Intel IXP400 manual Internal Bus PMU, Counter Buffer Overflow

Intel® IXP400 Software

Access-Layer Components: Performance Profiling (IxPerfProfAcc) API

Event-based sampling will allow the client to identify the “hot spots” of the program for further optimization. In this method, the sampling rate is the number of events before a counter overflow interrupt is generated. This sampling rate is defined by the client. As in time-based sampling, the PC value of each sample and frequency will be determined. This allows the client to identify the sections of code that cause each event.

Time-based sampling and event-based sampling, and event counting must not be performed concurrently. The client should be aware of the data memory required to perform each of these operations.

Event-based sampling allows the client to sample up to four events at a time. The maximum data memory required to store the results, in the event that the client chooses to perform event-based sampling with four events simultaneously, is about 4 Mbytes, and about 1 Mbytes for time-based sampling. In the event of an overflow in the results buffer, the client will be notified.

The PerfProf module provides the client with APIs to start and stop the collections of events. It will provide an API that reads and stores the value of all the counters. It will also enable the client to measure the latency (in clock cycles) between any two Intel XScale core instructions in a program.

Furthermore, the module will allow the client to determine the frequency with which Intel XScale core code is being executed.

17.3.1Counter Buffer Overflow

The PerfProf module will allow the client to count up to four different events simultaneously and will also handle the overflow of these counters. In the case of overflow, the module will need to register an interrupt service routine. However, the handling of overflow will have a minimal impact on the running system.

The program shall keep track of the number of times a buffer has over flowed. The necessary adjustments will then be made to the final count value, to ensure an accurate value.

17.4Internal Bus PMU

The internal bus PMU enables performance management of components accessing or utilizing the north and south bus. This includes statistics of the bus itself.

The counters monitor two types of events, which are occurrence events and duration events. The occurrence event causes the counter to increase by one, each time the event occurs. For duration events, the counter counts the number of clocks during which a particular condition or a set of conditions is true.

This PMU is able to monitor and gather statistics on SDRAM, north bus, south bus, north masters, north slaves, south masters, south slaves, and miscellaneous items like the cycle count. Among the details being monitored are:

•North bus usage — The north bus occupancy reported by the PMU.

This is done by taking a snapshot of the total cycle count and subtracting the idle time.

•South bus usage — The south bus occupancy reported by the PMU.

This is done by taking a snapshot of the total cycle count and subtracting the idle time.

Programmer’s Guide	IXP400 Software Version 2.0	April 2005
	Document Number: 252539, Revision: 007	249