Examples Of Using The Once; Whether The Chip Has Entered The Debug Mode; Polling The Jtag Instruction Shift Register - Motorola DSP56305 User Manual

On-Chip Emulation Module

Examples of Using the OnCE

10.12 EXAMPLES OF USING THE OnCE
Following are some examples of debugging procedures. All these examples assume that
the DSP is the only device in the JTAG chain. If there is more than one device in the chain
(additional DSPs or other devices), the other devices can be forced to execute the JTAG
BYPASS instruction such as their effect in the serial stream will be one bit per additional
device. The events such as select-DR, select-IR, update-DR, and shift-DR refer to
bringing the JTAG TAP in the corresponding state. Please refer to Section 11 (JTAG), for
a detailed description of the JTAG protocol.
10.12.1 Checking Whether the Chip has Entered the Debug Mode
There are two methods to verify that the chip has entered the Debug mode:
1. Every time the chip enters the Debug mode, a pulse is generated on the DE signal.
A pulse is also generated every time the chip acknowledges the execution of an
instruction while in Debug mode. An external command controller can connect
the DE line to an interrupt signal in order to sense the acknowledge.
2. An external command controller can poll the JTAG instruction shift register for
the status bits OS[1:0]. When the chip is in Debug mode, these bits are set to the
value 11.
Note: In the following paragraphs, the ACK notation denotes the operation
performed by the command controller to check whether the Debug mode has
been entered (either by sensing DE or by polling JTAG instruction shift
register).

10.12.2 Polling the JTAG Instruction Shift Register

In order to poll the core status bits in the JTAG Instruction Shift register the following
sequence must be performed:
1. Select shift-IR. Passing through capture-IR loads the core status bits into the
instruction shift register.
2. Shift in ENABLE_ONCE. While shifting-in the new instruction the captured
status information is shifted-out. Pass through update-IR.
3. Return to Run-Test/Idle.
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