Altera Virtual JTAG IP Core - Manual (Page 17)

Each
device_virtual_ir_shift
command issues a
USER1
instruction to the JTAG Instruction Register
followed by a DR shift containing the VIR value provided by the
ir_value
argument prepended by address
bits to target the correct SLD node instance.
Use the
-no_captured_ir_value
argument if you do not care about shifting out the contents of the
current VIR value. Enabling this argument increases the speed of the VIR shift transaction by
eliminating a command cycle within the underlying transaction.
Note:
Similarly, each
device_virtual_dr_shift
command issues a
USER0
instruction to the JTAG Instruction
Register followed by a DR shift containing the VDR value provided by the dr_value argument. These
commands return the underlying JTAG transactions with the
show_equivalent_device_ir_dr_shift
option set.
The device_virtual_ir_shift takes the ir_value argument as a numeric value. The
device_virtual_dr_shift
takes the
dr_value
argument by either a binary string or a hexadecimal
string. Do not use numeric values for the
device_virtual_dr_shift
.
Note:
Running a DR Shift Operation Through a Virtual JTAG Chain
A simple DR shift operation through a virtual JTAG chain using an Altera download cable consists of the
following steps:
1. Query for the Altera programming cable and select the active cable.
2. Target the desired device in the JTAG chain.
3. Obtain a device lock for exclusive communication to the device.
4. Perform a VIR shift.
5. Perform a VDR shift.
6. Release exclusive link with the device with the
device_unlock command.
7. Close communication with the device with the close_device command.
Run-Time Communication without Using an Altera Programming Cable
The Virtual JTAG megafunction Tcl API requires an Altera programming cable. Designs that use a custom
controller to drive the JTAG chain directly must issue the correct JTAG IR/DR transactions to target the
Virtual JTAG megafunction instances. The address values and register length information for each Virtual
JTAG megafunction instance are provided in the compilation reports.
The following figure shows the compilation report for a Virtual JTAG megafunction Instance. The following
table describes each column in the Virtual JTAG Settings compilation report.
Altera Corporation Virtual JTAG Megafunction (sld_virtual_jtag)
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17 Running a DR Shift Operation Through a Virtual JTAG Chain
UG-SLDVRTL
2014.03.19