main: detect specific serial port IDs based on USB vid/pid

This makes it possible to flash a board even when there are multiple
different kinds of boards attached, e.g. an Arduino Uno and a Circuit
Playground Express. You can find the VID/PID pair in several ways:

 1. By running `lsusb` before and after attaching the board and looking
    at the new USB device.
 2. By grepping for `usb_PID` and `usb_VID` in the TinyGo source code.
 3. By checking the Arduino IDE boards.txt from the vendor.

Note that one board may have multiple VID/PID pairs:

  * The bootloader and main program may have a different PID, so far
    I've seen that the main program generally has the bootloader PID
    with 0x8000 added.
  * The software running on the board may have an erroneous PID, for
    example from a different board. I've seen this happen a few times.
  * A single board may have had some revisions which changed the PID.
    This is particularly true for the Arduino Uno.

As a fallback, if the given VID/PID pair isn't found, the whole set of
serial ports will be used.

There are many boards which I haven't included yet simply because I
couldn't test them.

compileopts/target.go

@@ -45,6 +45,7 @@ type TargetSpec struct {
 	FlashCommand     string   `json:"flash-command"`
 	GDB              []string `json:"gdb"`
 	PortReset        string   `json:"flash-1200-bps-reset"`
+	SerialPort       []string `json:"serial-port"` // serial port IDs in the form "acm:vid:pid" or "usb:vid:pid"
 	FlashMethod      string   `json:"flash-method"`
 	FlashVolume      string   `json:"msd-volume-name"`
 	FlashFilename    string   `json:"msd-firmware-name"`

main.go

@@ -15,6 +15,7 @@ import (
 	"path/filepath"
 	"regexp"
 	"runtime"
+	"strconv"
 	"strings"
 	"sync/atomic"
 	"time"
@@ -296,7 +297,7 @@ func Flash(pkgName, port string, options *compileopts.Options) error {
 	return builder.Build(pkgName, fileExt, config, func(result builder.BuildResult) error {
 		// do we need port reset to put MCU into bootloader mode?
 		if config.Target.PortReset == "true" && flashMethod != "openocd" {
-			port, err := getDefaultPort(strings.FieldsFunc(port, func(c rune) bool { return c == ',' }))
+			port, err := getDefaultPort(port, config.Target.SerialPort)
 			if err != nil {
 				return err
 			}
@@ -321,7 +322,7 @@ func Flash(pkgName, port string, options *compileopts.Options) error {
 
 			if strings.Contains(flashCmd, "{port}") {
 				var err error
-				port, err = getDefaultPort(strings.FieldsFunc(port, func(c rune) bool { return c == ',' }))
+				port, err = getDefaultPort(port, config.Target.SerialPort)
 				if err != nil {
 					return err
 				}
@@ -718,7 +719,8 @@ func windowsFindUSBDrive(volume string, options *compileopts.Options) (string, e
 }
 
 // getDefaultPort returns the default serial port depending on the operating system.
-func getDefaultPort(portCandidates []string) (port string, err error) {
+func getDefaultPort(portFlag string, usbInterfaces []string) (port string, err error) {
+	portCandidates := strings.FieldsFunc(portFlag, func(c rune) bool { return c == ',' })
 	if len(portCandidates) == 1 {
 		return portCandidates[0], nil
 	}
@@ -734,13 +736,70 @@ func getDefaultPort(portCandidates []string) (port string, err error) {
 			return "", err
 		}
 
+		var preferredPortIDs [][2]uint16
+		for _, s := range usbInterfaces {
+			parts := strings.Split(s, ":")
+			if len(parts) != 3 || (parts[0] != "acm" && parts[0] == "usb") {
+				// acm and usb are the two types of serial ports recognized
+				// under Linux (ttyACM*, ttyUSB*). Other operating systems don't
+				// generally make this distinction. If this is not one of the
+				// given USB devices, don't try to parse the USB IDs.
+				continue
+			}
+			vid, err := strconv.ParseUint(parts[1], 16, 16)
+			if err != nil {
+				return "", fmt.Errorf("could not parse USB vendor ID %q: %w", parts[1], err)
+			}
+			pid, err := strconv.ParseUint(parts[2], 16, 16)
+			if err != nil {
+				return "", fmt.Errorf("could not parse USB product ID %q: %w", parts[1], err)
+			}
+			preferredPortIDs = append(preferredPortIDs, [2]uint16{uint16(vid), uint16(pid)})
+		}
+
+		var primaryPorts []string   // ports picked from preferred USB VID/PID
+		var secondaryPorts []string // other ports (as a fallback)
 		for _, p := range portsList {
-			if p.IsUSB {
-				ports = append(ports, p.Name)
+			if !p.IsUSB {
+				continue
 			}
+			if p.VID != "" && p.PID != "" {
+				foundPort := false
+				vid, vidErr := strconv.ParseUint(p.VID, 16, 16)
+				pid, pidErr := strconv.ParseUint(p.PID, 16, 16)
+				if vidErr == nil && pidErr == nil {
+					for _, id := range preferredPortIDs {
+						if uint16(vid) == id[0] && uint16(pid) == id[1] {
+							primaryPorts = append(primaryPorts, p.Name)
+							foundPort = true
+							continue
+						}
+					}
+				}
+				if foundPort {
+					continue
+				}
+			}
+
+			secondaryPorts = append(secondaryPorts, p.Name)
+		}
+		if len(primaryPorts) == 1 {
+			// There is exactly one match in the set of preferred ports. Use
+			// this port, even if there may be others available. This allows
+			// flashing a specific board even if there are multiple available.
+			return primaryPorts[0], nil
+		} else if len(primaryPorts) > 1 {
+			// There are multiple preferred ports, probably because more than
+			// one device of the same type are connected (e.g. two Arduino
+			// Unos).
+			ports = primaryPorts
+		} else {
+			// No preferred ports found. Fall back to other serial ports
+			// available in the system.
+			ports = secondaryPorts
 		}
 
