How To Manage Queues; Switching Master And Slave Mode - NXP Semiconductors freescale KV4 Series Reference Manual

Table of Contents

44.6.1 How to manage queues

The queues are not part of the module, but it includes features in support of queue

management. Queues are primarily supported in SPI configuration.

1. When module executes last command word from a queue, the EOQ bit in the

command word is set to indicate it that this is the last entry in the queue.

2. At the end of the transfer, corresponding to the command word with EOQ set is

sampled, the EOQ flag (EOQF) in the SR is set.

3. The setting of the EOQF flag disables serial transmission and reception of data,

putting the module in the Stopped state. The TXRXS bit is cleared to indicate the

Stopped state.

4. The DMA can continue to fill TX FIFO until it is full or step 5 occurs.

5. Disable DMA transfers by disabling the DMA enable request for the DMA channel

assigned to TX FIFO (and CMD FIFO) and RX FIFO. This is done by clearing the

corresponding DMA enable request bits in the DMA Controller.

6. Ensure all received data in RX FIFO has been transferred to memory receive queue

by reading the RXCNT in SR or by checking RFDF in the SR after each read

operation of the POPR.

7. Modify DMA descriptor of TX and RX channels for new queues

8. Flush TX FIFO (and CMD FIFO) by writing a 1 to the CLR_TXF bit in the MCR.

Flush RX FIFO by writing a '1' to the CLR_RXF bit in the MCR.

9. Clear transfer count either by setting CTCNT bit in the command word of the first

entry in the new queue or via CPU writing directly to SPI_TCNT field in the TCR.

10. Enable DMA channel by enabling the DMA enable request for the DMA channel

assigned to the module TX FIFO, (and CMD FIFO) and RX FIFO by setting the

corresponding DMA set enable request bit.

11. Enable serial transmission and serial reception of data by clearing the EOQF bit.

When changing modes in the module, follow the steps below to guarantee proper

Freescale Semiconductor, Inc.

KV4x Reference Manual, Rev. 2, 02/2015

Chapter 44 Serial Peripheral Interface (SPI)