supports binary-format, only esp* supported for now

internal/build/build.go

@@ -42,6 +42,7 @@ import (
 	"github.com/goplus/llgo/internal/clang"
 	"github.com/goplus/llgo/internal/crosscompile"
 	"github.com/goplus/llgo/internal/env"
+	"github.com/goplus/llgo/internal/firmware"
 	"github.com/goplus/llgo/internal/mockable"
 	"github.com/goplus/llgo/internal/packages"
 	"github.com/goplus/llgo/internal/typepatch"
@@ -629,23 +630,76 @@ func compileExtraFiles(ctx *context, verbose bool) ([]string, error) {
 	return objFiles, nil
 }
 
-func linkMainPkg(ctx *context, pkg *packages.Package, pkgs []*aPackage, global llssa.Package, conf *Config, mode Mode, verbose bool) {
+// generateOutputFilenames generates the final output filename (app) and intermediate filename (orgApp)
-	pkgPath := pkg.PkgPath
+// based on configuration and build context.
-	name := path.Base(pkgPath)
+func generateOutputFilenames(outFile, binPath, appExt, binExt, pkgName string, mode Mode, isMultiplePkgs bool) (app, orgApp string, err error) {
-	app := conf.OutFile
+	if outFile == "" {
-	if app == "" {
+		if mode == ModeBuild && isMultiplePkgs {
-		if mode == ModeBuild && len(ctx.initial) > 1 {
 			// For multiple packages in ModeBuild mode, use temporary file
-			tmpFile, err := os.CreateTemp("", name+"*"+conf.AppExt)
+			name := pkgName
-			check(err)
+			if binExt != "" {
+				name += "*" + binExt
+			} else {
+				name += "*" + appExt
+			}
+			tmpFile, err := os.CreateTemp("", name)
+			if err != nil {
+				return "", "", err
+			}
 			app = tmpFile.Name()
 			tmpFile.Close()
 		} else {
-			app = filepath.Join(conf.BinPath, name+conf.AppExt)
+			app = filepath.Join(binPath, pkgName+appExt)
+		}
+		orgApp = app
+	} else {
+		// outFile is not empty, use it as base part
+		base := outFile
+		if binExt != "" {
+			// If binExt has value, use temporary file as orgApp for firmware conversion
+			tmpFile, err := os.CreateTemp("", "llgo-*"+appExt)
+			if err != nil {
+				return "", "", err
+			}
+			orgApp = tmpFile.Name()
+			tmpFile.Close()
+			// Check if base already ends with binExt, if so, don't add it again
+			if strings.HasSuffix(base, binExt) {
+				app = base
+			} else {
+				app = base + binExt
+			}
+		} else {
+			// No binExt, use base + AppExt directly
+			if filepath.Ext(base) == "" {
+				app = base + appExt
+			} else {
+				app = base
+			}
+			orgApp = app
 		}
-	} else if filepath.Ext(app) == "" {
-		app += conf.AppExt
 	}
+	return app, orgApp, nil
+}
+
+func linkMainPkg(ctx *context, pkg *packages.Package, pkgs []*aPackage, global llssa.Package, conf *Config, mode Mode, verbose bool) {
+	pkgPath := pkg.PkgPath
+	name := path.Base(pkgPath)
+	binFmt := ctx.crossCompile.BinaryFormat
+	binExt := firmware.BinaryExt(binFmt)
+
+	// app: converted firmware output file or executable file
+	// orgApp: before converted output file
+	app, orgApp, err := generateOutputFilenames(
+		conf.OutFile,
+		conf.BinPath,
+		conf.AppExt,
+		binExt,
+		name,
+		mode,
+		len(ctx.initial) > 1,
+	)
+	check(err)
 
 	needRuntime := false
 	needPyInit := false
@@ -701,9 +755,15 @@ func linkMainPkg(ctx *context, pkg *packages.Package, pkgs []*aPackage, global l
 		linkArgs = append(linkArgs, exargs...)
 	}
 
-	err = linkObjFiles(ctx, app, objFiles, linkArgs, verbose)
+	err = linkObjFiles(ctx, orgApp, objFiles, linkArgs, verbose)
 	check(err)
 
+	if orgApp != app {
+		fmt.Printf("cross compile: %#v\n", ctx.crossCompile)
+		err = firmware.MakeFirmwareImage(orgApp, app, ctx.crossCompile.BinaryFormat)
+		check(err)
+	}
+
 	switch mode {
 	case ModeTest:
 		cmd := exec.Command(app, conf.RunArgs...)

