[fpc-pascal] Serial unit for Linux and Windows

[Marco van de Voort]

> I am planning to improve, if possible, the serial units for both Linux 
> and Windows, but have a few questions before I proceed any further:
> 
> 1- I guess the unit rtl\win\wininc\struct.inc has 2 bugs:
> 	a- bm_DCB_fRtsControl = $3000. It should be $2000.
> 	b- bm_DCB_fDtrControl = $30. It should be $20.
>     Can anybody confirm this?

No, they are correct. If you look into the headers you'll see:

 DWORD DCBlength;      /* sizeof(DCB)                     */
    DWORD BaudRate;       /* Baudrate at which running       */
    DWORD fBinary: 1;     /* Binary Mode (skip EOF check)    */
    DWORD fParity: 1;     /* Enable parity checking          */
    DWORD fOutxCtsFlow:1; /* CTS handshaking on output       */
    DWORD fOutxDsrFlow:1; /* DSR handshaking on output       */
    DWORD fDtrControl:2;  /* DTR Flow control                */
    DWORD fDsrSensitivity:1; /* DSR Sensitivity              */
    DWORD fTXContinueOnXoff: 1; /* Continue TX when Xoff sent */
    DWORD fOutX: 1;       /* Enable output X-ON/X-OFF        */
    DWORD fInX: 1;        /* Enable input X-ON/X-OFF         */
    DWORD fErrorChar: 1;  /* Enable Err Replacement          */
    DWORD fNull: 1;       /* Enable Null stripping           */
    DWORD fRtsControl:2;  /* Rts Flow control                */ 
    DWORD fAbortOnError:1; /* Abort all reads and writes on Error */
    DWORD fDummy2:17;     /* Reserved                        */
    WORD wReserved;       /* Not currently used              */
    WORD XonLim;          /* Transmit X-ON threshold         */
    WORD XoffLim;         /* Transmit X-OFF threshold        */
    BYTE ByteSize;        /* Number of bits/byte, 4-8        */
    BYTE Parity;          /* 0-4=None,Odd,Even,Mark,Space    */
    BYTE StopBits;        /* 0,1,2 = 1, 1.5, 2               */
    char XonChar;         /* Tx and Rx X-ON character        */
    char XoffChar;        /* Tx and Rx X-OFF character       */
    char ErrorChar;       /* Error replacement char          */
    char EofChar;         /* End of Input character          */
    char EvtChar;         /* Received Event character        */
    WORD wReserved1;      /* Fill for now.                   */
} DCB, *LPDCB;

Note the :2 with frts and fdtr. These are two bit values, not one bit, so a
mask that masks 2 bits makes sense
 
> 2- I will define TSerialFlags = set of (XOnXOffFlowControl, 
> RtsCtsFlowControl);
> What flags do we have to set in Linux to have XOnXOff handshaking? The 
> number of parameters in tios is mind boggling.

Well the existance of flags are named  "IXON", "IXOFF" and "IXANY" might
provide a clue when googled.

> 3- The Linux SerOpen function (based on fpopen) claims to return 0 if 
> the device could not be found. Shouldn't it be -1?

Probably. In 1.0.x times FPC unix functions had own error conventions.
 
> 4- Windows SerOpen function (based on CreateFile) returns an 
> INVALID_HANDLE_VALUE if the device could not be found. How to unify for 
> both Linux & Windows? Is it safe to return instead -1 (as in the Linux 
> case)?

See Tomas, it is define
> 
> 5- Is it OK to designate serial ports by COMx fow Windows and /dev/ttySx 
> for Linux?

No, since e.g a serial port on some other device might have a different
state. And strictly, this is even possible for Windows. Always keep naming
configurable and overridable. Those series are extremely common, but not
that 

Also note that serial.pp is a general unix unit, not just linux. So it needs
to work on FreeBSD too. (and maybe Mac, but I have no serial on my mac
anymore)

I've acquired a serial device suitable for testing with FreeBSD if needed.

> 6- Is it OK for TSerialState to include DCB for Windows and tios for Linux?

I don't understand what you mean with this.