all: add a flag to the command line to select the serial implementation

This can be very useful for some purposes:

  * It makes it possible to disable the UART in cases where it is not
    needed or needs to be disabled to conserve power.
  * It makes it possible to disable the serial output to reduce code
    size, which may be important for some chips. Sometimes, a few kB can
    be saved this way.
  * It makes it possible to override the default, for example you might
    want to use an actual UART to debug the USB-CDC implementation.

It also lowers the dependency on having machine.Serial defined, which is
often not defined when targeting a chip. Eventually, we might want to
make it possible to write `-target=nrf52` or `-target=atmega328p` for
example to target the chip itself with no board specific assumptions.

The defaults don't change. I checked this by running `make smoketest`
before and after and comparing the results.

targets/arduino-mkr1000.json

@@ -1,6 +1,7 @@
 {
     "inherits": ["atsamd21g18a"],
     "build-tags": ["arduino_mkr1000"],
+	"serial": "usb",
     "flash-command": "bossac -i -e -w -v -R -U --port={port} --offset=0x2000 {bin}",
     "flash-1200-bps-reset": "true"
 }

targets/arduino-zero.json

@@ -1,6 +1,7 @@
 {
     "inherits": ["atsamd21g18a"],
     "build-tags": ["arduino_zero"],
+	"serial": "usb",
     "flash-command": "bossac -i -e -w -v -R -U --port={port} --offset=0x2000 {bin}",
     "flash-1200-bps-reset": "true"
 }

targets/atmega1280.json

@@ -2,6 +2,7 @@
     "inherits": ["avr"],
     "cpu": "atmega1280",
     "build-tags": ["atmega1280", "atmega"],
+    "serial": "uart",
     "cflags": [
         "-mmcu=atmega1280"
     ],

targets/atmega1284p.json

@@ -2,6 +2,7 @@
     "inherits": ["avr"],
     "cpu": "atmega1284p",
     "build-tags": ["atmega1284p", "atmega"],
+    "serial": "uart",
     "cflags": [
         "-mmcu=atmega1284p"
     ],

targets/atmega2560.json

@@ -2,6 +2,7 @@
     "inherits": ["avr"],
     "cpu": "atmega2560",
     "build-tags": ["atmega2560", "atmega"],
+    "serial": "uart",
     "cflags": [
         "-mmcu=atmega2560"
     ],

targets/atmega328p.json

@@ -2,6 +2,7 @@
 	"inherits": ["avr"],
 	"cpu": "atmega328p",
 	"build-tags": ["atmega328p", "atmega", "avr5"],
+	"serial": "uart",
 	"cflags": [
 		"-mmcu=atmega328p"
 	],

targets/atsamd21e18a.json

@@ -1,6 +1,7 @@
 {
 	"inherits": ["cortex-m0plus"],
 	"build-tags": ["atsamd21e18a", "atsamd21e18", "atsamd21", "sam"],
+	"serial": "usb",
 	"linkerscript": "targets/atsamd21.ld",
 	"extra-files": [
 		"src/device/sam/atsamd21e18a.s"

targets/atsamd21g18a.json

@@ -1,6 +1,7 @@
 {
 	"inherits": ["cortex-m0plus"],
 	"build-tags": ["atsamd21g18a", "atsamd21g18", "atsamd21", "sam"],
+	"serial": "usb",
 	"linkerscript": "targets/atsamd21.ld",
 	"extra-files": [
 		"src/device/sam/atsamd21g18a.s"

targets/atsame54-xpro.json

@@ -1,6 +1,7 @@
 {
     "inherits": ["atsame54p20a"],
     "build-tags": ["atsame54_xpro"],
+    "serial": "usb",
     "flash-method": "openocd",
     "openocd-interface": "cmsis-dap",
     "default-stack-size": 4096

targets/bluepill.json

@@ -1,6 +1,7 @@
 {
 	"inherits": ["cortex-m3"],
 	"build-tags": ["bluepill", "stm32f103", "stm32f1", "stm32"],
+	"serial": "uart",
 	"linkerscript": "targets/stm32.ld",
 	"extra-files": [
 		"src/device/stm32/stm32f103.s"

targets/circuitplay-bluefruit.json

@@ -1,6 +1,7 @@
 {
     "inherits": ["nrf52840"],
     "build-tags": ["circuitplay_bluefruit","nrf52840_reset_uf2", "softdevice", "s140v6"],
+    "serial": "usb",
     "flash-1200-bps-reset": "true",
     "flash-method": "msd",
     "serial-port": ["acm:239a:8045", "acm:239a:45"],

