PDA

View Full Version : UART for development?



FranTaylor
11-08-2012, 05:11 PM
Is it possible to develop for the Teensy using the UART interface instead of the USB port?

If this can be done, then a 3-volt wired Teensy can be plugged straightaway into the UART pins of a Raspberry Pi, and the whole arrangement can be neatly tucked into a Raspberry Pi enclosure with no messy USB cables.

JBeale
11-08-2012, 05:48 PM
I think in order to do that, you would need to have a bootloader resident on the main ARM M4 chip, instead of on the smaller M0 device which the Teensy 3 currently uses. If true, I assume that could be a rather significant programming task. If this is just to make the wiring more tidy, you could probably use short wires soldered directly to one of the R-Pi USB connector pins (obviously, at the cost of 1 USB port). The Teensy 3 uses a 12 Mbps USB data rate which is a lot more forgiving of slightly messy wiring, than "Hi-Speed" USB at 480 Mbps.

FranTaylor
11-09-2012, 07:34 AM
I think in order to do that, you would need to have a bootloader resident on the main ARM M4 chip, instead of on the smaller M0 device which the Teensy 3 currently uses. If true, I assume that could be a rather significant programming task. If this is just to make the wiring more tidy, you could probably use short wires soldered directly to one of the R-Pi USB connector pins (obviously, at the cost of 1 USB port). The Teensy 3 uses a 12 Mbps USB data rate which is a lot more forgiving of slightly messy wiring, than "Hi-Speed" USB at 480 Mbps.

Thanks, thats what I was afraid of. What about the ICSP port? (There is one in there somewhere, yes?) Is this only good for burning the bootloader or can you load other code with it too?

JBeale
11-09-2012, 03:32 PM
On ARM chips, what you need for in-circuit programming are the JTAG pins. Right now they are only connected to the secondary small ARM-M0 chip which holds the bootloader. As far as I know, to do this you would have to unsolder those pins on the main ARM-M4, lift them up, attach wires and connect them to a JTAG programmer. At that point you might as well just buy a bare CPU chip, rather than the Teensy 3.

FranTaylor
11-09-2012, 04:05 PM
On ARM chips, what you need for in-circuit programming are the JTAG pins. Right now they are only connected to the secondary small ARM-M0 chip which holds the bootloader. As far as I know, to do this you would have to unsolder those pins on the main ARM-M4, lift them up, attach wires and connect them to a JTAG programmer. At that point you might as well just buy a bare CPU chip, rather than the Teensy 3.

Well, you can't solve every problem with one design. But I just have to say that I have investigated other alternative products and encountered a lot of unprofessionalism and shoddy workmanship, and so I am tempted to use the Teensy anyway just because it is plainly clear that pjrc is run by true professionals who understand how to make and sell a quality product.