Motorola MC68328 Informações Técnicas descarregar pdf (Página 27)

Software Development

FLEX System Software

FLEX Alphanumeric Chip MC68175 Interface 3-9

In the second stage, the host software periodically calls the FLEX One-Way Stack

function to read data out of the circular queue. FLEX One-Way Stack then analyzes and

assembles the original FLEX page and returns it to the host software.

Two pointers (index variables) are used to manage the circular queue, gPackWrite and

gPackRead. The gPackWrite variable points to the next available byte in the queue for data

storage. The pointer gPackWrite advances for every byte of data that the FLEX

Alphanumeric Chip SPI interrupt handler receives. The gPackRead variable points to the

next byte of data in the queue to be read and processed. The pointer gPackRead advances

every time FLEX One-Way Stack reads a byte out of the queue for processing. Product

developers can manage the size of the circular queue. However, the size of the queue (in

bytes) must be a multiple of four to avoid splitting of packets (1 packet = 32 bits = 4

bytes). The circular queue is defined as shown in Example 3-1

Figure 3-5 Circular Queue for Data Storage

The host software can either poll the two pointers or use a timer interrupt to check them

for new data in the circular queue, shown in Figure 3-5. If the FLEX One-Way Stack

finishes assembling the original page (meaning that no other fragment of the page is

expected), FLEX One-Way Stack notifies the host software by calling the function

FStkNotifyNewMsg(). Product engineers can implement FStkNotifyNewMsg () in

accordance with the individual features of each product, such as alerting the user or

retrieving and displaying the message on the LCD.

Example 3-1 Circular Queue Definition

unsigned char gPacketQ[PAKQ_SIZE];

gPackRead

gPackWritegPackRead

Queue with No Data (Empty)

Queue after Interrupt Handler

Receives Data from FLEX

Queue after FLEX One-Way

Stack Processes Data

1230

gPackWrite

Alphanumeric Chip

AA1426

1230

gPackWritegPackRead

Frees

cale Semiconductor,

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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