58 Serial Manager

This chapter provides reference material for the serial manager API:

• Serial Manager Data Structures
  
  
• Serial Manager Functions
  

The header file SerialMgrOld.h declares the serial manager API. For more information on the serial manager, see the chapter "Serial Communication" in the Palm OS Programmer's Companion.

Serial Manager Data Structures

SerCtlEnum

To perform a control function, applications call SerControl, which performs one of the control operations specified by SerCtlEnum, which has the following elements:

Element	Description
serCtlFirstReserved = 0	Reserve 0
serCtlStartBreak	Turn RS232 break signal on. Applications have to make sure that the break is set long enough to generate a value BREAK! valueP = 0; valueLenP = 0
serCtlStopBreak	Turn RS232 break signal off: valueP = 0; valueLenP = 0
serCtlBreakStatus	Get RS232 break signal status (on or off): valueP = ptr to Word for returning status (0 = off, !0 = on) *valueLenP = sizeof(Word)
serCtlStartLocalLoopback	Start local loopback test; valueP = 0, valueLenP = 0
serCtlStopLocalLoopback	Stop local loopback test valueP = 0, valueLenP = 0
serCtlMaxBaud	valueP = ptr to DWord for returned baud *valueLenP = sizeof(DWord)
serCtlHandshakeThreshold	Retrieve HW handshake threshold; this is the maximum baud rate that does not require hardware handshaking valueP = ptr to DWord for returned baud *valueLenP = sizeof(DWord)
serCtlEmuSetBlockingHook	Set a blocking hook routine. WARNING! WARNING: For use with the Simulator on Mac OS only: NOT SUPPORTED ON THE PALM DEVICE. valueP = ptr to SerCallbackEntryType *valueLenP=sizeof(SerCallbackEntryType) Returns the old settings in the first argument.
serCtlLAST	Add new address entries before this one.

SerSettingsType

The SerSettingsType structure defines serial port attributes; it is used by the calls SerGetSettings and SerSetSettings. The SerSettingsPtr type points to a SerSettingsType structure.

typedef struct SerSettingsType {

    UInt32 baudRate;
    UInt32 flags;
    Int32 ctsTimeout;
    } SerSettingsType;

typedef SerSettingsType* SerSettingsPtr;

Field Descriptions

Serial Manager Functions

SerClearErr

Purpose

Reset the serial port's line error status.

Prototype

Err SerClearErr (UInt16 refNum)

Parameters

-> refNum

The serial library reference number.

Result

0

No error.

Comments

Call SerClearErr only after a serial manager function (SerReceive, SerReceiveCheck, SerSend, etc.) returns with the error code serErrLineErr.

The reason for this is that SerClearErr resets the serial port. So, if SerClearErr is called unconditionally while a byte is coming into the serial port, that byte is guaranteed to become corrupted.

The right strategy is to always check the error code returned by a serial manager function. If it `s serErrLineErr, call SerClearErr immediately. However, don't make unsolicited calls to SerClearErr.

When you get serErrLineErr, consider flushing the receive queue for a fraction of a second by calling SerReceiveFlush. SerReceiveFlush calls SerClearErr for you.

SerClose

Purpose

Release the serial port previously acquired by SerOpen.

Prototype

Err SerClose (UInt16 refNum)

Parameters

-> refNum

Serial library reference number.

Result

0

No error.

serErrNotOpen

Port wasn't open.

serErrStillOpen

Port still held open by another process.

Comments

Releases the serial port and shuts down serial port hardware if the open count has reached 0. Open serial ports consume more energy from the device's batteries; it's therefore essential to keep a port open only as long as necessary.

Caveat

Don't call SerClose unless the return value from SerOpen was 0 (zero) or serErrAlreadyOpen.

See Also

SerOpen

SerControl

Purpose

Perform a control function.

Prototype

Err SerControl (UInt16 refNum, UInt16 op, void *valueP, UInt16 *valueLenP)

Parameters

-> refNum

Reference number of library.

-> op

Control operation to perform (SerCtlEnum).