internal/build/build_test.go

@@ -8,6 +8,7 @@ import (
 	"fmt"
 	"io"
 	"os"
+	"strings"
 	"testing"
 
 	"github.com/goplus/llgo/internal/mockable"
@@ -93,3 +94,173 @@ func TestExtest(t *testing.T) {
 func TestCmpTest(t *testing.T) {
 	mockRun([]string{"../../cl/_testgo/runtest"}, &Config{Mode: ModeCmpTest})
 }
+
+func TestGenerateOutputFilenames(t *testing.T) {
+	tests := []struct {
+		name           string
+		outFile        string
+		binPath        string
+		appExt         string
+		binExt         string
+		pkgName        string
+		mode           Mode
+		isMultiplePkgs bool
+		wantAppSuffix  string
+		wantOrgAppDiff bool // true if orgApp should be different from app
+		wantErr        bool
+	}{
+		{
+			name:           "empty outFile, single package",
+			outFile:        "",
+			binPath:        "/usr/local/bin",
+			appExt:         "",
+			binExt:         "",
+			pkgName:        "hello",
+			mode:           ModeBuild,
+			isMultiplePkgs: false,
+			wantAppSuffix:  "/usr/local/bin/hello",
+			wantOrgAppDiff: false,
+		},
+		{
+			name:           "empty outFile with appExt",
+			outFile:        "",
+			binPath:        "/usr/local/bin",
+			appExt:         ".exe",
+			binExt:         "",
+			pkgName:        "hello",
+			mode:           ModeBuild,
+			isMultiplePkgs: false,
+			wantAppSuffix:  "/usr/local/bin/hello.exe",
+			wantOrgAppDiff: false,
+		},
+		{
+			name:           "outFile without binExt",
+			outFile:        "myapp",
+			binPath:        "/usr/local/bin",
+			appExt:         ".exe",
+			binExt:         "",
+			pkgName:        "hello",
+			mode:           ModeBuild,
+			isMultiplePkgs: false,
+			wantAppSuffix:  "myapp.exe",
+			wantOrgAppDiff: false,
+		},
+		{
+			name:           "outFile with existing extension, no binExt",
+			outFile:        "myapp.exe",
+			binPath:        "/usr/local/bin",
+			appExt:         ".exe",
+			binExt:         "",
+			pkgName:        "hello",
+			mode:           ModeBuild,
+			isMultiplePkgs: false,
+			wantAppSuffix:  "myapp.exe",
+			wantOrgAppDiff: false,
+		},
+		{
+			name:           "outFile with binExt, different from existing extension",
+			outFile:        "myapp",
+			binPath:        "/usr/local/bin",
+			appExt:         ".exe",
+			binExt:         ".bin",
+			pkgName:        "hello",
+			mode:           ModeBuild,
+			isMultiplePkgs: false,
+			wantAppSuffix:  "myapp.bin",
+			wantOrgAppDiff: true,
+		},
+		{
+			name:           "outFile already ends with binExt",
+			outFile:        "t.bin",
+			binPath:        "/usr/local/bin",
+			appExt:         ".exe",
+			binExt:         ".bin",
+			pkgName:        "hello",
+			mode:           ModeBuild,
+			isMultiplePkgs: false,
+			wantAppSuffix:  "t.bin",
+			wantOrgAppDiff: true,
+		},
+		{
+			name:           "outFile with full path already ends with binExt",
+			outFile:        "/path/to/t.bin",
+			binPath:        "/usr/local/bin",
+			appExt:         ".exe",
+			binExt:         ".bin",
+			pkgName:        "hello",
+			mode:           ModeBuild,
+			isMultiplePkgs: false,
+			wantAppSuffix:  "/path/to/t.bin",
+			wantOrgAppDiff: true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			app, orgApp, err := generateOutputFilenames(
+				tt.outFile,
+				tt.binPath,
+				tt.appExt,
+				tt.binExt,
+				tt.pkgName,
+				tt.mode,
+				tt.isMultiplePkgs,
+			)
+
+			if (err != nil) != tt.wantErr {
+				t.Errorf("generateOutputFilenames() error = %v, wantErr %v", err, tt.wantErr)
+				return
+			}
+
+			if tt.wantAppSuffix != "" {
+				if app != tt.wantAppSuffix {
+					t.Errorf("generateOutputFilenames() app = %v, want %v", app, tt.wantAppSuffix)
+				}
+			}
+
+			if tt.wantOrgAppDiff {
+				if app == orgApp {
+					t.Errorf("generateOutputFilenames() orgApp should be different from app, but both are %v", app)
+				}
+				// Clean up temp file
+				if orgApp != "" && strings.Contains(orgApp, "llgo-") {
+					os.Remove(orgApp)
+				}
+			} else {
+				if app != orgApp {
+					t.Errorf("generateOutputFilenames() orgApp = %v, want %v (same as app)", orgApp, app)
+				}
+			}
+		})
+	}
+}
+
+func TestGenerateOutputFilenames_EdgeCases(t *testing.T) {
+	// Test case where outFile has same extension as binExt
+	app, orgApp, err := generateOutputFilenames(
+		"firmware.bin",
+		"/usr/local/bin",
+		".exe",
+		".bin",
+		"esp32app",
+		ModeBuild,
+		false,
+	)
+
+	if err != nil {
+		t.Fatalf("Unexpected error: %v", err)
+	}
+
+	if app != "firmware.bin" {
+		t.Errorf("Expected app to be 'firmware.bin', got '%s'", app)
+	}
+
+	if app == orgApp {
+		t.Errorf("Expected orgApp to be different from app when binExt is present, but both are '%s'", app)
+	}
+
+	// Clean up temp file
+	if orgApp != "" && strings.Contains(orgApp, "llgo-") {
+		os.Remove(orgApp)
+	}
+}

