SCI: Data Link Layer

SCI Data Link Layer. More...

Collaboration diagram for SCI: Data Link Layer:

Macros
#define	SCI_ALLOW_NEWLINE   1
	Whether to allow newline ( ) in print / log messages.
#define	SCI_CMD_IS_EXTENDED_CMD(cmd)   ((cmd) & 0x80)
	Checks whether the command byte is an extended command (= MSB set).

Functions
status_t	SCI_DataLink_Init (void)
	Initialize the data link module.
status_t	SCI_DataLink_CheckRxFrame (sci_frame_t *frame)
	Checks the CRC checksum for a RX frame.
void	SCI_DataLink_ReleaseFrames (sci_frame_t *frame)
	Releases the frame queue.
void	SCI_DataLink_ResetRxFrames (sci_frame_t *frame)
	Resets the frame read pointer to the very first byte (= command byte).
bool	SCI_DataLink_IsTxBusy (void)
	Returns whether the TX line is currently busy and data is being sent.
status_t	SCI_DataLink_SendTxFrame (sci_frame_t *frame, bool high_priority)
	Trigger the data transfer and releases the TX buffers.
sci_frame_t *	SCI_DataLink_RequestTxFrame (bool queueStartByte)
	Find an unused TX buffer from the queue and prepare it with a start byte.

Detailed Description

SCI Data Link Layer.

---

Implements the data link layer protocol for systems communication interface that connects to an external device. It takes care of sending and receiving data frames and thus byte stuffing and CRC check.

Remarks:

• Transmitting frames:
  • Two buffers: one for preparing data, one for sending at the same time.
  • If UART TX Line is still busy when trying to send new data, the program is delayed until TX is idle.
• Receiving frames:
  • Special frame buffers collect data from RX (w/o escape bytes)
  • Only data between START and STOP is collected.
  • After STOP was received, the FrameReceivedCallback is invoked.

Macro Definition Documentation

SCI_ALLOW_NEWLINE

#define SCI_ALLOW_NEWLINE   1

Whether to allow newline (
) in print / log messages.

---

SCI_CMD_IS_EXTENDED_CMD

#define SCI_CMD_IS_EXTENDED_CMD

(

cmd

)

((cmd) & 0x80)

Checks whether the command byte is an extended command (= MSB set).

---

Function Documentation

SCI_DataLink_CheckRxFrame()

status_t SCI_DataLink_CheckRxFrame

(

sci_frame_t *

frame

)

Checks the CRC checksum for a RX frame.

---

Parameters

frame

The RX frame which requires CRC checking.

Returns

Returns the status:

• STATUS_OK (0) on success.
• ERROR_SCI_CRC_FAILED if the CRC failed.

SCI_DataLink_Init()

status_t SCI_DataLink_Init

(

void

)

Initialize the data link module.

---

Initialization implies the following steps:

• Initialization of the SCI Hardware Layer, i.e. UART/LPSCI.
• Starts to listen to incoming UART data and calls the frame received callback.
• Initialization of the CRC module.

Returns

Returns the status (STATUS_OK on success).

SCI_DataLink_IsTxBusy()

bool SCI_DataLink_IsTxBusy

(

void

)

Returns whether the TX line is currently busy and data is being sent.

---

Returns

Returns true if the TX line is busy sending data.

SCI_DataLink_ReleaseFrames()

void SCI_DataLink_ReleaseFrames

(

sci_frame_t *

frame

)

Releases the frame queue.

---

Parameters

frame

The frame queue to be released.

SCI_DataLink_RequestTxFrame()

sci_frame_t * SCI_DataLink_RequestTxFrame

(

bool

queueStartByte

)

Find an unused TX buffer from the queue and prepare it with a start byte.

---

If sending data over the SCI, an new and empty TX frame needs to be claimed for usage of the command. This functions finds one and prepares it with an start byte. A pointer to the frame is returned if one is found. Otherwise null, so checking for null pointer is recommended!

Parameters

queueStartByte

Whether to queue a start byte into the buffer.

Returns

Returns a pointer to an free TX frame, zero if no one is currently available.

SCI_DataLink_ResetRxFrames()

void SCI_DataLink_ResetRxFrames

(

sci_frame_t *

frame

)

Resets the frame read pointer to the very first byte (= command byte).

---

Parameters

frame

The frame queue to reset.

SCI_DataLink_SendTxFrame()

status_t SCI_DataLink_SendTxFrame	(	sci_frame_t *	frame,
		bool	high_priority
	)

Trigger the data transfer and releases the TX buffers.

---

Before the frame is transferred, a stop byte is added to the end of the data buffer.

Parameters

frame	The frame to be sent.
high_priority	If set, the frame is queued right after the current frame. If not set, the frame is queued at the very end of the frame queue.

Returns

Returns the status (STATUS_OK on success).