Usb.h File Reference

usb-bridge communicates over USB via FTDI USB Bridge IC FT221X More...

#include <stdint.h>
#include <stdbool.h>
#include "ReadWriteBits.h"

Go to the source code of this file.

Typedefs
typedef uint8_t volatile *const	usb_reg
typedef uint8_t const	usb_pin

Enumerations
enum	ft_cmd { FtReadCmd =0xC6 , FtWriteCmd =0x86 }
enum	ft_databus_pin_direction { FtIn =0x00 , FtOut =0xFF }
enum	ft_status { FtError =0 , FtOk =1 }
enum	ft_clock_edge { FtSample =0 , FtDrive =1 }

Functions
void	_FtClockDatabus (uint8_t direction)
void	_FtReadDatabus (uint8_t *pbyte)
void	_FtWriteDatabus (uint8_t byte)
void	_FtDatabusPinDirection (uint8_t pin_direction)
void	FtSelectFT221X (void)
void	FtUnselectFT221X (void)
void	FtBusTurnaround (void)
bool	FtIsOk (void)
void	FtRead (uint8_t *pbyte)
void	FtWrite (uint8_t byte)
bool	UsbRxbufferIsEmpty (void)
bool	UsbTxbufferIsFull (void)
uint8_t	UsbReadByte (uint8_t *pbyte)
uint8_t	UsbWriteByte (uint8_t byte)

Variables
usb_reg	FtCtrl_port
usb_reg	FtCtrl_pin
usb_reg	FtData_pin
usb_reg	FtData_ddr
usb_reg	FtData_port
usb_pin	FtMiso
usb_pin	FtChipSelect
usb_pin	FtClock
usb_pin	FtMiosio0

Detailed Description

usb-bridge communicates over USB via FTDI USB Bridge IC FT221X

• USB host sees FT221X as a USB device
• Two options for host to communicate with this USB device:
  1. use generic USB serial device driver, e.g., pyserial
  2. use the D2XX driver to access the expanded functionality of the FTDI USB API
• The usb-bridge microcontroller sees FT221X as an FT1248 slave

Flow from USB host to usb-bridge microcontroller:

• USB host writes to FT221X
• now FT221X has data in its receive buffer:
  • pin FT1248 MISO asserts LOW
  • this signals to the usb-bridge microcontroller that data is available
• usb-bridge microcontroller reads the data

Flow from usb-bridge microcontroller to USB host:

• Control lines
  • FtClock
    • the clock idles LOW
    • the clock is only active during FT1248 communication
• Sending a single byte takes three clock cycles
• TODO: multi-byte communication where each additional byte only adds one clock cycle
• Databus pin direction
  • databus pins are FtMiosio0 through FtMiosio7
  • the databus is bi-directional
    • FtRead: the FT221X drives the databus
    • FtWrite the microcontroller drives the databus
  • databus pins are usually microcontroller inputs
  • microcontroller only outputs to the databus during an FtWrite
    • the microcontroller pins are outputs for the interval
    • starting after a clock rising edge
    • ending before the next clock rising edge
• TODO: fill this in

Definition in file Usb.h.

Function Documentation

_FtClockDatabus()

void _FtClockDatabus ( uint8_t  direction )

inline

FtClockDatabus behavior:

• drives FtClock HIGH if direction is FtDrive
  
• drives FtClock LOW if direction is FtSample
  

Definition at line 84 of file Usb.h.

_FtDatabusPinDirection()

void _FtDatabusPinDirection ( uint8_t  pin_direction )

inline

FtDatabusPinDirection behavior:

• makes databus pins outputs if direction is FtOut
  
• makes databus pins inputs if direction is FtIn
  

Definition at line 108 of file Usb.h.

_FtReadDatabus()

void _FtReadDatabus ( uint8_t *  pbyte )

inline

FtReadDatabus behavior:

• copies databus pin values to address pbyte
  

Definition at line 94 of file Usb.h.

_FtWriteDatabus()

void _FtWriteDatabus ( uint8_t  byte )

inline

FtWriteDatabus behavior:

• outputs byte on databus pins
  

Definition at line 101 of file Usb.h.

FtBusTurnaround()

void FtBusTurnaround ( void  )

inline

FtBusTurnaround behavior:

• clocks one cycle to signal data drive then data sample
  

Definition at line 136 of file Usb.h.

FtIsOk()

bool FtIsOk ( void  )

inline

The FT221X indicates data transfer status on Pin MISO while FT1248 communication is active.
LOW on pin MISO means FT221X status is OK.

• See the 8-bit write and 8-bit read timing diagrams:
  • FT221X datasheet
• See ACK/NAK details in section FT1248: NAK:
  • FTDI application note AN167

Timing diagram and ACK/NAK summary:

• During the BUS TURNAROUND after the COMMAND PHASE
  • if command is 8-bit read
    • LOW indicates receive buffer has data to read
    • HIGH indicates receive buffer is empty
  • if command is 8-bit write
    • LOW indicates transmit buffer has room to write
    • HIGH indicates transmit buffer is full
• During the DATA phase
  • after the clock rising edge
    • FT221X outputs an ACK or NAK on MISO
    • ACK:
      • MISO is LOW
      • indicates a successful data transfer
    • NAK:
      • MISO is HIGH
      • indicates a failed data transfer
  • after clock falling edge:
    • Microcontroller reads MISO
      • LOW indicates ACK
      • HIGH indicates NAK
• Data transers fail because of either:
  • a buffer full condition on writing data to the FT221X
  • a buffer empty condition on reading data from the FT221X

FtIsOk behavior:

• returns true if FtMiso is LOW
  
• returns false if FtMiso is HIGH
  

Definition at line 149 of file Usb.h.

FtRead()

void FtRead ( uint8_t *  pbyte )

inline

FtRead behavior:

• clocks one byte out of the FT221X
  
• stores the byte at address pbyte
  

Definition at line 197 of file Usb.h.

FtSelectFT221X()

void FtSelectFT221X ( void  )

inline

FtSelectFT221X behavior:

• drives FtChipSelect LOW
  

Definition at line 118 of file Usb.h.

FtUnselectFT221X()

void FtUnselectFT221X ( void  )

inline

FtUnselectFT221X behavior:

• drives FtChipSelect HIGH
  

Definition at line 125 of file Usb.h.

FtWrite()

void FtWrite ( uint8_t  byte )

inline

FtWrite behavior:

• signals to drive data onto the databus
  
• sets microcontroller databus pins as outputs
  
• outputs byte on databus pins
  
• signals FT221X to sample the databus
  
• sets microcontroller databus pins as inputs
  

Definition at line 209 of file Usb.h.

UsbReadByte()

uint8_t UsbReadByte ( uint8_t *  pbyte )

inline

UsbReadByte behavior:

• selects the FT221X
  
• drives databus with read command
  
• signals FT221X to sample the databus
  

Definition at line 262 of file Usb.h.

UsbRxbufferIsEmpty()

bool UsbRxbufferIsEmpty ( void  )

inline

UsbRxbufferIsEmpty behavior:

• returns true if pin FT1248 MISO is HIGH
  
• returns false if pin FT1248 MISO is LOW
  

Definition at line 237 of file Usb.h.

UsbTxbufferIsFull()

bool UsbTxbufferIsFull ( void  )

inline

UsbTxbufferIsFull behavior:

• returns true if pin MIOSIO0 is HIGH
  
• returns false if pin MIOSIO0 is LOW
  

Definition at line 245 of file Usb.h.