internal/crosscompile/crosscompile.go

@@ -29,6 +29,8 @@ type Export struct {
 	ExtraFiles   []string // Extra files to compile and link (e.g., .s, .c files)
 	ClangRoot    string   // Root directory of custom clang installation
 	ClangBinPath string   // Path to clang binary directory
+
+	BinaryFormat string // Binary format (e.g., "elf", "esp", "uf2")
 }
 
 const wasiSdkUrl = "https://github.com/WebAssembly/wasi-sdk/releases/download/wasi-sdk-25/wasi-sdk-25.0-x86_64-macos.tar.gz"
@@ -447,6 +449,7 @@ func useTarget(targetName string) (export Export, err error) {
 	export.GOOS = config.GOOS
 	export.GOARCH = config.GOARCH
 	export.ExtraFiles = config.ExtraFiles
+	export.BinaryFormat = config.BinaryFormat
 
 	// Build environment map for template variable expansion
 	envs := buildEnvMap(env.LLGoROOT())

internal/firmware/esp.go

@@ -0,0 +1,188 @@
+package firmware
+
+import (
+	"bytes"
+	"crypto/sha256"
+	"debug/elf"
+	"encoding/binary"
+	"fmt"
+	"os"
+	"sort"
+	"strings"
+)
+
+// From tinygo/builder/esp.go
+
+type espImageSegment struct {
+	addr uint32
+	data []byte
+}
+
+// makeESPFirmareImage converts an input ELF file to an image file for an ESP32 or
+// ESP8266 chip. This is a special purpose image format just for the ESP chip
+// family, and is parsed by the on-chip mask ROM bootloader.
+//
+// The following documentation has been used:
+// https://github.com/espressif/esptool/wiki/Firmware-Image-Format
+// https://github.com/espressif/esp-idf/blob/8fbb63c2a701c22ccf4ce249f43aded73e134a34/components/bootloader_support/include/esp_image_format.h#L58
+// https://github.com/espressif/esptool/blob/master/esptool.py
+func makeESPFirmareImage(infile, outfile, format string) error {
+	inf, err := elf.Open(infile)
+	if err != nil {
+		return err
+	}
+	defer inf.Close()
+
+	// Load all segments to be written to the image. These are actually ELF
+	// sections, not true ELF segments (similar to how esptool does it).
+	var segments []*espImageSegment
+	for _, section := range inf.Sections {
+		if section.Type != elf.SHT_PROGBITS || section.Size == 0 || section.Flags&elf.SHF_ALLOC == 0 {
+			continue
+		}
+		data, err := section.Data()
+		if err != nil {
+			return fmt.Errorf("failed to read section data: %w", err)
+		}
+		for len(data)%4 != 0 {
+			// Align segment to 4 bytes.
+			data = append(data, 0)
+		}
+		if uint64(uint32(section.Addr)) != section.Addr {
+			return fmt.Errorf("section address too big: 0x%x", section.Addr)
+		}
+		segments = append(segments, &espImageSegment{
+			addr: uint32(section.Addr),
+			data: data,
+		})
+	}
+
+	// Sort the segments by address. This is what esptool does too.
+	sort.SliceStable(segments, func(i, j int) bool { return segments[i].addr < segments[j].addr })
+
+	// Calculate checksum over the segment data. This is used in the image
+	// footer.
+	checksum := uint8(0xef)
+	for _, segment := range segments {
+		for _, b := range segment.data {
+			checksum ^= b
+		}
+	}
+
+	// Write first to an in-memory buffer, primarily so that we can easily
+	// calculate a hash over the entire image.
+	// An added benefit is that we don't need to check for errors all the time.
+	outf := &bytes.Buffer{}
+
+	// Separate esp32 and esp32-img. The -img suffix indicates we should make an
+	// image, not just a binary to be flashed at 0x1000 for example.
+	chip := format
+	makeImage := false
+	if strings.HasSuffix(format, "-img") {
