Technique for Obtaining Traces

We have a number of Tektronix TLA720 logic analyzers gathering data from the pins of Intel Pentium, Pentium II, and Xeon processors. The software we want to trace runs on the processor, under any of several different operating systems. When the buffer on the data analyzer is full, it sends a signal over to the Pentium's parallel port, triggering an interrupt. A special driver written for it sends it into a tight loop until the data analyzer is ready for more data. Meanwhile, the data analyzer sends the contents of its buffer over the network to a workstation that saves it into our tape array drive. A program on the workstation then goes through the raw data, saving out only the desired bits in a specific format, and then compresses it back to disk. This program then signals the data analyzer that it is ready for more data, causing the data analyzer to unlock the processor.

Currently, we are taking address traces from the chip, meaning that we record memory requests that the chip generates. This is useful for research involving caches. Each recorded request is made up of six bytes, in the following format:

4 address bytes, always ending in bits 000.
1 byte containing the byte enable pins, to determine which bytes were requested.
1 byte containing control information as follows:
bit 7 m/io (1 = memory access, 0 = IO access)
bit 6 d/c (1 = data access, 0 = instruction fetch)
bit 5 w/r (1 = write, 0 = read)
bit 4 (1 =, 0 =)
bit 3 (1 =, 0 =)
bit 2 (1 =, 0 =)
bit 1 (1 =, 0 =)
bit 0 (1 =, 0 =)

We are collecting traces from various operating systems, including Windows NT, Linux, and Windows 95. Device drivers which halt the machines as described above are available:

• Linux, available for kernel 2.2.x.
• Windows NT. not currently available online.
• Windows 95, not currently available online.