add documentation, smoke test and fix a couple bugs

sd/blockdevice.go

@@ -15,6 +15,9 @@ var _ Card = (*SPICard)(nil)
 var _ io.ReaderAt = (*BlockDevice)(nil)
 var _ io.WriterAt = (*BlockDevice)(nil)
 
+// Card is the interface implemented by SD card drivers such as [SPICard].
+// It provides block-aligned I/O over the card's contents. Use [NewBlockDevice]
+// to wrap a Card with byte-addressed [io.ReaderAt] and [io.WriterAt] interfaces.
 type Card interface {
 	// WriteBlocks writes the given data to the card, starting at the given block index.
 	// The data must be a multiple of the block size.
@@ -26,7 +29,9 @@ type Card interface {
 	EraseBlocks(startBlock, numBlocks int64) error
 }
 
-// NewBlockDevice creates a new BlockDevice from a Card.
+// NewBlockDevice creates a new [BlockDevice] from a Card. blockSize must be a
+// power of 2. For an initialized [SPICard], blockSize is typically the CSD's
+// [CSD.ReadBlockLen] and numBlocks is [SPICard.NumberOfBlocks].
 func NewBlockDevice(card Card, blockSize int, numBlocks int64) (*BlockDevice, error) {
 	if card == nil || blockSize <= 0 || numBlocks <= 0 {
 		return nil, errors.New("invalid argument(s)")
@@ -44,7 +49,10 @@ func NewBlockDevice(card Card, blockSize int, numBlocks int64) (*BlockDevice, er
 	return bd, nil
 }
 
-// BlockDevice implements tinyfs.BlockDevice interface for an [sd.Card] type.
+// BlockDevice implements the tinyfs.BlockDevice interface for a [Card],
+// providing byte-addressed reads and writes at arbitrary offsets by buffering
+// non-block-aligned accesses through an internal single-block buffer.
+// BlockDevice is not safe for concurrent use.
 type BlockDevice struct {
 	card      Card
 	blockbuf  []byte
@@ -52,7 +60,8 @@ type BlockDevice struct {
 	numblocks int64
 }
 
-// ReadAt implements [io.ReadAt] interface for an SD card.
+// ReadAt implements the [io.ReaderAt] interface for an SD card.
+// Reads need not be aligned to block boundaries.
 func (bd *BlockDevice) ReadAt(p []byte, off int64) (n int, err error) {
 	if off < 0 {
 		return 0, errNegativeOffset
@@ -93,7 +102,9 @@ func (bd *BlockDevice) ReadAt(p []byte, off int64) (n int, err error) {
 	return n, nil
 }
 
-// WriteAt implements [io.WriterAt] interface for an SD card.
+// WriteAt implements the [io.WriterAt] interface for an SD card. Writes need
+// not be aligned to block boundaries: partial blocks are read, modified and
+// written back.
 func (bd *BlockDevice) WriteAt(p []byte, off int64) (n int, err error) {
 	if off < 0 {
 		return 0, errNegativeOffset
@@ -174,6 +185,8 @@ type blkIdxer struct {
 	blockmask  int64
 }
 
+// makeBlockIndexer returns a blkIdxer for the given block size,
+// which must be a power of 2.
 func makeBlockIndexer(blockSize int) (blkIdxer, error) {
 	if blockSize <= 0 {
 		return blkIdxer{}, errNoblocks

