A Virtex chip can be configured via its dedicated JTAG pins.
There is a software requirement for configuring a single Virtex device via JTAG. At a minimum, you must use A1.5i/F1.5i or better software when creating a Virtex design that will be loaded via JTAG.
(1) Create a .bit file which uses the following option in bitgen.
bitgen -g startupclk:jtagclk designName.ncd Where designName is the name of the routed ncd file.
If you do not do this the Virtex device will accept the bitstream, DONE will be high and /INIT will be high, but the device will not respond to stimulus. This option tells the Virtex device to use the JTAG clocks on the TCK pin to finish the configuration process.
If you do not wish to use the TCK to clock the startup sequence then you must use the STARTUP_VIRTEX symbol to attach a specific internal clock net to be used for the startup sequence. Bitgen must then be instructed to use the userclk for startup with the option -g:userclk
Failure to do either of these options will result in an incomplete device configuration.
(2) After creating a bitstream as per step 1, prepare the Virtex device for JTAG configuration. If you are using the JTAG Programmer software, then do not read any further. If you are using a JTAG tester or writing your own software, the following applys:
An individual Virtex device can be configured via JTAG in two different ways.
In the first method, an already configured Virtex device is re-configured via JTAG by toggling the TAP and entering the CFG_IN instruction. In the second method, an individual Virtex device is configured after power-up via JTAG exclusively.
If you are configuring a Virtex device via JTAG only, then it is reccomended to set the mode pins of the Virtex device to 101 (M2=1,M1=0,M0=1 NOPULLUPS) or 001 (M2=0,M1=0,M0=1 PULLUPS). If you do not set the mode pins to 101 or 001 before power-up, you risk accidental configuration in another mode.
(3) After physically preparing the individual Virtex device, and creating the bitstream with the correct bitgen options, follow these instructions to load the bitstream.
(a) On power-up, place a '1' on TMS and clock TCK five times. This takes the TAP through the Test-Logic-Reset (TLR) state.
(b) Move to the Shift-IR state.
(c) In the Shift-IR state, load the CFG_IN instruction.
(d) Go to the Shift-DR state and shift in the Virtex bitstream. When the entire bitstream has been shifted in, leave the Shift-DR state and go to the Test-Logic-Reset state.
(e) From the Test-Logic-Reset state, go to Shift-IR and load in the JSTART instruction. After loading the JSTART instruction, go to the Shift-DR state and apply at a minimum 10 clocks to TCK.
(g) After applying the clocks to TCK, return to Test-Logic-Reset.
The device will now be functional.
Troubleshooting the JTAG Configuration of an Individual Virtex Device
Note that the TAP is always active on Virtex devices and can be used for troubleshooting. In JTAG configuration mode, DONE functions exactly as it does in non-JTAG configuration mode. While in JTAG configuration mode with Virtex, the DONE pin can be monitored to see if the bitstream has been successfully loaded into the device. If DONE is low three things are possible: the entire bitstream hasn't been sent, the entire bitstream has been sent but the startup sequence has not finished, or an error has happened. If DONE goes high, this means that the Virtex device has received the entire bitstream and that the bitstream was not corrupted.
If DONE has not gone high , the bitstream has been created with the -g option for jtagclk, and the JSTART instruction has been executed, it is possible that an error in the bitstream was detected. In non-JTAG configuration of a Virtex device, this sort of failure is revealed via the /INIT pin. In Virtex JTAG configuration, the external /INIT pins not used for reporting status. It is possible to view the internal /INIT signal. After finishing a Virtex JTAG configuration where the DONE pin stays low, do the following to see if an error in the bitstream was detected:
(a) Move the TAP to the test-logic-reset state. (b) Load the CFG_IN instruction. (c) go to the Shift-DR state and shift in this 64-bit pattern:
2 8 0 0 E 0 0 1 0 0 0 0 0 0 0 0 0010 1000 0000 0000 1110 0000 0000 0001 0000 0000 0000 0000 0000 0000 0000 0000 ^ | Shift in data starting from this bit.
(d) Load the CFG_OUT instruction. (e) go to Shift-DR and clock TCK 32 times while reading TDO.
The data is the contents of the STATUS register. The last bit out will be a 1 if there was a CRC error. After a successful configuration the 32 bits would normally be:
The rightmost bit is the last one shifted out. If the returned values deviates from the above there may be a problem with your configuration. For a complete description of the bits in the STATUS register please see Xilinx Application Note (Xilinx XAPP151) "Virtex Configuration Architecture Advanced Users' Guide"