<-> valueP

Pointer to value for operation.

<-> valueLenP

Pointer to size of value.

Result

0

No error.

serErrBadParam

Invalid parameter (unknown).

serErrNotOpen

Library not open.

Comments

This function provides extensible control features for the serial manager. You can

• Turn on/off the RS232 break signal and check its status.
  
  
• Perform a local loopback test.
  
  
• Get the maximum supported baud rate.
  
  
• Get the hardware handshake threshold baud rate.
  

There is one emulator-only control, serCtlEmuSetBlockingHook. See Using the Serial Manager for more information.

Compatibility

Implemented only if 2.0 New Feature Set is present.

SerGetSettings

Purpose

Fill in the SerSettingsType structure with current serial port attributes.

Prototype

Err SerGetSettings (UInt16 refNum, SerSettingsPtr settingsP)

Parameters

-> refNum

Serial library reference number.

<-> settingsP

Pointer to SerSettingsType structure to be filled in.

Result

0

No error.

serErrNotOpen

The port wasn't open.

Comments

The information returned by this call includes the current baud rate, CTS timeout, handshaking options, and data format options.

See the SerSettingsType structure for more details.

See Also

SerSend

SerGetStatus

Purpose

Return the pending line error status for errors that have been detected since the last time SerClearErr was called.

Prototype

UInt16 SerGetStatus (UInt16 refNum, Boolean *ctsOnP, Boolean *dsrOnP)

Parameters

-> refNum

Serial library reference number.

-> ctsOnP

Pointer to location for storing a Boolean value.

-> dsrOnP

Pointer to location for storing a Boolean value.

Result

Returns any combination of the following constants, bitwise ORed together:

serLineErrorParity

Parity error.

serLineErrorHWOverrun

Hardware overrun.

serLineErrorFraming

Framing error.

serLineErrorBreak

Break signal detected.

serLineErrorHShake

Line handshake error.

serLineErrorSWOverrun

Software overrun.

Comments

When another serial manager function returns an error code of serErrLineErr, SerGetStatus can be used to find out the specific nature of the line error(s).

The values returned via ctsOnP and dsrOnP are not meaningful in the present version of the software

See Also

SerClearErr

SerOpen

Purpose

Acquire and open a serial port with given baud rate and default settings.

Prototype

Err SerOpen (UInt16 refNum, UInt16 port, UInt32 baud)

Parameters

-> refNum

Serial library reference number.

-> port

Port number.

-> baud

Baud rate.

Result

0

No error.

serErrAlreadyOpen

Port was open. Enables port sharing by "friendly" clients (not recommended).

serErrBadParam

Invalid parameter.

memErrNotEnoughSpace

Insufficient memory.

Comments

Acquires the serial port, powers it up, and prepares it for operation. To obtain the serial library reference number, call SysLibFind with "Serial Library" as the library name. This reference number must be passed as a parameter to all serial manager functions. The device currently contains only one serial port with port number 0 (zero).

The baud rate is an integral baud value (for example - 300, 1200, 2400, 9600, 19200, 38400, 57600, etc.). The Palm OS^® device has been tested at the standard baud rates in the range of 300 - 57600 baud. Baud rates through 1 Mbit are theoretically possible. Use CTS handshaking at baud rates above 19200 (see SerSetSettings).

An error code of 0 (zero) or serErrAlreadyOpen indicates that the port was successfully opened. If the port is already open when SerOpen is called, the port's open count is incremented and an error code of serErrAlreadyOpen is returned. This ability to open the serial port multiple times allows cooperating tasks to share the serial port. Other tasks must refrain from using the port if serErrAlreadyOpen is returned and close it by calling SerClose.

SerReceive

Purpose

Receives size bytes worth of data or returns with error if a line error or timeout is encountered.

Prototype

UInt32 SerReceive (UInt16 refNum, void *bufP, UInt32 count, Int32 timeout, Err* errP)

Parameters

refNum

Serial library reference number.

<-> bufP

Buffer for receiving data.