+		makeImage = true
+		chip = format[:len(format)-len("-img")]
+	}
+
+	if makeImage {
+		// The bootloader starts at 0x1000, or 4096.
+		// TinyGo doesn't use a separate bootloader and runs the entire
+		// application in the bootloader location.
+		outf.Write(make([]byte, 4096))
+	}
+
+	// Chip IDs. Source:
+	// https://github.com/espressif/esp-idf/blob/v4.3/components/bootloader_support/include/esp_app_format.h#L22
+	chip_id := map[string]uint16{
+		"esp32":   0x0000,
+		"esp32c3": 0x0005,
+	}[chip]
+
+	// Image header.
+	switch chip {
+	case "esp32", "esp32c3":
+		// Header format:
+		// https://github.com/espressif/esp-idf/blob/v4.3/components/bootloader_support/include/esp_app_format.h#L71
+		// Note: not adding a SHA256 hash as the binary is modified by
+		// esptool.py while flashing and therefore the hash won't be valid
+		// anymore.
+		binary.Write(outf, binary.LittleEndian, struct {
+			magic          uint8
+			segment_count  uint8
+			spi_mode       uint8
+			spi_speed_size uint8
+			entry_addr     uint32
+			wp_pin         uint8
+			spi_pin_drv    [3]uint8
+			chip_id        uint16
+			min_chip_rev   uint8
+			reserved       [8]uint8
+			hash_appended  bool
+		}{
+			magic:          0xE9,
+			segment_count:  byte(len(segments)),
+			spi_mode:       2,    // ESP_IMAGE_SPI_MODE_DIO
+			spi_speed_size: 0x1f, // ESP_IMAGE_SPI_SPEED_80M, ESP_IMAGE_FLASH_SIZE_2MB
+			entry_addr:     uint32(inf.Entry),
+			wp_pin:         0xEE, // disable WP pin
+			chip_id:        chip_id,
+			hash_appended:  true, // add a SHA256 hash
+		})
+	case "esp8266":
+		// Header format:
+		// https://github.com/espressif/esptool/wiki/Firmware-Image-Format
+		// Basically a truncated version of the ESP32 header.
+		binary.Write(outf, binary.LittleEndian, struct {
+			magic          uint8
+			segment_count  uint8
+			spi_mode       uint8
+			spi_speed_size uint8
+			entry_addr     uint32
+		}{
+			magic:          0xE9,
+			segment_count:  byte(len(segments)),
+			spi_mode:       0,    // irrelevant, replaced by esptool when flashing
+			spi_speed_size: 0x20, // spi_speed, spi_size: replaced by esptool when flashing
+			entry_addr:     uint32(inf.Entry),
+		})
+	default:
+		return fmt.Errorf("builder: unknown binary format %#v, expected esp32 or esp8266", format)
+	}
+
+	// Write all segments to the image.
+	// https://github.com/espressif/esptool/wiki/Firmware-Image-Format#segment
+	for _, segment := range segments {
+		binary.Write(outf, binary.LittleEndian, struct {
+			addr   uint32
+			length uint32
+		}{
+			addr:   segment.addr,
+			length: uint32(len(segment.data)),
+		})
+		outf.Write(segment.data)
+	}
+
+	// Footer, including checksum.
+	// The entire image size must be a multiple of 16, so pad the image to one
+	// byte less than that before writing the checksum.
+	outf.Write(make([]byte, 15-outf.Len()%16))
+	outf.WriteByte(checksum)
+
+	if chip != "esp8266" {
+		// SHA256 hash (to protect against image corruption, not for security).
+		hash := sha256.Sum256(outf.Bytes())
+		outf.Write(hash[:])
+	}
+
+	// QEMU (or more precisely, qemu-system-xtensa from Espressif) expects the
+	// image to be a certain size.
+	if makeImage {
+		// Use a default image size of 4MB.
+		grow := 4096*1024 - outf.Len()
+		if grow > 0 {
+			outf.Write(make([]byte, grow))
+		}
+	}
+
+	// Write the image to the output file.
+	return os.WriteFile(outfile, outf.Bytes(), 0666)
+}

