xiao-esp32s3
Constants
const (
D0 = GPIO1
D1 = GPIO2
D2 = GPIO3
D3 = GPIO4
D4 = GPIO5
D5 = GPIO6
D6 = GPIO43
D7 = GPIO44
D8 = GPIO7
D9 = GPIO8
D10 = GPIO9
)
Digital Pins
const (
A0 = GPIO1
A1 = GPIO2
A2 = GPIO3
A3 = GPIO4
)
Analog pins
const (
UART_RX_PIN = GPIO44
UART_TX_PIN = GPIO43
)
UART pins
const (
SDA_PIN = GPIO5
SCL_PIN = GPIO6
)
I2C pins
const (
SPI1_SCK_PIN = GPIO7 // D8
SPI1_MISO_PIN = GPIO8 // D9
SPI1_MOSI_PIN = GPIO9 // D10
SPI1_CS_PIN = NoPin
SPI2_SCK_PIN = NoPin
SPI2_MOSI_PIN = NoPin
SPI2_MISO_PIN = NoPin
SPI2_CS_PIN = NoPin
)
SPI pins
const (
LED = GPIO21
)
Onboard LEDs
const (
TWI_FREQ_100KHZ = 100000
TWI_FREQ_400KHZ = 400000
)
TWI_FREQ is the I2C bus speed. Normally either 100 kHz, or 400 kHz for high-speed bus.
Deprecated: use 100 * machine.KHz or 400 * machine.KHz instead.
const (
// I2CReceive indicates target has received a message from the controller.
I2CReceive I2CTargetEvent = iota
// I2CRequest indicates the controller is expecting a message from the target.
I2CRequest
// I2CFinish indicates the controller has ended the transaction.
//
// I2C controllers can chain multiple receive/request messages without
// relinquishing the bus by doing 'restarts'. I2CFinish indicates the
// bus has been relinquished by an I2C 'stop'.
I2CFinish
)
const (
// I2CModeController represents an I2C peripheral in controller mode.
I2CModeController I2CMode = iota
// I2CModeTarget represents an I2C peripheral in target mode.
I2CModeTarget
)
const Device = deviceName
Device is the running program’s chip name, such as “ATSAMD51J19A” or “nrf52840”. It is not the same as the CPU name.
The constant is some hardcoded default value if the program does not target a particular chip but instead runs in WebAssembly for example.
const (
KHz = 1000
MHz = 1000_000
GHz = 1000_000_000
)
Generic constants.
const NoPin = Pin(0xff)
NoPin explicitly indicates “not a pin”. Use this pin if you want to leave one of the pins in a peripheral unconfigured (if supported by the hardware).
const (
PinOutput PinMode = iota
PinInput
PinInputPullup
PinInputPulldown
PinAnalog
)
const (
GPIO0 Pin = 0
GPIO1 Pin = 1
GPIO2 Pin = 2
GPIO3 Pin = 3
GPIO4 Pin = 4
GPIO5 Pin = 5
GPIO6 Pin = 6
GPIO7 Pin = 7
GPIO8 Pin = 8
GPIO9 Pin = 9
GPIO10 Pin = 10
GPIO11 Pin = 11
GPIO12 Pin = 12
GPIO13 Pin = 13
GPIO14 Pin = 14
GPIO15 Pin = 15
GPIO16 Pin = 16
GPIO17 Pin = 17
GPIO18 Pin = 18
GPIO19 Pin = 19
GPIO20 Pin = 20
GPIO21 Pin = 21
GPIO26 Pin = 26
GPIO27 Pin = 27
GPIO28 Pin = 28
GPIO29 Pin = 29
GPIO30 Pin = 30
GPIO31 Pin = 31
GPIO32 Pin = 32
GPIO33 Pin = 33
GPIO34 Pin = 34
GPIO35 Pin = 35
GPIO36 Pin = 36
GPIO37 Pin = 37
GPIO38 Pin = 38
GPIO39 Pin = 39
GPIO40 Pin = 40
GPIO41 Pin = 41
GPIO42 Pin = 42
GPIO43 Pin = 43
GPIO44 Pin = 44
GPIO45 Pin = 45
GPIO46 Pin = 46
GPIO47 Pin = 47
GPIO48 Pin = 48
)
Hardware pin numbers
const (
ADC0 Pin = GPIO1
ADC2 Pin = GPIO2
ADC3 Pin = GPIO3
ADC4 Pin = GPIO4
ADC5 Pin = GPIO5
ADC6 Pin = GPIO6
ADC7 Pin = GPIO7
ADC8 Pin = GPIO8
ADC9 Pin = GPIO9
ADC10 Pin = GPIO10
ADC11 Pin = GPIO11
ADC12 Pin = GPIO12
ADC13 Pin = GPIO13
ADC14 Pin = GPIO14
ADC15 Pin = GPIO15
ADC16 Pin = GPIO16
ADC17 Pin = GPIO17
ADC18 Pin = GPIO18
ADC19 Pin = GPIO19
ADC20 Pin = GPIO20
)
const (
PinRising PinChange = iota + 1
PinFalling
PinToggle
)
Pin change interrupt constants for SetInterrupt.