targets/clue-alpha.json

@@ -1,6 +1,7 @@
 {
     "inherits": ["nrf52840"],
     "build-tags": ["clue_alpha","nrf52840_reset_uf2", "softdevice", "s140v6"],
+    "serial": "usb",
     "flash-1200-bps-reset": "true",
     "flash-method": "msd",
     "msd-volume-name": "CLUEBOOT",

targets/esp32.json

@@ -3,6 +3,7 @@
 	"cpu": "esp32",
 	"build-tags": ["esp32", "esp"],
 	"scheduler": "tasks",
+	"serial": "uart",
 	"linker": "xtensa-esp32-elf-ld",
 	"default-stack-size": 2048,
 	"cflags": [

targets/feather-m4-can.json

@@ -1,6 +1,7 @@
 {
     "inherits": ["atsame51j19a"],
     "build-tags": ["feather_m4_can"],
+    "serial": "usb",
     "flash-1200-bps-reset": "true",
     "flash-method": "msd",
     "msd-volume-name": "FTHRCANBOOT",

targets/feather-m4.json

@@ -1,6 +1,7 @@
 {
     "inherits": ["atsamd51j19a"],
     "build-tags": ["feather_m4"],
+    "serial": "usb",
     "flash-1200-bps-reset": "true",
     "flash-method": "msd",
     "msd-volume-name": "FEATHERBOOT",

targets/feather-nrf52840.json

@@ -1,6 +1,7 @@
 {
     "inherits": ["nrf52840"],
     "build-tags": ["feather_nrf52840","nrf52840_reset_uf2", "softdevice", "s140v6"],
+    "serial": "usb",
     "flash-1200-bps-reset": "true",
     "flash-method": "msd",
     "msd-volume-name": "FTHR840BOOT",

targets/feather-stm32f405.json

@@ -1,6 +1,7 @@
 {
   "inherits": ["cortex-m4"],
   "build-tags": ["feather_stm32f405", "stm32f405", "stm32f4", "stm32"],
+  "serial": "uart",
   "automatic-stack-size": false,
   "linkerscript": "targets/stm32f405.ld",
   "extra-files": [

targets/grandcentral-m4.json

@@ -1,6 +1,7 @@
 {
     "inherits": ["atsamd51p20a"],
     "build-tags": ["grandcentral_m4"],
+    "serial": "usb",
     "flash-1200-bps-reset": "true",
     "flash-method": "msd",
     "msd-volume-name": "GCM4BOOT",

targets/hifive1-qemu.json

@@ -1,6 +1,7 @@
 {
 	"inherits": ["fe310"],
 	"build-tags": ["hifive1b", "qemu"],
+	"serial": "uart",
 	"linkerscript": "targets/hifive1-qemu.ld",
 	"emulator": ["qemu-system-riscv32", "-machine", "sifive_e", "-nographic", "-kernel"]
 }

targets/hifive1b.json

@@ -1,6 +1,7 @@
 {
 	"inherits": ["fe310"],
 	"build-tags": ["hifive1b"],
+	"serial": "uart",
 	"linkerscript": "targets/hifive1b.ld",
 	"flash-method": "msd",
 	"msd-volume-name": "HiFive",

targets/itsybitsy-m4.json

@@ -1,6 +1,7 @@
 {
     "inherits": ["atsamd51g19a"],
     "build-tags": ["itsybitsy_m4"],
+    "serial": "usb",
     "flash-1200-bps-reset": "true",
     "flash-method": "msd",
     "serial-port": ["acm:239a:802b", "acm:239a:002b"],

targets/itsybitsy-nrf52840.json

@@ -1,6 +1,7 @@
 {
     "inherits": ["nrf52840"],
     "build-tags": ["itsybitsy_nrf52840","nrf52840_reset_uf2", "softdevice", "s140v6"],
+    "serial": "usb",
     "flash-1200-bps-reset": "true",
     "flash-method": "msd",
     "msd-volume-name": "ITSY840BOOT",

targets/lgt92.json

@@ -5,6 +5,7 @@
 	"build-tags": [
 		"lgt92"
 	],
+	"serial": "uart",
 	"linkerscript": "targets/stm32l072czt6.ld",
 	"flash-method": "openocd",
 	"openocd-interface": "stlink-v2",

targets/maixbit.json

@@ -1,6 +1,7 @@
 {
 	"inherits": ["k210"],
 	"build-tags": ["maixbit"],
+	"serial": "uart",
 	"linkerscript": "targets/maixbit.ld",
 	"flash-command": "kflash -p {port} --noansi --verbose {bin}"
 }

targets/metro-m4-airlift.json

@@ -1,6 +1,7 @@
 {
     "inherits": ["atsamd51j19a"],
     "build-tags": ["metro_m4_airlift"],
+    "serial": "usb",
     "flash-1200-bps-reset": "true",
     "flash-method": "msd",
     "msd-volume-name": "METROM4BOOT",

