But I was assured that the BSDL file would work just fine with the silicon revision of the chip I had. I've had the luck to get access to the BSDL file, under NDA, even though it wasn't for the exact silicon revision I was debugging.
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The reason for the secrecy being that they essentially give away a part of their hardware design, which most of these hardware vendors consider a trade secet. Otherwise they tend to be pretty secretive about it. The term boundary scan is still used to describe the process and makes up part of the acronym BSDL ( boundary scan description language), which you would normally get in touch with if you were to boundary scan a device/chip and the vendor expected you to do that. Keep in mind that this was established before the WWW came to be and that a lot of information regarding it has been banned onto dead trees. IDCODE is used to identify the device and a few basic characteristics.Ī neat overview of some technical details can be found here: JTAG - A technical overview, but the Wikipedia article and its reference list also provide valuable information. The instruction BYPASS is used to tell a device earlier on the chain to ignore your commands and pass them on. So you can test the various components through one port. On a PCB the chip(s) and peripherals form a "daisy chain" connected to the TAP (test access port). They used to be connected to the parallel port of your machine, but these days are more often connected via USB and based on one of the FTDI chips. The devices used to do the boundary scan according to JTAG are called JTAG probes.
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after development of the hardware and subsequent production of it. The idea was to define an interface that could be used to test hardware (micro controllers and connected peripherals after manufacturing). The process is called boundary scanning and JTAG was named after the working group: Joint Test Action Group, some time in the 1980s. JTAG was initially created to test/verify hardware devices.