const (
I2CEXT0_SCL_OUT_IDX = 89
I2CEXT0_SDA_OUT_IDX = 90
I2CEXT1_SCL_OUT_IDX = 91
I2CEXT1_SDA_OUT_IDX = 92
)
const (
LEDC_LS_SIG_OUT0_IDX = 73
)
GPIO matrix output signal indices for LEDC (soc/gpio_sig_map.h)
const (
// ESP32-S3 PLL clock frequency (same as ESP32-C3)
pplClockFreq = 80e6
// Default SPI frequency - maximum safe speed
SPI_DEFAULT_FREQUENCY = 80e6 // 80MHz
)
const (
// IO MUX function number for SPI direct connection
SPI_IOMUX_FUNC = 4
)
const (
// SPI2 (FSPI) signals - Hardware SPI2 - CORRECT VALUES from ESP-IDF
SPI2_CLK_OUT_IDX = uint32(101) // FSPICLK_OUT_IDX
SPI2_CLK_IN_IDX = uint32(101) // FSPICLK_IN_IDX
SPI2_Q_OUT_IDX = uint32(102) // FSPIQ_OUT_IDX (MISO)
SPI2_Q_IN_IDX = uint32(102) // FSPIQ_IN_IDX
SPI2_D_OUT_IDX = uint32(103) // FSPID_OUT_IDX (MOSI)
SPI2_D_IN_IDX = uint32(103) // FSPID_IN_IDX
SPI2_CS0_OUT_IDX = uint32(110) // FSPICS0_OUT_IDX
// SPI3 (HSPI) signals - Hardware SPI3 - CORRECTED from ESP-IDF gpio_sig_map.h
// Source: /esp-idf/components/soc/esp32s3/include/soc/gpio_sig_map.h
SPI3_CLK_OUT_IDX = uint32(66) // Line 136: SPI3_CLK_OUT_IDX
SPI3_CLK_IN_IDX = uint32(66) // Line 135: SPI3_CLK_IN_IDX
SPI3_Q_OUT_IDX = uint32(67) // Line 138: SPI3_Q_OUT_IDX (MISO)
SPI3_Q_IN_IDX = uint32(67) // Line 137: SPI3_Q_IN_IDX
SPI3_D_OUT_IDX = uint32(68) // Line 140: SPI3_D_OUT_IDX (MOSI)
SPI3_D_IN_IDX = uint32(68) // Line 139: SPI3_D_IN_IDX
SPI3_CS0_OUT_IDX = uint32(71) // Line 146: SPI3_CS0_OUT_IDX
)
ESP32-S3 GPIO Matrix signal indices for SPI - CORRECTED from ESP-IDF gpio_sig_map.h
const (
Mode0 = 0
Mode1 = 1
Mode2 = 2
Mode3 = 3
)
SPI phase and polarity configs CPOL and CPHA
const (
// ParityNone means to not use any parity checking. This is
// the most common setting.
ParityNone UARTParity = iota
// ParityEven means to expect that the total number of 1 bits sent
// should be an even number.
ParityEven
// ParityOdd means to expect that the total number of 1 bits sent
// should be an odd number.
