Texas Instruments TMS320C645x manual CPU Interrupts, General Description

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Interrupt Conditions

4Interrupt Conditions

This section defines the CPU interrupt capabilities and requirements of the peripheral.

4.1CPU Interrupts

The following interrupts are supported by the RIO peripheral.

∙Error Status: Event indicating that a run-time error was reached. The CPU should reset/resynchronize the peripheral.

∙Critical Error: Event indicating that a critical error state was reached. The CPU should reset the system.

∙CPU servicing: Event indicating that the CPU should service the peripheral.

4.2General Description

The RIO peripheral is capable of generating various types of CPU interrupts. The interrupts serve two general purposes: error indication and servicing requests.

Since RapidIO is a packet oriented interface, the peripheral must recognize and respond to inbound signals from the serial interface. There are no GPIO or external pins used to indicate an interrupt request. Thus, the interrupt requests are signaled either by an external RapidIO device through the packet protocols discussed as follows, or are generated internally by the RIO peripheral.

CPU servicing interrupts lag behind the corresponding data, which was generally transferred from an external processing element into local L2 memory. This transfer can use a messaging or direct I/O protocol. When the single or multi-packet data transfer is complete, the external PE, or the peripheral itself, must notify the local processor that the data is available for processing. To avoid erroneous data being processed by the local CPU, the data transfer must complete through the DMA before the CPU interrupt is serviced. This condition could occur since the data and interrupt queues are independent of each other, and DMA transfers can stall. To avoid this condition, all data transfers from the peripheral through the DMA use write-with-response DMA bus commands, allowing the peripheral to always be aware that outstanding transfers have completed. Interrupts are generated only after all DMA bus responses are received. Since all RapidIO packets are handled sequentially, and submitted on the same DMA priority queue, the peripheral must keep track of the number of DMA requests submitted and the number of responses received. Thus, a simple counter within the peripheral ensures that data packets have arrived in memory before submitting an interrupt.

The sending device initiates the interrupt by using the RapidIO defined DOORBELL message. The DOORBELL packet format is shown in Figure 42. The DOORBELL functionality is user-defined. This packet type is commonly used to initiate CPU interrupts. A DOORBELL packet is not associated with a particular data packet that was previously transferred, so the INFO field of the packet must be configured to reflect the DOORBELL bit to be serviced for the correct TID info to be processed.

Figure 42. RapidIO DOORBELL Packet for Interrupt Use

PHY	TRA	LOG	TRA	LOG
10	2	4	16	32

PHY

16

acklD	rsv	prio	tt	1010	destID	sourcelD	Reserved			srcTID	info			info		CRC
5	3	2	2	4	8	8		8		8	8		8		16
						9				2	1		4
						Reserved			Doorbell			rsv	Doorbell

74 Serial RapidIO (SRIO) SPRU976 –March 2006

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