sd/card_test.go

@@ -85,6 +85,89 @@ func TestCRC7(t *testing.T) {
 	}
 }
 
+// TestCSDv2Capacity checks CSDv2 C_SIZE decoding and the capacity formula.
+//
+// Field layout and formula are from the SD Physical Layer Simplified
+// Specification Version 9.10, section 5.3.3 "CSD Register (CSD Version 2.0)":
+// C_SIZE occupies CSD bits [69:48] and user memory capacity is
+//
+//	memory capacity = (C_SIZE+1) * 512KByte  (512KByte = 524288 bytes)
+//
+// Specification download: https://www.sdcard.org/downloads/pls/
+//
+// Regression test for two past bugs in CSDv2:
+//   - csize() read byte 7 as data[7]>>2 instead of data[7]&0x3F, dropping
+//     C_SIZE bits [17:16] (misdecoded cards > 32GiB).
+//   - DeviceCapacity() computed csize*512000 instead of (csize+1)*524288.
+func TestCSDv2Capacity(t *testing.T) {
+	tests := []struct {
+		name      string
+		csd       []byte
+		wantCSize uint32
+		wantCap   int64
+	}{
+		{
+			// Same 8GB-card register as in TestCRC7 above, CRC byte appended
+			// (CRC7=0b1110010 per that test, stored as crc<<1|always1).
+			// C_SIZE = 0x003C01 = 15361 -> 15362 * 524288 = 8054112256 bytes.
+			name:      "8GB card (in-repo vector)",
+			csd:       []byte{64, 14, 0, 50, 83, 89, 0, 0, 60, 1, 127, 128, 10, 64, 0, 0b1110010<<1 | 1},
+			wantCSize: 0x003C01,
+			wantCap:   8054112256,
+		},
+		// {
+		// 	name:      "8GB card",
+		// 	csd:       csdv2Bytes(0x003C01),
+		// 	wantCSize: 0x003FFF,
+		// 	wantCap:   2 << 40,
+		// },
+		{
+			// Synthetic: C_SIZE = 0x01FFFF -> 131072 * 524288 = 64GiB.
+			// Exercises C_SIZE bits [17:16], stored in CSD byte 7 (CSD bits [65:64]).
+			name:      "64GiB synthetic",
+			csd:       csdv2Bytes(0x01FFFF),
+			wantCSize: 0x01FFFF,
+			wantCap:   64 << 30,
+		},
+		{
+			// Synthetic: maximum v2 C_SIZE = 0x3FFFFF -> 4194304 * 524288 = 2TiB,
+			// the SDXC upper bound per section 5.3.3.
+			name:      "2TiB synthetic (max C_SIZE)",
+			csd:       csdv2Bytes(0x3FFFFF),
+			wantCSize: 0x3FFFFF,
+			wantCap:   2 << 40,
+		},
+	}
+	for _, tt := range tests {
+		csd, err := DecodeCSD(tt.csd)
+		if err != nil {
+			t.Fatalf("%s: DecodeCSD: %v", tt.name, err)
+		}
+		v2 := csd.MustV2()
+		if got := v2.csize(); got != tt.wantCSize {
+			t.Errorf("%s: csize() = %#x, want %#x", tt.name, got, tt.wantCSize)
+		}
+		if got := csd.DeviceCapacity(); got != tt.wantCap {
+			t.Errorf("%s: DeviceCapacity() = %d, want %d", tt.name, got, tt.wantCap)
+		}
+		wantBlocks := tt.wantCap / int64(csd.ReadBlockLen())
+		if got := csd.NumberOfBlocks(); got != wantBlocks {
+			t.Errorf("%s: NumberOfBlocks() = %d, want %d", tt.name, got, wantBlocks)
+		}
+	}
+}
+
+// csdv2Bytes returns a 16-byte CSD v2 register with csize spliced into
+// CSD bits [69:48] and a freshly computed CRC7+always1 last byte.
+// Non-capacity fields are copied from the 8GB-card vector above.
+func csdv2Bytes(csize uint32) []byte {
+	b := []byte{64, 14, 0, 50, 83, 89, 0, 0, 60, 1, 127, 128, 10, 64, 0}
+	b[7] = byte(csize >> 16 & 0x3F)
+	b[8] = byte(csize >> 8)
+	b[9] = byte(csize)
+	return append(b, crc7noshift(b)|1)
+}
+
 func putCmd(dst []byte, cmd command, arg uint32) {
 	dst[0] = byte(cmd) | (1 << 6)
 	dst[1] = byte(arg >> 24)

sd/definitions.go

@@ -11,8 +11,11 @@ import (
 // For reference of CID/CSD structs see:
 // See https://github.com/arduino-libraries/SD/blob/1c56f58252553c7537f7baf62798cacc625aa543/src/utility/SdInfo.h#L110
 
+// CardKind classifies an SD card by its capacity class and specification
+// version, as discovered during card initialization.
 type CardKind uint8
 
+// isTimeout reports whether err is one of the package's timeout errors.
 func isTimeout(err error) bool {
 	return err == errReadTimeout || err == errWriteTimeout || err == errBusyTimeout
 }
@@ -24,10 +27,16 @@ const (
 	TypeSDHC CardKind = 3 // High Capacity SD card
 )
 
+// CID is the Card Identification register, a 128-bit (16-byte) read-only
+// register holding the card's identification information: manufacturer,
+// product name, serial number and manufacturing date, among other data.
+// It is programmed during card manufacture and cannot be changed.
 type CID struct {
 	data [16]byte
 }
 
+// DecodeCID decodes a CID from the first 16 bytes of b. It returns an error
+// if b is too short or if the CRC7/always-1 fields are invalid.
 func DecodeCID(b []byte) (cid CID, _ error) {
 	if len(b) < 16 {
 		return CID{}, io.ErrShortBuffer
@@ -52,7 +61,7 @@ func (c *CID) OEMApplicationID() uint16 {
 	return binary.BigEndian.Uint16(c.data[1:3])
 }
 
-// The product name is a string, 5-character ASCII string.
+// ProductName returns the product name, an ASCII string of up to 5 characters.
 func (c *CID) ProductName() string {
 	return string(upToNull(c.data[3:8]))
 }
@@ -65,12 +74,13 @@ func (c *CID) ProductRevision() (n, m uint8) {
 	return rev >> 4, rev & 0x0F
 }
 
-// The Serial Number is 32 bits of binary number.
+// ProductSerialNumber returns the product serial number, a 32-bit binary number.
 func (c *CID) ProductSerialNumber() uint32 {
 	return binary.BigEndian.Uint32(c.data[9:13])
 }
 
-// ManufacturingDate returns the manufacturing date of the card.
+// ManufacturingDate returns the manufacturing date of the card,
+// e.g. year=2023, month=4 for April 2023.
 func (c *CID) ManufacturingDate() (year uint16, month uint8) {
 	date := binary.BigEndian.Uint16(c.data[13:15])
 	return (date >> 4) + 2000, uint8(date & 0x0F)
@@ -129,6 +139,7 @@ func (c CSD) MustV1() CSDv1 {
 	return CSDv1{CSD: c}
 }
 
+// MustV2 returns the CSD as a CSDv2. Panics if the CSD is not version 2.0.
 func (c CSD) MustV2() CSDv2 {
 	if c.csdStructure() != 1 {
 		panic("CSD is not version 2.0")
@@ -136,6 +147,7 @@ func (c CSD) MustV2() CSDv2 {
 	return CSDv2{CSD: c}
 }
 
+// RawCopy returns a copy of the raw CSD data.
 func (c *CSD) RawCopy() [16]byte { return c.data }
 
 // TAAC returns the Time Access Attribute Class (data read access-time-1).
@@ -147,17 +159,20 @@ func (c *CSD) NSAC() NSAC { return NSAC(c.data[2]) }
 // TransferSpeed returns the Max Data Transfer Rate. Either 0x32 or 0x5A.
 func (c *CSD) TransferSpeed() TransferSpeed { return TransferSpeed(c.data[3]) }
 
-// CommandClasses returns the supported Card Command Classes.
+// CommandClasses returns the supported Card Command Classes as a bitfield;
-// This is a bitfield, each bit position indicates whether the
+// bit position i set means command class i is supported by the card.
 func (c *CSD) CommandClasses() CommandClasses {
 	return CommandClasses(uint16(c.data[4])<<4 | uint16(c.data[5]&0xf0)>>4)
 }
 
 // ReadBlockLen returns the Max Read Data Block Length in bytes.
-func (c *CSD) ReadBlockLen() int        { return 1 << c.ReadBlockLenShift() }
+func (c *CSD) ReadBlockLen() int { return 1 << c.ReadBlockLenShift() }
+
+// ReadBlockLenShift returns the base-2 logarithm of [CSD.ReadBlockLen] (READ_BL_LEN field).
 func (c *CSD) ReadBlockLenShift() uint8 { return c.data[5] & 0x0F }
 
-// AllowsReadBlockPartial should always return true. Indicates that
+// AllowsReadBlockPartial indicates that partial block reads (down to a
+// single byte) are allowed. Always true for SD cards.
 func (c *CSD) AllowsReadBlockPartial() bool { return c.data[6]&(1<<7) != 0 }
 
 // AllowsWriteBlockMisalignment defines if the data block to be written by one command
@@ -183,15 +198,18 @@ func (c *CSD) IsValid() bool {
 // ImplementsDSR defines if the configurable driver stage is integrated on the card.
 func (c *CSD) ImplementsDSR() bool { return c.data[6]&(1<<4) != 0 }
 
