Capturing the virtual ir instruction register – Altera Virtual JTAG IP Core User Manual

Page 32

Table 14: SLD_NODE_INFO Register Descriptions

Function

Field

Identifies the version of the SLD node

Node Version

Identifies the type of NODE IP (0x8 for the Virtual JTAG megafunction)

NODE ID

SLD Node Manufacturer ID (0x6E for Virtual JTAG megafunction)

NODE MFG_ID

Used to distinguish multiple instances of the same IP. Corresponds to
the instance index assigned in the MegaWizard Plug-In Manager.

NODE_INST_ID

You can identify each Virtual JTAG instance within the design by decoding NODE ID and

NODE_INST_ID

The Virtual JTAG megafunction uses a NODE ID of 8. The

NODE_INST_ID

corresponds to the instance index

that you configured within the MegaWizard Plug-In Manager. The

ADDR

bits for each Virtual JTAG node

is then determined by matching each Virtual JTAG instance to the sequence number in which the

SLD_NODE_INFO

Capturing the Virtual IR Instruction Register

In applications that contain multiple SLD nodes, capturing the value of the VIR may require issuing an
instruction to the SLD hub to target a SLD node. You can query for a VIR using the

VIR_CAPTURE

instruction.

Each SLD NODE VIR register acts as a parallel hold rank register to the USER1 DR chain. The sld_hub uses
the bits prepended to the VIR shift value to target the correct SLD NODE VIR register. After the

SLD_state_machine

asserts

virtual_update_IR

, the active SLD node latches

VIR_VALUE

of the USER1 DR

The figure below shows a functional model of the interaction of the USER1 DR register and the SLD node
VIR. The ADDR bits target the selection muxes in the figure after the sld_hub FSM has exited the

virtual_update_IR

state. Upon the next USER1 DR transaction, the USER1 DR chain will latch the VIR

of the last active SLD_NODE to shift out of

TDO

. Thus, if you need to capture the VIR of an SLD node that

is different than the one addressed in the previous shift cycle, you must issue the

VIR_CAPTURE

instruction.

The

VIR_CAPTURE

instruction to the sld_hub acts as an address cycle to force an update to the muxes.

Virtual JTAG Megafunction (sld_virtual_jtag)

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Capturing the Virtual IR Instruction Register

2014.03.19