ParityOdd
)
Variables
var (
ErrTimeoutRNG = errors.New("machine: RNG Timeout")
ErrClockRNG = errors.New("machine: RNG Clock Error")
ErrSeedRNG = errors.New("machine: RNG Seed Error")
ErrInvalidInputPin = errors.New("machine: invalid input pin")
ErrInvalidOutputPin = errors.New("machine: invalid output pin")
ErrInvalidClockPin = errors.New("machine: invalid clock pin")
ErrInvalidDataPin = errors.New("machine: invalid data pin")
ErrNoPinChangeChannel = errors.New("machine: no channel available for pin interrupt")
)
var (
ErrInvalidSPIBus = errors.New("machine: invalid SPI bus")
)
var DefaultUART = UART0
var (
UART0 = &_UART0
_UART0 = UART{Bus: esp.UART0, Buffer: NewRingBuffer()}
UART1 = &_UART1
_UART1 = UART{Bus: esp.UART1, Buffer: NewRingBuffer()}
UART2 = &_UART2
_UART2 = UART{Bus: esp.UART2, Buffer: NewRingBuffer()}
)
var (
I2C0 = &I2C{
Bus: esp.I2C0,
funcSCL: I2CEXT0_SCL_OUT_IDX,
funcSDA: I2CEXT0_SDA_OUT_IDX,
useExt1: false,
}
I2C1 = &I2C{
Bus: esp.I2C1,
funcSCL: I2CEXT1_SCL_OUT_IDX,
funcSDA: I2CEXT1_SDA_OUT_IDX,
useExt1: true,
}
)
var (
PWM0 = &LEDCPWM{SigOutBase: LEDC_LS_SIG_OUT0_IDX, NumChannels: ledcChannelsS3, timerNum: 0}
PWM1 = &LEDCPWM{SigOutBase: LEDC_LS_SIG_OUT0_IDX, NumChannels: ledcChannelsS3, timerNum: 1}
PWM2 = &LEDCPWM{SigOutBase: LEDC_LS_SIG_OUT0_IDX, NumChannels: ledcChannelsS3, timerNum: 2}
PWM3 = &LEDCPWM{SigOutBase: LEDC_LS_SIG_OUT0_IDX, NumChannels: ledcChannelsS3, timerNum: 3}
)
var (
SPI0 = &SPI{Bus: esp.SPI2, busID: 2} // Primary SPI (FSPI)
SPI1 = &SPI{Bus: esp.SPI3, busID: 3} // Secondary SPI (HSPI)
)
var (
_USBCDC = &USB_DEVICE{
Bus: esp.USB_DEVICE,
Buffer: NewRingBuffer(),
}
USBCDC Serialer = _USBCDC
)
var USBDev = &USBDevice{}
var (
ErrPWMPeriodTooLong = errors.New("pwm: period too long")
)
var Serial Serialer
Serial is implemented via USB (USB-CDC).
var (
ErrTxInvalidSliceSize = errors.New("SPI write and read slices must be same size")
errSPIInvalidMachineConfig = errors.New("SPI port was not configured properly by the machine")
)
func ConfigureUSBEndpoint
func ConfigureUSBEndpoint(desc descriptor.Descriptor, epSettings []usb.EndpointConfig, setup []usb.SetupConfig)
ConfigureUSBEndpoint is a no-op on ESP32-S3.
func FlushSerial
func FlushSerial()
FlushSerial flushes any pending USB serial TX data. Called from the runtime (e.g. before sleeping) to ensure data from print() without a trailing newline gets sent promptly.
func GetCPUFrequency
func GetCPUFrequency() (uint32, error)
GetCPUFrequency returns the current CPU frequency of the chip.
func GetRNG
func GetRNG() (ret uint32, err error)
GetRNG returns 32-bit random numbers using the ESP32-S3 true random number generator, Random numbers are generated based on the thermal noise in the system and the asynchronous clock mismatch. For maximum entropy also make sure that the SAR_ADC is enabled. See esp32-s3_technical_reference_manual_en.pdf p.920
func InitADC
func InitADC()
func InitSerial
func InitSerial()
func NewRingBuffer
func NewRingBuffer() *RingBuffer
NewRingBuffer returns a new ring buffer.
func SendUSBInPacket
func SendUSBInPacket(ep uint32, data []byte) bool
SendUSBInPacket is a no-op on ESP32-S3.
func SendZlp
func SendZlp()
SendZlp is a no-op on ESP32-S3.
