rp2040: SPI implementation

[soypat]

Not tested yet. I've never contributed before and looking forward to learning what the workflow looks like. Solves #1987

[soypat]

Let me know of any comments so I can apply fixes and suggestions to i2c and PWM implementation branches!

[efectn]

Have you tested yet? If not, i can test when i'm free.

[soypat]

Have you tested yet? If not, i can test when i'm free.

@efectn I have not. Having trouble building TinyGo :(

[soypat]

I've managed to build tinygo and flash programs to the pico. Currently dont have SPI devices on hand so I'll probably be PRing the i2c branch as soon as I get it working and then fix this branch (already noticed a couple bugs in how I use ReplaceBits)

[soypat]

So I have not gotten the driver working. I'm going to take a break from this driver and try the PWM out. I've managed to get the Loopback function working but struggling reading data from my SPI device (see details below).

Example program with loopback test

package main

import (
	"device/rp"
	"machine"
	"time"
)

var (
	LED  = machine.GPIO25
	b    = machine.SPI{Bus: rp.SPI0}
	uart = machine.UART0
	MISO = machine.GPIO4
	CS   = machine.GPIO5
	SCK  = machine.GPIO6
	MOSI = machine.GPIO7
)

func main() {
	// configure UART to print stuff
	{
		err := uart.Configure(machine.UARTConfig{BaudRate: 9600})
		if err != nil {
			panic(err)
		}
	}
	println("start program")
	time.Sleep(time.Millisecond)

	err := b.Configure(machine.SPIConfig{Frequency: 8.1e6,
		SDO: MOSI,
		SDI: MISO,
		SCK: SCK})

	if err != nil {
		println(err.Error())
	} else {
		println("spi baud:", b.GetBaudRate())
	}
	// Loopback test.
	b.Bus.SSPCR1.SetBits(rp.SPI0_SSPCR1_LBM)
	for i := 0; i < 10; i++ {
		ret, err := b.Transfer(uint8(i))
		if err != nil {
			println(err.Error())
		}
		println(i, ret)
	}
	// Output:
	// 0 0
	// 1 1
	// 2 2
	// 3 3
	// 4 4
	// 5 5
	// 6 6
	// 7 7
	// 8 8
	// 9 9
	// End loopback test.
	b.Bus.SSPCR1.ClearBits(rp.SPI0_SSPCR1_LBM)

	LED.Configure(machine.PinConfig{Mode: machine.PinOutput})
	CS.Configure(machine.PinConfig{Mode: machine.PinInputPullup})
	CS.Configure(machine.PinConfig{Mode: machine.PinOutput})
	CS.High() // Motorola SPI has Active Low.
	// Do SPI stuff
	for { // blinky when done.
		time.Sleep(time.Second)
		LED.Set(!LED.Get())
	}
}

[deadprogram]

In order to test this on my rp2040 pico board, I had to add the following code:

diff --git a/src/machine/board_pico.go b/src/machine/board_pico.go
index 3a4d67b..e60fbec 100644
--- a/src/machine/board_pico.go
+++ b/src/machine/board_pico.go
@@ -2,6 +2,10 @@
 
 package machine
 
+import (
+       "device/rp"
+)
+
 // GPIO pins
 const (
        GP0  Pin = GPIO0
@@ -37,3 +41,18 @@ const (
        // Onboard crystal oscillator frequency, in MHz.
        xoscFreq = 12 // MHz
 )
+
+// SPI pins
+const (
+       SPI0_SCK_PIN Pin = GPIO18
+       SPI0_SDO_PIN Pin = GPIO19
+       SPI0_SDI_PIN Pin = GPIO16
+)
+
+// SPI on the RP2040
+var (
+       SPI0  = &_SPI0
+       _SPI0 = SPI{
+               Bus: rp.SPI0,
+       }
+)

SPI0 needs to be hooked up to a specific bus for it to be able to be used. The pin definitions are just added for clarity. See my comments above.

[deadprogram]

By the way, the SPI interface worked on my pico using an APA102 LED strip. Good work @soypat!

[deadprogram]

I think you still need to add the following to machine_rp2040.go:

// SPI on the RP2040
var (
	SPI0  = &_SPI0
	_SPI0 = SPI{
		Bus: rp.SPI0,
	}
	SPI1  = &_SPI1
	_SPI1 = SPI{
		Bus: rp.SPI1,
	}
)

Add that, and squash everything into a single commit, and I think we are about ready to merge this! 😸

[deadprogram]

Thanks very much for all the work on this PR! Now merging.