-// EraseSectorSizeInBlocks represents how much memory is erased in an erase
+// EraseSectorSizeInBytes returns how much memory is erased by a single
-// command in multiple of block size.
+// erase command, in bytes (SectorSize multiplied by the write block length).
 func (c *CSDv1) EraseSectorSizeInBytes() int64 {
 	blklen := c.WriteBlockLen()
 	numblocks := c.SectorSize()
 	return int64(numblocks) * blklen
 }
 
-// SectorSize varies in meaning depending on the version.
+// SectorSize returns the size of an erasable sector in units of write blocks
+// (SECTOR_SIZE field, range 1..128). Its meaning varies with the CSD version:
+// for V1 it is the erase unit when [CSD.EraseBlockEnabled] is false; for V2
+// it is fixed to 64KiB and does not reflect the real erase unit.
 func (c *CSD) SectorSize() uint8 {
 	return 1 + ((c.data[10]&0b11_1111)<<1 | (c.data[11] >> 7))
 }
@@ -200,6 +218,8 @@ func (c *CSD) SectorSize() uint8 {
 // If enabled the erase operation can erase either one or multiple units of 512 bytes.
 func (c *CSD) EraseBlockEnabled() bool { return (c.data[10]>>6)&1 != 0 }
 
+// ReadToWriteFactor returns the typical write time as a power-of-2 multiple of
+// the read access time (R2W_FACTOR field), i.e. writeTime = readTime << factor.
 func (c *CSD) ReadToWriteFactor() uint8 { return (c.data[12] >> 2) & 0b111 }
 
 // WriteProtectGroupSizeInSectors indicates the size of a write protected
@@ -231,8 +251,12 @@ func (c *CSD) PermWriteProtected() bool { return c.data[14]&(1<<5) != 0 }
 // IsCopy whether contents are original or have been copied.
 func (c *CSD) IsCopy() bool { return c.data[14]&(1<<6) != 0 }
 
+// FileFormatGroup returns the file format group bit, which selects between
+// the two [FileFormat] tables. Interpret together with [CSD.FileFormat].
 func (c *CSD) FileFormatGroup() bool { return c.data[14]&(1<<7) != 0 }
 
+// DeviceCapacity returns the total device capacity in bytes, dispatching on
+// the CSD version. Returns 0 for unknown CSD versions.
 func (c *CSD) DeviceCapacity() (size int64) {
 	switch c.csdStructure() {
 	case 0:
@@ -256,14 +280,16 @@ func (c *CSD) NumberOfBlocks() (numBlocks int64) {
 
 // After byte 5 CSDv1 and CSDv2  differ in structure at some fields.
 
-// DeviceCapacity returns the device capacity in bytes.
+// DeviceCapacity returns the device capacity in bytes:
+// (C_SIZE+1) * 512KiB, as per section 5.3.3 of the SD Simplified Specification.
 func (c *CSDv2) DeviceCapacity() int64 {
 	csize := c.csize()
-	return int64(csize) * 512_000
+	return (int64(csize) + 1) * (512 * 1024)
 }
 
+// csize returns the 22-bit C_SIZE field (CSD bits 69:48).
 func (c *CSDv2) csize() uint32 {
-	return uint32(c.data[7]>>2)<<16 | uint32(c.data[8])<<8 | uint32(c.data[9])
+	return uint32(c.data[7]&0x3F)<<16 | uint32(c.data[8])<<8 | uint32(c.data[9])
 }
 
 // DeviceCapacity returns the total memory capacity of the SDCard in bytes. Max is 2GB for V1.
@@ -301,6 +327,7 @@ func (c *CSDv1) VddWriteCurrent() (min, max uint8) {
 	return c.data[9] >> 5, (c.data[9] >> 3) & 0b111
 }
 
+// String returns a human-readable multi-line summary of the CSD fields.
 func (c *CSD) String() string {
 	version := c.csdStructure() + 1
 	if version > 2 {
@@ -424,13 +451,23 @@ const (
 	acmdCHANGE_SECURE_AREA       appcommand = 49
 )
 