func SetCPUFrequency
func SetCPUFrequency(frequency uint32) error
SetCPUFrequency sets the frequency of the CPU to one of several targets
type ADC
type ADC struct {
Pin Pin
}
func (ADC) Configure
func (a ADC) Configure(config ADCConfig) error
func (ADC) Get
func (a ADC) Get() uint16
func (ADC) GetVoltage
func (a ADC) GetVoltage() (raw uint32, v float64)
type ADCConfig
type ADCConfig struct {
Reference uint32 // analog reference voltage (AREF) in millivolts
Resolution uint32 // number of bits for a single conversion (e.g., 8, 10, 12)
Samples uint32 // number of samples for a single conversion (e.g., 4, 8, 16, 32)
SampleTime uint32 // sample time, in microseconds (µs)
}
ADCConfig holds ADC configuration parameters. If left unspecified, the zero value of each parameter will use the peripheral’s default settings.
type I2C
type I2C struct {
Bus *esp.I2C_Type
funcSCL, funcSDA uint32
useExt1 bool
txCmdBuf [8]i2cCommand
}
func (*I2C) Configure
func (i2c *I2C) Configure(config I2CConfig) error
func (*I2C) ReadRegister
func (i2c *I2C) ReadRegister(address uint8, register uint8, data []byte) error
ReadRegister transmits the register, restarts the connection as a read operation, and reads the response.
Many I2C-compatible devices are organized in terms of registers. This method is a shortcut to easily read such registers. Also, it only works for devices with 7-bit addresses, which is the vast majority.
func (*I2C) SetBaudRate
func (i2c *I2C) SetBaudRate(br uint32) error
func (*I2C) Tx
func (i2c *I2C) Tx(addr uint16, w, r []byte) (err error)
Tx does a single I2C transaction at the specified address. It clocks out the given address, writes the bytes in w, reads back len(r) bytes and stores them in r, and generates a stop condition on the bus.
func (*I2C) WriteRegister
func (i2c *I2C) WriteRegister(address uint8, register uint8, data []byte) error
WriteRegister transmits first the register and then the data to the peripheral device.
Many I2C-compatible devices are organized in terms of registers. This method is a shortcut to easily write to such registers. Also, it only works for devices with 7-bit addresses, which is the vast majority.
type I2CConfig
type I2CConfig struct {
Frequency uint32 // in Hz
SCL Pin
SDA Pin
}
I2CConfig is used to store config info for I2C.
type I2CMode
type I2CMode int
I2CMode determines if an I2C peripheral is in Controller or Target mode.
type I2CTargetEvent
type I2CTargetEvent uint8
I2CTargetEvent reflects events on the I2C bus
type LEDCPWM
type LEDCPWM struct {
SigOutBase uint32 // GPIO matrix signal index for channel 0 (e.g. 73 on S3, 45 on C3)
NumChannels uint8
timerNum uint8 // 0–3: which LEDC timer (frequency) this PWM uses
dutyRes uint8
configured bool
channelPin [8]Pin
}
func (*LEDCPWM) Channel
func (pwm *LEDCPWM) Channel(pin Pin) (uint8, error)
func (*LEDCPWM) Configure
func (pwm *LEDCPWM) Configure(config PWMConfig) error
func (*LEDCPWM) Set
func (pwm *LEDCPWM) Set(channel uint8, value uint32)
func (*LEDCPWM) SetInverting
func (pwm *LEDCPWM) SetInverting(channel uint8, inverting bool)
func (*LEDCPWM) Top
func (pwm *LEDCPWM) Top() uint32
type NullSerial
type NullSerial struct {
}
NullSerial is a serial version of /dev/null (or null router): it drops everything that is written to it.
func (NullSerial) Buffered
func (ns NullSerial) Buffered() int
Buffered returns how many bytes are buffered in the UART. It always returns 0 as there are no bytes to read.
func (NullSerial) Configure
func (ns NullSerial) Configure(config UARTConfig) error
Configure does nothing: the null serial has no configuration.
func (NullSerial) ReadByte
func (ns NullSerial) ReadByte() (byte, error)
ReadByte always returns an error because there aren’t any bytes to read.
func (NullSerial) Write
func (ns NullSerial) Write(p []byte) (n int, err error)
Write is a no-op: none of the data is being written and it will not return an error.
func (NullSerial) WriteByte
func (ns NullSerial) WriteByte(b byte) error
WriteByte is a no-op: the null serial doesn’t write bytes.
type PDMConfig
type PDMConfig struct {
Stereo bool
DIN Pin
CLK Pin
}
type PWMConfig
type PWMConfig struct {
// PWM period in nanosecond. Leaving this zero will pick a reasonable period
// value for use with LEDs.