-> count

Number of bytes to receive.

-> timeout

Interbyte timeout in ticks, 0 for none, -1 forever.

<-> errP

For returning error code.

Result

Number of bytes received:

*errP = 0

No error.

serErrLineErr

RS232 line error.

serErrTimeOut

Interbyte timeout.

Compatibility

Implemented only if 2.0 New Feature Set is present.

---

NOTE:  

The old versions of SerSend and SerReceive are still available as SerSend10 and SerReceive10 (not V10).

---

See Also

SerReceive10

SerReceive10

Purpose

Receive a stream of bytes.

Prototype

Err SerReceive10 (UInt16 refNum, void *bufP, UInt32 bytes, Int32 timeout)

Parameters

-> refNum

The serial library reference number.

-> bufP

Pointer to the buffer for receiving data.

-> bytes

Number of bytes desired.

-> timeout

Interbyte time out in system ticks (-1 = forever).

Result

0

No error. Requested number of bytes was received.

serErrTimeOut

Interbyte time out exceeded while waiting for the next byte to arrive.

serErrLineErr

Line error occurred (see SerClearErr and SerGetStatus).

Comments

SerReceive blocks until all the requested data has been received or an error occurs. Because this call returns immediately without any data if line errors are pending, it is important to acknowledge the detection of line errors by calling SerClearErr. If you just need to retrieve all or some of the bytes which are already in the receive queue, call SerReceiveCheck first to get the count of bytes presently in the receive queue.

Compatibility

This function corresponds to the 1.0 version of SerReceive.

SerReceiveCheck

Purpose

Return the count of bytes presently in the receive queue.

Prototype

Err SerReceiveCheck (UInt16 refNum, UInt32 *numBytesP)

Parameters

-> refNum

Serial library reference number.

<-> numBytesP

Pointer to location for returning the byte count.

Result

0

No error.

serErrLineErr

Line error pending (see SerClearErr and SerGetStatus).

Comments

Because this call does not return the byte count if line errors are pending, it is important to acknowledge the detection of line errors by calling SerClearErr.

See Also

SerReceiveWait

SerReceiveFlush

Purpose

Discard all data presently in the receive queue and flush bytes coming into the serial port. Clear the saved error status.

Prototype

void SerReceiveFlush (UInt16 refNum, Int32 timeout)

Parameters

-> refNum

Serial library reference number.

-> timeout

Interbyte time out in system ticks (-1 = forever).

Result

Returns nothing.

Comments

SerReceiveFlush blocks until a timeout occurs while waiting for the next byte to arrive.

SerReceiveWait

Purpose

Wait for at least bytes bytes of data to accumulate in the receive queue.

Prototype

Err SerReceiveWait (UInt16 refNum, UInt32 bytes, Int32 timeout)

Parameters

-> refNum

Serial library reference number.

-> bytes

Number of bytes desired.

-> timeout

Interbyte timeout in system ticks (-1 = forever).

Result

0

No error.

serErrTimeOut

Interbyte timeout exceeded while waiting for next byte to arrive.

serErrLineErr

Line error occurred (see SerClearErr and SerGetStatus).

Comments

This is the preferred method of waiting for serial input, since it blocks the current task and allows switching the processor into a more energy-efficient state.

SerReceiveWait blocks until the desired number of bytes accumulate in the receive queue or an error occurs. The desired number of bytes must be less than the current receive queue size. The default queue size is 512 bytes. Because this call returns immediately if line errors are pending, it is important to acknowledge the detection of line errors by calling SerClearErr.

See Also

SerReceiveCheck, SerSetReceiveBuffer

SerSend

Purpose

Send one or more bytes of data over the serial port.

Prototype

UInt32 SerSend (UInt16 refNum, void *bufP, UInt32 count, Err *errP

Parameters

-> refNum

Serial library reference number.

-> bufP

Pointer to data to send.

-> count

Number of bytes to send.

<-> errP

For returning error code.

Result

Returns the number of bytes transferred.

Stores in errP:

0

No error.

serErrTimeOut

Handshake timeout.

