Updated 18 June 2003 -- Maintained by E. Hazen
Introduction
The ATLAS CSM Mini-Adapter provides an interface between the CSM-0 VME
module and up to 18 production-style mezzanine boards. In normal
operation JTAG access is provided to all connected mezzanine boards in a
chain. Unconnected mezzanine boards are bypassed by simple on-board
logic on the adapter. In case of mezzanine board or cable problems, the
JTAG chain may not work, and can be hard to diagnose.
This page describes a mechanism by which individual mezzanine boards
can be switched in and out of the JTAG chain under software control.
Block Diagram of Mini-Adapter Logic
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Implementation of this logic is limited by two "features" of the PCB:
1. There is no power-up reset logic on the board
2. There are no spare signals allocated for communication
amongst the 4 CPLDs.
Keeping in mind these limitations, we describe here one possible
implementation of special firmware for JTAG control of the
mini-adapter.
JTAG Programming
At power-up the adapter is in an undefined state. Execute the
following sequence of operations (4) times to reset it:
- Enter Shift-IR state
- Shift (4) times instruction code MEZZCTRL (B"10101"; unused by AMT-2/3)
- Exit Shift-IR to Update-IR
At this point the length of the instruction register may be measured
if desired by entering the Shift-IR state and writing a recognizable
pattern, and waiting to see if the pattern is returned after repeated
shifting. Before exiting via Update-IR, one must shift (4) time the
MEZZCTRL instruction.
To read the state of the mezz SENSE inputs and enable a specific set
of mezz card ports, perform the following sequence of operations:
- Enter Shift-DR state
- Shift out and record 20-bit value. This is the state of the
SENSE inputs.
- Shift in a desired mask value, with a '1' value in each
location corresponding to a mezz port which is to be enabled.
- Exit via Update-DR state
- Enter Shift-IR state
- Shift (4) times any code Not MEZZCTRL (i.e. B"00000")
- Exit Shift-IR to Update-IR
There are two unused bits in the mask register, positions 14 and 19.
The first bit shifted out is bit 19; the last bit shifted is bit 0;
At this point the JTAG chain will provide access only to the selected
mezz cards. If a port with a non-working mezz card is selected, no
data will be returned. One must begin again with the reset sequence
at the top to regain control of the adapter. The adapter will not
appear as a device in the JTAG chain unless the instruction code
B"10101" is entered in the Shift-IR state as described above.
References:
