Am 06/10/2011 09:51 PM, schrieb Tomek CEDRO: > On Fri, Jun 10, 2011 at 7:17 PM, Michael Schwingen > <rincew...@discworld.dascon.de> wrote: >> If we agree that we do not want to touch the target, that means the >> lowlevel interface driver must not change any signal state upon exit, >> because it does not know what state that will put the target into. > If you disconnect the dongle then the target is definitely immune to > changes on that dongle. > >> Changing signals to High-Z is *not* safe. It changes the JTAG signals to >> a board-specific state that depends on the pullup/pulldown resistors on >> the board. Depending on the old state of the JTAG pins, this may cause a >> clock on TCK, with random values on the other pins. > Michael, please read carefully, I think you don't understand what we > say. There is more philosophy in your talk than it should be. The > pull-up or pull-down resistors are used in the electronics to protect > against random input states. If you switch output into Hi-Z the > pull-up or pull-down resistor will take care of the on the pin state. Exactly. And that state may well be different from the state OpenOCD drove the pin to. For example, in case of a pullup, if OpenOCD drives the pin to "L", and we disconnect, placing the pin in High-Z, the pin will see a "H" via the pullup - this is a L-H-transition that may cause unwanted operations on the target.
If OpenOCD drives the Pin to "L" and the board has a pulldown, then nothing happens. However, neither OpenOCD nor the FTDI driver can know if this is the case. cu Michael _______________________________________________ Openocd-development mailing list Openocd-development@lists.berlios.de https://lists.berlios.de/mailman/listinfo/openocd-development
