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Noob question about TI Stellaris Launchpad EK-LM4F120XL

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I realized upon unboxing this board, it has two identical LX4F120H ARM mcus, so the left one's purpose is solely for ICDI function only ?

Just curious why need such powerful auxiliary chip for just the in circuit debug feature ? Again, this is a noob question here.  :P


First I will make the assumption that this processor (the target processor) is an ARM cortex m4 that  is using the standard ARM JTAG/SWD circuitry and not some proprietary interface (I haven't read the data sheet). It does not require anything like  another cortex m4 to run the JTAG, all you need is a USB to serial like FTDI 2232, Dangerous prototype's Bus Blaster for example. Although I am almost certain the FTDI chip also has a common core processor (could be an 8051 derivative - don't quote me) onboard. All of the semi manufactures use one of their own  chips to provide jtag for their development boards . NXP uses an LPC1343 in their  LPCExpresso series, ST uses a STM32F103 in their  ST-Link2 STM32 Discovery boards ect. Why wouldn't they use their own products?

Of course, when a company does a demo board they want to use their own chips on it for as much stuff as possible. It is a prestige thing to not have competitor products on a demo board.

Why they used the same chip? Maybe to reduce production cost. It is one feeder less for the pick and place machine. It makes logistics, procuring and storing the different parts for production a bit simpler.

The hardware team, when designing the board, only has to deal with one kind of MCU. One datasheet less to study. The same basic connection for things like power and clock. Same footprint. Same for the software team doing the firmware and demo software. It only has to deal with one kind of MCU.

We can also safely assume that TI's internal cost for the chip is fare less than it's official list price. In the end using the totally oversized MCU was maybe even cheaper than using something else.


--- Quote from: BravoV on November 10, 2012, 06:21:04 am ---Just curious why need such powerful auxiliary chip for just the in circuit debug feature ?

--- End quote ---

Reflected sound as of underground spirits.

JTAG and SWD are not very well suited to run over USB. By putting more smarts into the adapter, you can use better protocols over the (relatively) high latency bus, and translate into JTAG or SWD commands locally. Why TI chose an LX4F120H in particular is anyone's guess. Could have been a case of dogfooding on part of the Launchpad team, or making a point of the chips being so cheap you can put two of them on a single board or whatever.


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