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

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.

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.

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.