-// CSD enum types.
+// CSD field types.
 type (
-	TransferSpeed  uint8
+	// TransferSpeed is the TRAN_SPEED CSD field: the maximum data transfer
-	TAAC           uint8
+	// rate encoded as a rate unit (lower 3 bits) and time value multiplier.
-	FileFormat     uint8
+	TransferSpeed uint8
+	// TAAC is the data read access time CSD field, encoded as a time unit
+	// (lower 3 bits) and time value multiplier.
+	TAAC uint8
+	// FileFormat is the format of the data stored on the card. See the
+	// FileFmt* constants for possible values.
+	FileFormat uint8
+	// CommandClasses is the CCC CSD field, a bitfield where bit position i
+	// set means command class i is supported.
 	CommandClasses uint16
-	NSAC           uint8
+	// NSAC is the data read access time 2 CSD field, given in units of
+	// 100 clock cycles.
+	NSAC uint8
 )
 
 const (
@@ -440,6 +477,7 @@ const (
 	FileFmtUnknown
 )
 
+// String returns a human-readable name for the file format.
 func (ff FileFormat) String() (s string) {
 	switch ff {
 	case FileFmtPartition:
@@ -466,11 +504,12 @@ var log10table = [...]int64{
 	1000000,
 }
 
-// RateMegabits returns the transfer rate in kilobits per second.
+// RateKilobits returns the transfer rate in kilobits per second.
 func (t TransferSpeed) RateKilobits() int64 {
 	return 100 * log10table[t&0b111]
 }
 
+// AccessTime returns the asynchronous part of the data access time.
 func (t TAAC) AccessTime() (d time.Duration) {
 	return time.Duration(log10table[t&0b111]) * time.Nanosecond
 }

sd/doc.go

@@ -0,0 +1,8 @@
+// Package sd implements SD card drivers and the SD card specification:
+// CID and CSD register decoding, command definitions and CRC7/CRC16 checksums.
+//
+// The [SPICard] type drives an SD card over a SPI bus and implements the
+// [Card] interface, which exposes block-aligned I/O. [BlockDevice] wraps any
+// [Card] with byte-addressed [io.ReaderAt]/[io.WriterAt] implementations
+// suitable for filesystem libraries such as tinyfs.
+package sd

sd/responses.go

@@ -2,7 +2,6 @@ package sd
 
 import (
 	"encoding/binary"
-	"strconv"
 )
 
 const (
@@ -20,6 +19,8 @@ const (
 	_DATA_RES_ACCEPTED = 0x05
 )
 
+// response1 is the R1 response token returned by the card in SPI mode
+// after every command; a bitfield of error and idle-state flags.
 type response1 uint8
 
 func (r response1) IsIdle() bool          { return r&_R1_IDLE_STATE != 0 }
@@ -30,17 +31,17 @@ func (r response1) EraseSeqError() bool   { return r&_R1_ERASE_SEQUENCE_ERROR !=
 func (r response1) AddressError() bool    { return r&_R1_ADDRESS_ERROR != 0 }
 func (r response1) ParamError() bool      { return r&_R1_PARAMETER_ERROR != 0 }
 
+// response1Err wraps a non-zero response1 status as an error.
 type response1Err struct {
 	context string
 	status  response1
 }
 
 func (e response1Err) Error() string {
-	return e.status.Response()
 	if e.context != "" {
-		return "sd:" + e.context + " " + strconv.Itoa(int(e.status))
+		return "sd:" + e.context + " " + e.status.Response()
 	}
-	return "sd:status " + strconv.Itoa(int(e.status))
+	return e.status.Response()
 }
 
 func (e response1) Response() string {
@@ -96,6 +97,8 @@ const (
 	tokWRITE_MULT  = 0xfc
 )
 
+// state is the card state machine state as encoded in the
+// CURRENT_STATE bits of the Card Status register (section 4.10.1).
 type state uint8
 
 const (
@@ -153,7 +156,8 @@ const (
 	statusAddrOutOfRange  // address out of range
 )
 
-// r1 is the normal response to a command.
+// r1 is the normal 48-bit response to a command in SD-bus mode,
+// as per section 4.9.1. It carries the 32-bit Card Status register.
 type r1 struct {
 	data [48 / 8]byte // 48 bits of response.
 }
@@ -178,6 +182,8 @@ func (r *r1) IsValid() bool {
 	return r.endbit() && CRC7(r.data[:5]) == r.CRC7()
 }
 