-		if ports == nil || len(ports) == 0 {
+		if len(ports) == 0 {
 			// fallback
 			switch runtime.GOOS {
 			case "darwin":

targets/arduino-nano33.json

@@ -2,5 +2,6 @@
     "inherits": ["atsamd21g18a"],
     "build-tags": ["arduino_nano33"],
     "flash-command": "bossac -i -e -w -v -R -U --port={port} --offset=0x2000 {bin}",
+    "serial-port": ["acm:2341:8057", "acm:2341:0057"],
     "flash-1200-bps-reset": "true"
 }

targets/arduino.json

@@ -6,5 +6,6 @@
 		"-Wl,--defsym=_stack_size=512"
 	],
 	"flash-command": "avrdude -c arduino -p atmega328p -P {port} -U flash:w:{hex}:i",
+	"serial-port": ["acm:2341:0043", "acm:2341:0001", "acm:2a03:0043", "acm:2341:0243"],
 	"emulator": ["simavr", "-m", "atmega328p", "-f", "16000000"]
 }

targets/circuitplay-bluefruit.json

@@ -3,6 +3,7 @@
     "build-tags": ["circuitplay_bluefruit","nrf52840_reset_uf2", "softdevice", "s140v6"],
     "flash-1200-bps-reset": "true",
     "flash-method": "msd",
+    "serial-port": ["acm:239a:8045", "acm:239a:45"],
     "msd-volume-name": "CPLAYBTBOOT",
     "msd-firmware-name": "firmware.uf2",
     "uf2-family-id": "0xADA52840",

targets/circuitplay-express.json

@@ -3,6 +3,7 @@
     "build-tags": ["circuitplay_express"],
     "flash-1200-bps-reset": "true",
     "flash-method": "msd",
+    "serial-port": ["acm:239a:8018", "acm:239a:18"],
     "msd-volume-name": "CPLAYBOOT",
     "msd-firmware-name": "firmware.uf2"
 }

targets/itsybitsy-m4.json

@@ -3,6 +3,7 @@
     "build-tags": ["itsybitsy_m4"],
     "flash-1200-bps-reset": "true",
     "flash-method": "msd",
+    "serial-port": ["acm:239a:802b", "acm:239a:002b"],
     "msd-volume-name": "ITSYM4BOOT",
     "msd-firmware-name": "firmware.uf2"
 }

targets/nano-33-ble.json

@@ -2,6 +2,7 @@
 	"inherits": ["nrf52840"],
 	"build-tags": ["nano_33_ble", "nrf52840_reset_bossa"],
 	"flash-command": "bossac_arduino2 -d -i -e -w -v -R --port={port} {bin}",
+	"serial-port": ["acm:2341:805a", "acm:2341:005a"],
 	"flash-1200-bps-reset": "true",
 	"linkerscript": "targets/nano-33-ble.ld"
 }

targets/pybadge.json

@@ -3,6 +3,7 @@
     "build-tags": ["pybadge"],
     "flash-1200-bps-reset": "true",
     "flash-method": "msd",
+    "serial-port": ["acm:239a:8033", "acm:239a:33"],
     "msd-volume-name": "PYBADGEBOOT",
     "msd-firmware-name": "arcade.uf2"
 }

targets/pyportal.json

@@ -3,6 +3,7 @@
     "build-tags": ["pyportal"],
     "flash-1200-bps-reset": "true",
     "flash-method": "msd",
+    "serial-port": ["acm:239a:8035", "acm:239a:35", "acm:239a:8036"],
     "msd-volume-name": "PORTALBOOT",
     "msd-firmware-name": "firmware.uf2"
 }