targets/microbit-v2.json

@@ -1,6 +1,7 @@
 {
 	"inherits": ["nrf52833"],
 	"build-tags": ["microbit_v2"],
+	"serial": "uart",
 	"flash-method": "msd",
 	"openocd-interface": "cmsis-dap",
 	"msd-volume-name": "MICROBIT",

targets/microbit.json

@@ -1,6 +1,7 @@
 {
 	"inherits": ["nrf51"],
 	"build-tags": ["microbit"],
+	"serial": "uart",
 	"flash-method": "msd",
 	"openocd-interface": "cmsis-dap",
 	"msd-volume-name": "MICROBIT",

targets/nicenano.json

@@ -1,6 +1,7 @@
 {
     "inherits": ["nrf52840"],
     "build-tags": ["nicenano","nrf52840_reset_uf2", "softdevice", "s140v6"],
+    "serial": "usb",
     "flash-1200-bps-reset": "true",
     "flash-method": "msd",
     "msd-volume-name": "NICENANO",

targets/nodemcu.json

@@ -1,4 +1,5 @@
 {
 	"inherits": ["esp8266"],
-	"build-tags": ["nodemcu"]
+	"build-tags": ["nodemcu"],
+	"serial": "uart"
 }

targets/nrf52840-mdk-usb-dongle.json

@@ -1,6 +1,7 @@
 {
     "inherits": ["nrf52840"],
     "build-tags": ["nrf52840_mdk_usb_dongle", "nrf52840_reset_uf2", "softdevice", "s140v6"],
+    "serial": "usb",
     "flash-1200-bps-reset": "true",
     "flash-method": "msd",
     "msd-volume-name": "MDK-DONGLE",

targets/nrf52840-mdk.json

@@ -1,6 +1,7 @@
 {
 	"inherits": ["nrf52840"],
 	"build-tags": ["nrf52840_mdk"],
+	"serial": "usb",
 	"flash-method": "openocd",
 	"openocd-interface": "cmsis-dap"
 }

targets/nucleo-f103rb.json

@@ -1,6 +1,7 @@
 {
   "inherits": ["cortex-m3"],
   "build-tags": ["nucleof103rb", "stm32f103", "stm32f1","stm32"],
+  "serial": "uart",
   "linkerscript": "targets/stm32f103rb.ld",
   "extra-files": [
     "src/device/stm32/stm32f103.s"

targets/nucleo-f722ze.json

@@ -1,6 +1,7 @@
 {
   "inherits": ["cortex-m7"],
   "build-tags": ["nucleof722ze", "stm32f7x2", "stm32f7", "stm32"],
+  "serial": "uart",
   "linkerscript": "targets/stm32f7x2zetx.ld",
   "extra-files": [
     "src/device/stm32/stm32f7x2.s"

targets/nucleo-l031k6.json

@@ -1,6 +1,7 @@
 {
     "inherits": ["cortex-m0"],
     "build-tags": ["nucleol031k6", "stm32l031", "stm32l0x1", "stm32l0", "stm32"],
+    "serial": "uart",
     "linkerscript": "targets/stm32l031k6.ld",
     "extra-files": [
         "src/device/stm32/stm32l0x1.s"

targets/nucleo-l432kc.json

@@ -1,6 +1,7 @@
 {
     "inherits": ["cortex-m4"],
     "build-tags": ["nucleol432kc", "stm32l432", "stm32l4x2", "stm32l4", "stm32"],
+    "serial": "uart",
     "linkerscript": "targets/stm32l4x2.ld",
     "extra-files": [
       "src/device/stm32/stm32l4x2.s"

targets/nucleo-l552ze.json

@@ -1,6 +1,7 @@
 {
     "inherits": ["cortex-m33"],
     "build-tags": ["nucleol552ze", "stm32l552", "stm32l5x2", "stm32l5", "stm32"],
+    "serial": "uart",
     "linkerscript": "targets/stm32l5x2xe.ld",
     "extra-files": [
       "src/device/stm32/stm32l552.s"

targets/particle-3rd-gen.json

@@ -1,6 +1,7 @@
 {
 	"inherits": ["nrf52840"],
 	"build-tags": ["particle_3rd_gen"],
+	"serial": "uart",
 	"flash-method": "openocd",
 	"openocd-interface": "cmsis-dap"
 }

targets/pca10031.json

@@ -1,6 +1,7 @@
 {
 	"inherits": ["nrf51"],
 	"build-tags": ["pca10031"],
+	"serial": "uart",
 	"flash-command": "nrfjprog -f nrf51 --sectorerase --program {hex} --reset",
 	"openocd-interface": "cmsis-dap"
 }