+// r6 is the 48-bit Published RCA response, as per section 4.9.5. It carries
+// the card's new Relative Card Address and a subset of the Card Status bits.
 type r6 struct {
 	data [48 / 8]byte
 }

sd/spicard.go

@@ -10,8 +10,6 @@ import (
 	"tinygo.org/x/drivers"
 )
 
-// See rustref.go for the new implementation.
-
 var (
 	errBadCSDCID            = errors.New("sd:bad CSD/CID in CRC or always1")
 	errNoSDCard             = errors.New("sd:no card")
@@ -26,8 +24,12 @@ var (
 	errNoblocks             = errors.New("sd:no readable blocks")
 )
 
+// digitalPinout sets the logic level of an output pin; true for high, false for low.
 type digitalPinout = func(b bool)
 
+// SPICard is a SPI-mode SD card driver. It implements the [Card] interface
+// and is initialized with [NewSPICard] followed by a call to [SPICard.Init].
+// SPICard is not safe for concurrent use.
 type SPICard struct {
 	bus drivers.SPI
 	cs  digitalPinout
@@ -46,6 +48,9 @@ type SPICard struct {
 	lastCRC uint16
 }
 
+// NewSPICard returns a new [SPICard] that communicates over spi using cs as
+// the chip select pin. The returned card must be initialized with [SPICard.Init]
+// before use.
 func NewSPICard(spi drivers.SPI, cs digitalPinout) *SPICard {
 	const defaultTimeout = 300 * time.Millisecond
 	s := &SPICard{
@@ -74,6 +79,8 @@ func (d *SPICard) Init() error {
 	return d.initRs()
 }
 
+// NumberOfBlocks returns the number of readable and writable blocks on the card,
+// as calculated from the CSD read during [SPICard.Init].
 func (d *SPICard) NumberOfBlocks() int64 {
 	return d.csd.NumberOfBlocks()
 }
@@ -233,7 +240,9 @@ func (d *SPICard) updateCSDCID() (err error) {
 	return nil
 }
 
-// ReadBlock reads to a buffer multiple of 512 bytes from sdcard into dst starting at block `startBlockIdx`.
+// ReadBlocks reads card data into dst beginning at the block index startBlockIdx.
+// len(dst) must be a multiple of the card's block size (see [CSD.ReadBlockLen]).
+// It returns the number of bytes read into dst and any error encountered.
 func (d *SPICard) ReadBlocks(dst []byte, startBlockIdx int64) (int, error) {
 	numblocks, err := d.checkBounds(startBlockIdx, len(dst))
 	if err != nil {
@@ -267,11 +276,15 @@ func (d *SPICard) ReadBlocks(dst []byte, startBlockIdx int64) (int, error) {
 	panic("unreachable numblocks<=0")
 }
 
+// EraseBlocks erases numberOfBlocks blocks beginning at startBlock.
+// It always returns an error since erase is not yet implemented for SPICard.
 func (d *SPICard) EraseBlocks(startBlock, numberOfBlocks int64) error {
 	return errors.New("sd:erase not implemented")
 }
 
-// WriteBlocks writes to sdcard from a buffer multiple of 512 bytes from src starting at block `startBlockIdx`.
+// WriteBlocks writes data to the card beginning at the block index startBlockIdx.
+// len(data) must be a multiple of the card's block size (see [CSD.WriteBlockLen]).
+// It returns the number of bytes written and any error encountered.
 func (d *SPICard) WriteBlocks(data []byte, startBlockIdx int64) (int, error) {
 	numblocks, err := d.checkBounds(startBlockIdx, len(data))
 	if err != nil {

smoketest.sh

@@ -129,6 +129,7 @@ tinygo build -size short -o ./build/test.hex -target=microbit ./examples/ndir/ma
 tinygo build -size short -o ./build/test.hex -target=arduino-nano33 ./examples/ndir/main_ndir.go
 tinygo build -size short -o ./build/test.uf2 -target=pico ./examples/mpu9150/main.go
 tinygo build -size short -o ./build/test.hex -target=macropad-rp2040 ./examples/sh1106/macropad_spi
+tinygo build -size short -o ./build/test.hex -target=pico ./examples/sd
 # network examples (espat)
 tinygo build -size short -o ./build/test.hex -target=challenger-rp2040 ./examples/net/ntpclient/
 # network examples (wifinina)