// If you want to configure a frequency instead of a period, you can use the
// following formula to calculate a period from a frequency:
//
// period = 1e9 / frequency
//
Period uint64
}
PWMConfig allows setting some configuration while configuring a PWM peripheral. A zero PWMConfig is ready to use for simple applications such as dimming LEDs.
type Pin
type Pin uint8
Pin is a single pin on a chip, which may be connected to other hardware devices. It can either be used directly as GPIO pin or it can be used in other peripherals like ADC, I2C, etc.
func (Pin) Configure
func (p Pin) Configure(config PinConfig)
Configure this pin with the given configuration.
func (Pin) Get
func (p Pin) Get() bool
Get returns the current value of a GPIO pin when the pin is configured as an input or as an output.
func (Pin) High
func (p Pin) High()
High sets this GPIO pin to high, assuming it has been configured as an output pin. It is hardware dependent (and often undefined) what happens if you set a pin to high that is not configured as an output pin.
func (Pin) Low
func (p Pin) Low()
Low sets this GPIO pin to low, assuming it has been configured as an output pin. It is hardware dependent (and often undefined) what happens if you set a pin to low that is not configured as an output pin.
func (Pin) PortMaskClear
func (p Pin) PortMaskClear() (*uint32, uint32)
Return the register and mask to disable a given GPIO pin. This can be used to implement bit-banged drivers.
Warning: only use this on an output pin!
func (Pin) PortMaskSet
func (p Pin) PortMaskSet() (*uint32, uint32)
Return the register and mask to enable a given GPIO pin. This can be used to implement bit-banged drivers.
Warning: only use this on an output pin!
func (Pin) Set
func (p Pin) Set(value bool)
Set the pin to high or low. Warning: only use this on an output pin!
func (Pin) SetInterrupt
func (p Pin) SetInterrupt(change PinChange, callback func(Pin)) (err error)
SetInterrupt sets an interrupt to be executed when a particular pin changes state. The pin should already be configured as an input, including a pull up or down if no external pull is provided.
You can pass a nil func to unset the pin change interrupt. If you do so, the change parameter is ignored and can be set to any value (such as 0). If the pin is already configured with a callback, you must first unset this pins interrupt before you can set a new callback.
type PinChange
type PinChange uint8
type PinConfig
type PinConfig struct {
Mode PinMode
}
type PinMode
type PinMode uint8
PinMode sets the direction and pull mode of the pin. For example, PinOutput sets the pin as an output and PinInputPullup sets the pin as an input with a pull-up.
type RingBuffer
type RingBuffer struct {
rxbuffer [bufferSize]volatile.Register8
head volatile.Register8
tail volatile.Register8
}
RingBuffer is ring buffer implementation inspired by post at https://www.embeddedrelated.com/showthread/comp.arch.embedded/77084-1.php
func (*RingBuffer) Clear
func (rb *RingBuffer) Clear()
Clear resets the head and tail pointer to zero.
func (*RingBuffer) Get
func (rb *RingBuffer) Get() (byte, bool)
Get returns a byte from the buffer. If the buffer is empty, the method will return a false as the second value.
func (*RingBuffer) Put
func (rb *RingBuffer) Put(val byte) bool
Put stores a byte in the buffer. If the buffer is already full, the method will return false.
func (*RingBuffer) Used
func (rb *RingBuffer) Used() uint8
Used returns how many bytes in buffer have been used.
type SPI
type SPI struct {
Bus interface{}
busID uint8
}
func (*SPI) Configure
func (spi *SPI) Configure(config SPIConfig) error
Configure and make the SPI peripheral ready to use. Implementation following ESP-IDF HAL with GPIO Matrix routing
func (*SPI) Transfer
func (spi *SPI) Transfer(w byte) (byte, error)
Transfer writes/reads a single byte using the SPI interface. Implementation following ESP-IDF HAL spi_ll_user_start with proper USER register setup
func (*SPI) Tx
func (spi *SPI) Tx(w, r []byte) error
Tx handles read/write operation for SPI interface. Since SPI is a synchronous write/read interface, there must always be the same number of bytes written as bytes read. This is accomplished by sending zero bits if r is bigger than w or discarding the incoming data if w is bigger than r. Optimized implementation ported from ESP32-C3 for better performance.
