure()
+
+	// Now configue the PLLs and clock outputs.
+	// The PLLs can be configured with a multiplier and division of the on-board
+	// 25mhz reference crystal.  For example configure PLL A to 900mhz by multiplying
+	// by 36.  This uses an integer multiplier which is more accurate over time
+	// but allows less of a range of frequencies compared to a fractional
+	// multiplier shown next.
+	clockgen.ConfigurePLL(si5351.PLL_A, 36, 0, 1) // Multiply 25mhz by 36
+	println("PLL A frequency: 900mhz")
+
+	// And next configure PLL B to 616.6667mhz by multiplying 25mhz by 24.667 using
+	// the fractional multiplier configuration.  Notice you specify the integer
+	// multiplier and then a numerator and denominator as separate values, i.e.
+	// numerator 2 and denominator 3 means 2/3 or 0.667.  This fractional
+	// configuration is susceptible to some jitter over time but can set a larger
+	// range of frequencies.
+	clockgen.ConfigurePLL(si5351.PLL_B, 24, 2, 3) // Multiply 25mhz by 24.667 (24 2/3)
+	println("PLL B frequency: 616.6667mhz")
+
+	// Now configure the clock outputs.  Each is driven by a PLL frequency as input
+	// and then further divides that down to a specific frequency.
+	// Configure clock 0 output to be driven by PLL A divided by 8, so an output
+	// of 112.5mhz (900mhz / 8).  Again this uses the most precise integer division
+	// but can't set as wide a range of values.
+	clockgen.ConfigureMultisynth(0, si5351.PLL_A, 8, 0, 1) // Divide by 8 (8 0/1)
+	println("Clock 0: 112.5mhz")
+
+	// Next configure clock 1 to be driven by PLL B divided by 45.5 to get
+	// 13.5531mhz (616.6667mhz / 45.5).  This uses fractional division and again
+	// notice the numerator and denominator are explicitly specified.  This is less
+	// precise but allows a large range of frequencies.
+	clockgen.ConfigureMultisynth(1, si5351.PLL_B, 45, 1, 2) // Divide by 45.5 (45 1/2)
+	println("Clock 1: 13.5531mhz")
+
+	// Finally configure clock 2 to be driven by PLL B divided once by 900 to get
+	// down to 685.15 khz and then further divided by a special R divider that
+	// divides 685.15 khz by 64 to get a final output of 10.706khz.
+	clockgen.ConfigureMultisynth(2, si5351.PLL_B, 900, 0, 1) // Divide by 900 (900 0/1)
+	// Set the R divider, this can be a value of:
+	//  - R_DIV_1: divider of 1
+	//  - R_DIV_2: divider of 2
+	//  - R_DIV_4: divider of 4
+	//  - R_DIV_8: divider of 8
+	//  - R_DIV_16: divider of 16
+	//  - R_DIV_32: divider of 32
+	//  - R_DIV_64: divider of 64
+	//  - R_DIV_128: divider of 128
+	clockgen.ConfigureRdiv(2, si5351.R_DIV_64)
+	println("Clock 2: 10.706khz")
+
+	// After configuring PLLs and clocks, enable the outputs.
+	clockgen.EnableOutputs()
+
+	for {
+		time.Sleep(5 * time.Second)
+		println()
+		println("Clock 0: 112.5mhz")
+		println("Clock 1: 13.5531mhz")
+		println("Clock 2: 10.706khz")
+	}
+}