targets/pca10040.json

@@ -1,6 +1,7 @@
 {
 	"inherits": ["nrf52"],
 	"build-tags": ["pca10040"],
+	"serial": "uart",
 	"flash-method": "openocd",
 	"flash-command": "nrfjprog -f nrf52 --sectorerase --program {hex} --reset",
 	"openocd-interface": "jlink",

targets/pca10056.json

@@ -1,6 +1,7 @@
 {
 	"inherits": ["nrf52840"],
 	"build-tags": ["pca10056"],
+	"serial": "uart",
 	"flash-method": "command",
 	"flash-command": "nrfjprog -f nrf52 --sectorerase --program {hex} --reset",
 	"msd-volume-name": "JLINK",

targets/pca10059.json

@@ -1,6 +1,7 @@
 {
 	"inherits": ["nrf52840"],
 	"build-tags": ["pca10059"],
+	"serial": "usb",
 	"linkerscript": "targets/pca10059.ld",
 	"binary-format": "nrf-dfu",
 	"flash-command": "nrfutil dfu usb-serial -pkg {zip} -p {port} -b 115200"

targets/pico.json

@@ -3,6 +3,7 @@
         "rp2040"
     ],
     "build-tags": ["pico"],
+    "serial": "uart",
     "linkerscript": "targets/pico.ld",
     "extra-files": [
         "targets/pico-boot-stage2.S"

targets/pinetime-devkit0.json

@@ -1,6 +1,7 @@
 {
 	"inherits": ["nrf52"],
 	"build-tags": ["pinetime_devkit0"],
+	"serial": "uart",
 	"flash-method": "openocd",
 	"flash-command": "nrfjprog -f nrf52 --sectorerase --program {hex} --reset",
 	"openocd-interface": "jlink",

targets/pybadge.json

@@ -1,6 +1,7 @@
 {
     "inherits": ["atsamd51j19a"],
     "build-tags": ["pybadge"],
+    "serial": "usb",
     "flash-1200-bps-reset": "true",
     "flash-method": "msd",
     "serial-port": ["acm:239a:8033", "acm:239a:33"],

targets/pygamer.json

@@ -1,6 +1,7 @@
 {
     "inherits": ["atsamd51j19a"],
     "build-tags": ["pygamer"],
+    "serial": "usb",
     "flash-1200-bps-reset": "true",
     "flash-method": "msd",
     "msd-volume-name": "PYGAMERBOOT",

targets/pyportal.json

@@ -1,6 +1,7 @@
 {
     "inherits": ["atsamd51j20a"],
     "build-tags": ["pyportal"],
+    "serial": "usb",
     "flash-1200-bps-reset": "true",
     "flash-method": "msd",
     "serial-port": ["acm:239a:8035", "acm:239a:35", "acm:239a:8036"],

targets/reelboard.json

@@ -1,6 +1,7 @@
 {
 	"inherits": ["nrf52840"],
 	"build-tags": ["reelboard"],
+	"serial": "uart",
 	"flash-method": "msd",
 	"msd-volume-name": "reel-board",
 	"msd-firmware-name": "firmware.hex",

targets/stm32f4disco.json

@@ -1,6 +1,7 @@
 {
   "inherits": ["cortex-m4"],
   "build-tags": ["stm32f4disco", "stm32f407", "stm32f4", "stm32"],
+  "serial": "uart",
   "linkerscript": "targets/stm32f407.ld",
   "extra-files": [
     "src/device/stm32/stm32f407.s"

targets/teensy36.json

@@ -1,6 +1,7 @@
 {
 	"inherits": ["cortex-m4"],
 	"build-tags": ["teensy36", "teensy", "mk66f18", "nxp"],
+	"serial": "uart",
 	"linkerscript": "targets/nxpmk66f18.ld",
 	"extra-files": [
 		"src/device/nxp/mk66f18.s",

targets/teensy40.json

@@ -1,6 +1,7 @@
 {
   "inherits": ["cortex-m7"],
   "build-tags": ["teensy40", "teensy", "mimxrt1062", "nxp"],
+  "serial": "uart",
   "automatic-stack-size": false,
   "default-stack-size": 4096,
   "linkerscript": "targets/mimxrt1062-teensy40.ld",

targets/wioterminal.json

@@ -1,6 +1,7 @@
 {
     "inherits": ["atsamd51p19a"],
     "build-tags": ["wioterminal"],
+    "serial": "usb",
     "flash-1200-bps-reset": "true",
     "flash-method": "msd",
     "msd-volume-name": "Arduino",

targets/x9pro.json

@@ -1,6 +1,7 @@
 {
 	"inherits": ["nrf52"],
 	"build-tags": ["x9pro"],
+	"serial": "uart",
 	"flash-method": "openocd",
 	"flash-command": "nrfjprog -f nrf52 --sectorerase --program {hex} --reset",
 	"openocd-interface": "jlink",