internal/firmware/ext.go

@@ -0,0 +1,12 @@
+package firmware
+
+import "strings"
+
+// BinaryExt returns the binary file extension based on the binary format
+// Returns ".bin" for ESP-based formats, "" for others
+func BinaryExt(binaryFormat string) string {
+	if strings.HasPrefix(binaryFormat, "esp") {
+		return ".bin"
+	}
+	return ""
+}

internal/firmware/ext_test.go

@@ -0,0 +1,28 @@
+package firmware
+
+import "testing"
+
+func TestBinaryExt(t *testing.T) {
+	tests := []struct {
+		name         string
+		binaryFormat string
+		expected     string
+	}{
+		{"ESP32", "esp32", ".bin"},
+		{"ESP8266", "esp8266", ".bin"},
+		{"ESP32C3", "esp32c3", ".bin"},
+		{"UF2", "uf2", ""},
+		{"ELF", "elf", ""},
+		{"Empty", "", ""},
+		{"NRF-DFU", "nrf-dfu", ""},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			result := BinaryExt(tt.binaryFormat)
+			if result != tt.expected {
+				t.Errorf("BinaryExt() = %q, want %q", result, tt.expected)
+			}
+		})
+	}
+}

internal/firmware/firmware.go

@@ -0,0 +1,14 @@
+package firmware
+
+import (
+	"fmt"
+	"strings"
+)
+
+func MakeFirmwareImage(infile, outfile, format string) error {
+	fmt.Printf("Creating firmware image from %s to %s with format %s\n", infile, outfile, format)
+	if strings.HasPrefix(format, "esp") {
+		return makeESPFirmareImage(infile, outfile, format)
+	}
+	return fmt.Errorf("unsupported firmware format: %s", format)
+}

internal/targets/config.go

@@ -26,6 +26,33 @@ type Config struct {
 	CodeModel       string `json:"code-model"`
 	TargetABI       string `json:"target-abi"`
 	RelocationModel string `json:"relocation-model"`
+
+	// Binary and firmware configuration
+	BinaryFormat string `json:"binary-format"`
+
+	// Flash and deployment configuration
+	FlashCommand      string `json:"flash-command"`
+	FlashMethod       string `json:"flash-method"`
+	Flash1200BpsReset string `json:"flash-1200-bps-reset"`
+
+	// Mass storage device configuration
+	MSDVolumeName   []string `json:"msd-volume-name"`
+	MSDFirmwareName string   `json:"msd-firmware-name"`
+
+	// UF2 configuration
+	UF2FamilyID string `json:"uf2-family-id"`
+
+	// Device-specific configuration
+	RP2040BootPatch bool `json:"rp2040-boot-patch"`
+
+	// Debug and emulation configuration
+	Emulator string   `json:"emulator"`
+	GDB      []string `json:"gdb"`
+
+	// OpenOCD configuration
+	OpenOCDInterface string `json:"openocd-interface"`
+	OpenOCDTransport string `json:"openocd-transport"`
+	OpenOCDTarget    string `json:"openocd-target"`
 }
 
