ARM1156T2-S™ Technical Reference Manual 14.5. The DBGTAP port and debug registers

14.5. The DBGTAP port and debug registers

The ARM1156T2-S DBGTAP controller is the part of the debug unit that enables access through the DBGTAP to the on-chip debug resources, such as breakpoint and watchpoint registers. The DBGTAP controller is based on the IEEE 1149.1 standard and supports:

a Device ID Register
a Bypass Register
a five-bit Instruction Register
a five-bit Scan Chain Select Register.

In addition, the public instructions listed in Table 14.1 are supported.

Table 14.1. Supported public instructions

Binary code	Instruction	Description
b00000	EXTEST	This instruction connects the selected scan chain between DBGTDI and DBGTDO. When the instruction register is loaded with the EXTEST instruction, the debug scan chains can be written. See Scan chains.
b00001	-	Reserved.
b00010	Scan_N	Selects the Scan Chain Select Register (SCREG). This instruction connects SCREG between DBGTDI and DBGTDO. See Scan Chain Select Register (SCREG).
b00011	-	Reserved.
b00100	Restart	Forces the processor to leave Debug state. This instruction is used to exit from Debug state. The processor restarts when the Run-Test/Idle state is entered.
b00101	-	Reserved.
b00110	-	Reserved.
b00111	-	Reserved.
b01000	Halt	Forces the processor to enter Debug state. This instruction is used to stop the integer unit and put it into Debug state.
b01001	-	Reserved.
b01010-b01011	-	Reserved.
b01100	INTEST	This instruction connects the selected scan chain between DBGTDI and DBGTDO. When the instruction register is loaded with the INTEST instruction, the debug scan chains can be read. See Scan chains.
b01101-b11100	-	Reserved.
b11101	ITRsel	When this instruction is loaded into the IR (Update-DR state), the DBGTAP controller behaves as if IR=EXTEST and SCREG=4. The ITRsel instruction makes the DBGTAP controller behave as if EXTEST and scan chain 4 are selected. It can be used to speed up certain debug sequences. See Using the ITRsel IR instruction for the effects of using this instruction.
b11110	IDcode	See IEEE 1149.1. Selects the DBGTAP controller device ID code register. The IDcode instruction connects the device identification register (or ID register) between DBGTDI and DBGTDO. The ID register is a 32-bit register that enables you to determine the manufacturer, part number, and version of a component using the DBGTAP. See Device ID Code Register for details of selecting and interpreting the ID register value.
b11111	Bypass	See IEEE 1149.1. Selects the DBGTAP controller bypass register. The Bypass instruction connects a 1-bit shift register (the bypass register) between DBGTDI and DBGTDO. The first bit shifted out is a 0. All unused DBGTAP controller instruction codes default to the Bypass instruction. See Bypass Register.

Note

Sample/Preload, Clamp, HighZ, and ClampZ instructions are not implemented because the ARM1156T2-S DBGTAP controller does not support the attachment of external boundary scan chains.

All unused DBGTAP controller instructions default to the Bypass instruction.

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