Low cost emulation scheme implemented via clock control using JTAG controller in a scan environment

• US 5,812,562 A
• Filed: 11/15/1996
• Issued: 09/22/1998
• Est. Priority Date: 11/15/1996
• Status: Expired due to Term

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Baeg, Sanghyeon
• Primary Examiner(s): Beausoliel, Jr., Robert W.
• Assistant Examiner(s): Iqbal, Nadeem
• Application Number:
  US08/749,858
• Time in Patent Office: 676 Days
• Field of Search: 371/22.3, 371/22.6, 371/22.5, 371/22.31, 371/22.32, 371/22.36, 371/27.7, 371/22.1, 395/183.06, 395/183.15, 395/183.1, 395/500, 395/183.03, 395/183.19, 364/579
• US Class Current: 714/726
• CPC Class Codes: G01R 31/318552 Clock circuits details

Abstract

An integrated circuit includes a test port operating at a first clock speed and at least one functional logic block operating at a second clock speed which is faster than the first clock speed. A control register, formed by boundary scan cells, operates at the first clock speed and provides control inputs to the functional block to control emulation tasks. The control register is writable via a serial shift operation through the test port while the functional block is operating. The outputs of the control register which are being provided to the functional block are held constant during the serial shift operation. An observation register, formed by boundary scan cells, operates at the first clock speed, and is readable through the test port via a serial shift operation, while the functional block is operating. The observation register receives signals from the functional block indicating status of the functional block.

Claims

1. A method for operating an integrated circuit which includes at least one functional logic block operating with a system clock at a first clock speed and a test port operating with a test clock at a second clock speed, the second clock speed being lower than the first clock speed, the test port being controlled by a test controller external to the integrated circuit, the method comprising the steps of:

selecting as a scan address a first control register containing first control values being provided to the functional block, via the test port with a first test instruction;

shifting second control values into the first control register at the second clock speed, the first control values being provided to the functional logic block, not changing during the shifting;

loading the updated control values from a first portion into a second portion of the control register to provide the updated control values to the functional logic block;

wherein,

the second control values include a stop clock flag request bit, indicating to the functional logic that the test controller wishes to stop the system clocks, and wherein,

the second control values are shifted into the first control register while the system clock is being provided to the functional block, and wherein,

the functional logic responds to assertion of the stop clock flag request bit by going into an idle state by completion of pending instructions in an instruction stack and providing an idle signal to a second control register indicating that the functional logic has gone to the idle state.

2. A method as recited in claim 1 further comprising the steps of:

monitoring the state of the second control register through the test port to determine when the idle signal is asserted by the functional logic;

once the idle signal has been detected by the test controller, shifting and loading second control values, the third control values including a stop clocks control bit asserted to indicate to a clock control logic block, to stop system clocks, to thereby stop the system clocks.

3. A method for operating an integrated circuit which includes at least one functional logic block operating with a system clock at a first clock speed and a test port operating with a test clock at a second clock speed, the second clock speed being lower than the first clock speed, the test port being controlled by a test controller external to the integrated circuit, the method comprising the steps of:

selecting as a scan address a first control register containing first control values being provided to the functional block, via the test port with a first test instruction;

shifting second control values into the first control register at the second clock speed, the first control values being provided to the functional logic block, not changing during the shifting;

loading the updated control values from a first portion into a second portion of the control register to provide the updated control values to the functional logic block;

shifting and loading the first control register to specify a count value of the number of clock cycles which should be provided by a clock control logic circuit; and

executing the specified number of clock cycles at one of the first clock speed and the second clock speed according to control bits in the first control register.

4. An integrated circuit comprising:

a test port operating at a first clock speed;

at least one functional block operating at a second clock speed which is faster than the first clock speed;

a control register, formed by boundary scan cells, operating at the first clock speed, providing control inputs to the functional block to control emulation tasks of the functional block, the control register being writable via a serial shift operation through the test port while the functional block is operating, the outputs of the control register which are being provided to the functional block being constant during the serial shift operation;

an observation register, formed by boundary scan cells, operating at the first clock speed, which is readable through the test port via a serial shift operation, while the functional block is operating, the observation register receiving inputs indicating status of the functional block; and

wherein the control register includes a plurality of bits indicating a clock count, the clock count indicating to a clock control circuit to provide a number of clock cycles represented by the clock count, the control register further including bits provided to the clock control circuit, indicating whether the clock control circuit should issue the number of clock cycles at the first or second clock frequency.

5. An integrated circuit comprising:

a test port operating at a first clock speed;

at least one functional block operating at a second clock speed which is faster than the first clock speed;

a control register, formed by boundary scan cells, operating at the first clock speed, providing control inputs to the functional block to control emulation tasks of the functional block, the control register being writable via a serial shift operation through the test port while the functional block is operating, the outputs of the control register which are being provided to the functional block being constant during the serial shift operation;

an observation register, formed by boundary scan cells operating at the first clock speed, which is readable through the test port via a serial shift operation, while the functional block is operating, the observation register receiving inputs indicating status of the functional block;

a plurality of boundary scan strings, comprised of boundary scan cells, each cell receiving a mode signal as a multiplexer select signal; and

wherein

the control register includes a mode override control bit indicating to override test port mode control of the boundary scan strings, the control register further including mode control bits, one of the mode control bits being provided to each of the boundary scan strings to control the mode signal to each boundary scan string when the mode override control bit is asserted.