The old calls worked, but they did not return enough info when they failed. The new calls (available in Palm OS v2.0 and greater) add more parameters to solve this problem and make serial communications programming simpler.

Don't call the new functions when running on Palm OS 1.0.

Compatibility

Implemented only if 2.0 New Feature Set is present.

---

NOTE:  

The old versions of SerSend and SerReceive are still available as SerSend10 and SerReceive10 (not V10).

---

See Also

SerSend10, SerSendWait

SerSend10

Purpose

Send a stream of bytes to the serial port.

Prototype

Err SerSend10 (UInt16 refNum, void *bufP, UInt32 size)

Parameters

-> refNum

Serial library reference number.

-> bufP

Pointer to the data to send.

-> size

Size (in number of bytes) of the data to send.

Result

0

No error.

serErrTimeOut

Handshake timeout (such as waiting for CTS to become asserted).

Comments

In the present implementation, SerSend10 blocks until all data is transferred to the UART or a timeout error (if CTS handshaking is enabled) occurs. Future implementations may queue up the request and return immediately, performing transmission in the background. If your software needs to detect when all data has been transmitted, see SerSendWait.

This routine observes the current CTS time out setting if CTS handshaking is enabled (see SerGetSettings and SerSend).

Compatibility

This function corresponds to the 1.0 version of SerSend.

See Also

SerSend, SerSendWait

SerSendFlush

Purpose

Discard all data presently in the transmit queue.

Prototype

Err SerSendFlush (UInt16 refNum)

Parameters

-> refNum

Serial library reference number.

Result

0

No error.

See Also

SerSend, SerSendWait

SerSendWait

Purpose

Wait until the serial transmit buffer empties.

Prototype

Err SerSendWait (UInt16 refNum, Int32 timeout)

Parameters

-> refNum

Serial library reference number.

-> timeout

Reserved for future enhancements. Set to (-1) for compatibility.

Result

0

No error.

serErrTimeOut

Handshake timeout (such as waiting for CTS to become asserted).

Comments

SerSendWait blocks until all data is transferred or a timeout error (if CTS handshaking is enabled) occurs. This routine observes the current CTS timeout setting if CTS handshaking is enabled (see SerGetSettings and SerSend).

See Also

SerSend

SerSetReceiveBuffer

Purpose

Replace the default receive queue. To restore the original buffer, pass bufSize = 0.

Prototype

Err SerSetReceiveBuffer (UInt16 refNum, void *bufP, UInt16 bufSize)

Parameters

-> refNum

Serial library reference number.

-> bufP

Pointer to buffer to be used as the new receive queue.

-> bufSize

Size of buffer, or 0 to restore the default receive queue.

Result

Returns 0 if successful.

Comments

The specified buffer needs to contain 32 extra bytes for serial manager overhead (its size should be your application's requirement plus 32 bytes). The default receive queue must be restored before the serial port is closed. To restore the default receive queue, call SerSetReceiveBuffer passing 0 (zero) for the buffer size. The serial manager does not free the custom receive queue.

SerSetSettings

Purpose

Set the serial port settings; that is, change its attributes.

Prototype

Err SerSetSettings (UInt16 refNum, SerSettingsPtr settingsP)

Parameters

-> refNum

Serial library reference number.

<-> settingsP

Pointer to the filled in SerSettingsType structure.

Result

0

No error.

serErrNotOpen

The port wasn't open.

serErrBadParam

Invalid parameter.

Comments

The attributes set by this call include the current baud rate, CTS timeout, handshaking options, and data format options. See the definition of the SerSettingsType structure for more details.

To do 7E1 transmission, OR together:

serSettingsFlagBitsPerChar7 | serSettingsFlagParityOnM | serSettingsFlagParityEvenM | serSettingsFlagStopBits1

If you're trying to communicate at speeds greater than 19.2 Kbps, you need to use hardware handshaking: serSettingsFlagRTSAutoM | serSettingsFlagCTSAutoM.

See Also

SerGetSettings