type SPIConfig
type SPIConfig struct {
Frequency uint32
SCK Pin // Serial Clock
SDO Pin // Serial Data Out (MOSI)
SDI Pin // Serial Data In (MISO)
CS Pin // Chip Select (optional)
LSBFirst bool // MSB is default
Mode uint8 // Mode0 is default
}
SPIConfig is used to store config info for SPI.
type Serialer
type Serialer interface {
WriteByte(c byte) error
Write(data []byte) (n int, err error)
Configure(config UARTConfig) error
Buffered() int
ReadByte() (byte, error)
DTR() bool
RTS() bool
}
type UART
type UART struct {
Bus *esp.UART_Type
Buffer *RingBuffer
}
func (*UART) Buffered
func (uart *UART) Buffered() int
Buffered returns the number of bytes currently stored in the RX buffer.
func (*UART) Configure
func (uart *UART) Configure(config UARTConfig)
func (*UART) Read
func (uart *UART) Read(data []byte) (n int, err error)
Read from the RX buffer.
func (*UART) ReadByte
func (uart *UART) ReadByte() (byte, error)
ReadByte reads a single byte from the RX buffer. If there is no data in the buffer, returns an error.
func (*UART) Receive
func (uart *UART) Receive(data byte)
Receive handles adding data to the UART’s data buffer. Usually called by the IRQ handler for a machine.
func (*UART) Write
func (uart *UART) Write(data []byte) (n int, err error)
Write data over the UART’s Tx. This function blocks until the data is finished being sent.
func (*UART) WriteByte
func (uart *UART) WriteByte(c byte) error
WriteByte writes a byte of data over the UART’s Tx. This function blocks until the data is finished being sent.
type UARTConfig
type UARTConfig struct {
BaudRate uint32
TX Pin
RX Pin
RTS Pin
CTS Pin
}
UARTConfig is a struct with which a UART (or similar object) can be configured. The baud rate is usually respected, but TX and RX may be ignored depending on the chip and the type of object.
type UARTParity
type UARTParity uint8
UARTParity is the parity setting to be used for UART communication.
type USBDevice
type USBDevice struct {
initcomplete bool
InitEndpointComplete bool
}
USBDevice provides a stub USB device for the ESP32-S3. The hardware only supports a fixed-function CDC-ACM serial port, so the programmable USB device features are no-ops.
func (*USBDevice) ClearStallEPIn
func (dev *USBDevice) ClearStallEPIn(ep uint32)
func (*USBDevice) ClearStallEPOut
func (dev *USBDevice) ClearStallEPOut(ep uint32)
func (*USBDevice) SetStallEPIn
func (dev *USBDevice) SetStallEPIn(ep uint32)
func (*USBDevice) SetStallEPOut
func (dev *USBDevice) SetStallEPOut(ep uint32)
type USB_DEVICE
type USB_DEVICE struct {
Bus *esp.USB_DEVICE_Type
Buffer *RingBuffer
txPending bool // unflushed data in the EP1 TX FIFO
txStalled bool // set when flushAndWait fails (no host reading); cleared when FIFO becomes writable
}
func (*USB_DEVICE) Buffered
func (usbdev *USB_DEVICE) Buffered() int
Buffered returns the number of bytes waiting in the receive ring buffer. It drains any data sitting in the hardware FIFO and re-enables the peripheral-level USB interrupt (which the ISR disables to prevent a level-triggered interrupt storm).
func (*USB_DEVICE) Configure
func (usbdev *USB_DEVICE) Configure(config UARTConfig) error
Configure initialises the USB Serial/JTAG controller.
func (*USB_DEVICE) DTR
func (usbdev *USB_DEVICE) DTR() bool
func (*USB_DEVICE) RTS
func (usbdev *USB_DEVICE) RTS() bool
func (*USB_DEVICE) ReadByte
func (usbdev *USB_DEVICE) ReadByte() (byte, error)
ReadByte returns a byte from the receive ring buffer.
func (*USB_DEVICE) Write
func (usbdev *USB_DEVICE) Write(data []byte) (n int, err error)
func (*USB_DEVICE) WriteByte
func (usbdev *USB_DEVICE) WriteByte(c byte) error