If Multiple TAP has the same IDCODE, aji_openocd can only access SLD nodes on the first TAP in the chain

[cinlyooi-intel]

If, in your JTAG chain, you have more than one TAP with the same IDCODE, you can only access SLD nodes on the first chain.

For example, you have two identical Altera FPGA chip, say S10s, on the jtag chain. Both has one Nios V on it, you can only access the NiosV on the first TAP on the jtag chain. While OpenOCD will give you two ports, both ports refers to the NiosV on the first TAP.

For avoidance of doubt, you can access all the NiosVs on the first TAP.

[cinlyooi-intel]

The problem is, inside

• AJI_ERROR jtagservice_lock(const struct jtag_tap* const tap) [Called when OpenOCD wants to send vIR and vDR commands to SLD target]
• static bool vjtag_examine_chain_match_tap(struct vjtag_tap* vtap) [Called when OpenOCD checks whether vjtag/SLD targets exists at the initialization phase of OpenOCD]

Both call static AJI_ERROR jtagservice_device_index_by_idcode(const DWORD idcode, DWORD* tap_index) to find the "tap_index". As its name implied, it only examine and match "idcode", so if multiple TAP has the same "idcode", it will return the first one.

[cinlyooi-intel]

The best way to spot this bug is to look at OpenOCD initialization messages when it initialize the JTAG chain and the start of OpenOCD

"Virtual Tap/SLD node 0x08986E00 found at tap position 0 vtap position n"

when you have a NiosV instance that share the same SLD ID as your NiosV instance in your target TAP,

If not, OpenOCD should report that your NiosV instance is not found.