 // RawConfig represents the raw JSON configuration before inheritance resolution

internal/targets/loader.go

@@ -149,6 +149,39 @@ func (l *Loader) mergeConfig(dst, src *Config) {
 	if src.RelocationModel != "" {
 		dst.RelocationModel = src.RelocationModel
 	}
+	if src.BinaryFormat != "" {
+		dst.BinaryFormat = src.BinaryFormat
+	}
+	if src.FlashCommand != "" {
+		dst.FlashCommand = src.FlashCommand
+	}
+	if src.FlashMethod != "" {
+		dst.FlashMethod = src.FlashMethod
+	}
+	if src.Flash1200BpsReset != "" {
+		dst.Flash1200BpsReset = src.Flash1200BpsReset
+	}
+	if src.MSDFirmwareName != "" {
+		dst.MSDFirmwareName = src.MSDFirmwareName
+	}
+	if src.UF2FamilyID != "" {
+		dst.UF2FamilyID = src.UF2FamilyID
+	}
+	if src.RP2040BootPatch {
+		dst.RP2040BootPatch = src.RP2040BootPatch
+	}
+	if src.Emulator != "" {
+		dst.Emulator = src.Emulator
+	}
+	if src.OpenOCDInterface != "" {
+		dst.OpenOCDInterface = src.OpenOCDInterface
+	}
+	if src.OpenOCDTransport != "" {
+		dst.OpenOCDTransport = src.OpenOCDTransport
+	}
+	if src.OpenOCDTarget != "" {
+		dst.OpenOCDTarget = src.OpenOCDTarget
+	}
 
 	// Merge slices (append, don't replace)
 	if len(src.BuildTags) > 0 {
@@ -163,6 +196,12 @@ func (l *Loader) mergeConfig(dst, src *Config) {
 	if len(src.ExtraFiles) > 0 {
 		dst.ExtraFiles = append(dst.ExtraFiles, src.ExtraFiles...)
 	}
+	if len(src.MSDVolumeName) > 0 {
+		dst.MSDVolumeName = append(dst.MSDVolumeName, src.MSDVolumeName...)
+	}
+	if len(src.GDB) > 0 {
+		dst.GDB = append(dst.GDB, src.GDB...)
+	}
 }
 
 // GetTargetsDir returns the targets directory path

internal/targets/targets_test.go

@@ -61,7 +61,8 @@ func TestLoaderLoadRaw(t *testing.T) {
 		"goarch": "arm",
 		"build-tags": ["test", "embedded"],
 		"cflags": ["-Os", "-g"],
-		"ldflags": ["--gc-sections"]
+		"ldflags": ["--gc-sections"],
+		"binary-format": "uf2"
 	}`
 
 	configPath := filepath.Join(tempDir, "test-target.json")
@@ -87,6 +88,9 @@ func TestLoaderLoadRaw(t *testing.T) {
 	if len(config.BuildTags) != 2 || config.BuildTags[0] != "test" || config.BuildTags[1] != "embedded" {
 		t.Errorf("Expected build-tags [test, embedded], got %v", config.BuildTags)
 	}
+	if config.BinaryFormat != "uf2" {
+		t.Errorf("Expected binary-format 'uf2', got '%s'", config.BinaryFormat)
+	}
 }
 
 func TestLoaderInheritance(t *testing.T) {
@@ -99,7 +103,8 @@ func TestLoaderInheritance(t *testing.T) {
 		"goos": "linux",
 		"goarch": "arm",
 		"cflags": ["-Os"],
-		"ldflags": ["--gc-sections"]
+		"ldflags": ["--gc-sections"],
+		"binary-format": "elf"
 	}`
 
 	// Create child config that inherits from parent
@@ -108,7 +113,8 @@ func TestLoaderInheritance(t *testing.T) {
 		"cpu": "cortex-m4",
 		"build-tags": ["child"],
 		"cflags": ["-O2"],
-		"ldflags": ["-g"]
+		"ldflags": ["-g"],
+		"binary-format": "uf2"
 	}`
 
 	parentPath := filepath.Join(tempDir, "parent.json")
@@ -143,6 +149,11 @@ func TestLoaderInheritance(t *testing.T) {
 		t.Errorf("Expected overridden cpu 'cortex-m4', got '%s'", config.CPU)
 	}
 
+	// Check binary-format override
+	if config.BinaryFormat != "uf2" {
+		t.Errorf("Expected overridden binary-format 'uf2', got '%s'", config.BinaryFormat)
+	}
+
 	// Check merged arrays
 	expectedCFlags := []string{"-Os", "-O2"}
 	if len(config.CFlags) != 2 || config.CFlags[0] != "-Os" || config.CFlags[1] != "-O2" {