Serial Wire Debug The Serial Wire Debug (SWD) mode is an alternative to the standard JTAG interface. It uses only two pins to provide the same debug functionality as JTAG with no performance penalty, and introduces data trace capabilities with the. The SWD interface pins can be overlaid with JTAG signals, allowing the standard target to be used:. TCLK - SWCLK (Serial Wire Clock). TMS - SWDIO (Serial Wire Data Input/Output).
TDO - SWO (Serial Wire Output - required for ) JTAG and SWD modes are fully supported by, and. Serial Wire Viewer Cortex-M3, Cortex-M4, and Cortex-M7 based devices are able to provide high-speed data trace information in a number of ways depending on the type of information or analysis you require. The Serial Wire Serial (SWV) provides real-time data trace information from various sources within a Cortex-M3/M4/M7 device. It is transmitted via the SWO pin while your system processor continues to run at full speed.
Information is available from the ITM (Instrumentation Trace Macrocell) and DWT (Data Watchpoint and Trace) units, providing:. PC (Program Counter) sampling.
Event counters that show CPU cycle statistics. Exception and Interrupt execution with timing statistics. Trace data - data reads and writes used for timing analysis. ITM trace information used for simple printf-style debugging SWV data trace is available via the SWO pin in two output formats:. UART style (1Mb/s) - supported by and.
Manchester encoded (100Mb/s) - supported.
This specification describes the registers and data structures used to interface with the USB Type-C connectors on a system. The system software component is referred to as the OS Policy Manager (OPM) in this specification. This specification is intended for hardware component designers, system builders and device driver (software) developers. The reader is expected to be familiar with USB Type-C and USB Power Delivery (PD) specifications. In spite of due diligence, there may exist conflicts between this specification and either one or both of the above mentioned specifications. In such cases the USB Type-C and USB Power Delivery (PD) take precedence.
Adopters can demonstrate compliance of their product(s) with the.: Provides strategies for BIOS implementation of UCSI and includes reference documents and common terminology. USB 2.0 (download from the USB-IF website): Technical details necessary to understand USB 2.0 requirements and to design USB 2.0-compatible products. These specifications address the need for portable devices to communicate with each other and with USB peripherals when a PC is not available. The EHCI compliance testing program measures an EHCI controller implementation for conformance to the EHCI specification and evaluates the functionality of the EHCI controller function of a USB 2.0 host controller.
It does not evaluate the functionality of the USB companion controllers. The UTMI specification covers the physical interface and many operational aspects of the USB 2.0 Transceiver Macrocell (UTM). The intent of the UTMI is to accelerate USB 2.0 High-speed, Full-speed, and Low-speed peripheral development.
This document defines an interface to which ASIC and peripheral vendors can develop. ASIC vendors and foundries will implement the UTM and add it to their device libraries. Peripheral and IP vendors will be able to develop their designs, insulated from the high-speed and analog circuitry issues associated with the USB 2.0 interface, thus minimizing the time and risk of their development cycles.
Debug Architecture provides a standardized infrastructure for deeply in the mobile and mobile-influenced space. The MIPI Debug Working Group released therefore a portfolio of specifications. Their objective is to provide standard debug protocols and standard interfaces from the to the debug tool. The whitepaper Architecture Overview for Debug summarizes all efforts. In the last years the group focused on specifying protocols that improve the visibility of internal operations in deeply embedded systems, standardizing debug solutions via the functional interfaces of devices and specifying the use of I3C as debug bus.
Contents. King of the hill wav file. The term 'debug' The term debug is used as an inclusive way to encompass the various methods used to detect, triage, trace, and potentially eliminate mistakes, or bugs, in hardware and/or software. Debug includes control/configure methods, stop/step mode debugging, and various forms of trace.
Control/configure methods Debug can be used to control and/or configure components, including embedded systems, of a given target system. Common functions include setting up hardware breakpoints, configuring watchpoints, preparing and configuring the trace system, and examining system states. Stop/step mode debugging In stop/step mode debugging, the core/microcontroller is stopped through the use of breakpoints. This can be used to “step” through the code. If the other cores/microcontrollers of the SoC are stopped synchronously, the overall state of the system can be examined without worrying that things may change underfoot. Stop/step mode debugging includes control/configure techniques (as given previously), run control of a core/microcontroller, start-/stop synchronization with other cores, memory and register access and additional debug features such as performance counter, run-time memory access. Tracing Traces allow an in-depth analysis of the behavior and the timing characteristics of an embedded system.
The following trace sources typically generate trace data:. A core trace provides detailed visibility of the program execution on an embedded core. Trace data are generated for the instruction execution sequence (sometimes referred to as instruction trace) and/or data transfers (sometimes referred to as data trace). A SoC may contain several core traces. A bus trace provides detailed visibility on the data transfers on a specific bus. A system trace provides visibility of various events/states inside the embedded system.
Trace data can be generated by instrumented application code and/or by hardware modules within the SoC. A SoC may contain several system traces. Visibility of SoC-internal operations. Layering of the trace specifications Tracing is the tool of choice to monitor and analyze what is going on in a complex SoC. There is a number of non-MIPI core trace and bus trace standards well established in the embedded market. Thus, there was no need for the MIPI Debug Working Group to specify new ones. But no standard existed for system trace, when the Debug Working Group published its first version of the MIPI System Trace Protocol (MIPI STP) in 2006.
MIPI System Software Trace (MIPI SyS-T) The generation of system trace data from software is typically done by inserting additional function calls, which produce diagnostic information valuable for the debug process. This debug technique is called instrumentation.
Examples are: printf-style string generating functions, value information, assertions etc. The purpose of the MIPI System Software Trace is to define a reusable, general purpose data protocol and instrumentation API for debug. The specification defines message formats, which allow a trace analysis tool to decode the debug messages either to human-readable text or to messages optimized for an automated analysis. Since verbose textual messages are stressing bandwidth limits for debug, so-called catalog messages are provided.
Catalog messages are compact binary messages that replace strings with numeric values. The translation from this value to the verbose message is done by the trace receiving analysis tool with the help of XML collateral information. This information is provided by the software build process using an XML schema that is part of the specification as well.
The SyS-T data protocol is designed to work efficiently on top of lower level transport links like the MIPI System Trace Protocol. SyS-T protocol features like timestamping or data integrity checksums can be disabled, if the transport link already provides such capabilities. Other transport links, such as UART, USB or TCP/IP are also possible. The MIPI Debug Working Group will provide an open source reference implementation for the SyS-T instrumentation API, a SyS-T message pretty printer, and a tool to generate the XML collateral data as soon as the Specification for System Software Trace (SyS-T) is approved. MIPI System Trace Protocol (MIPI STP).
The MIPI System Trace Protocol specifies a generic protocol, that allows to merge trace streams originated from anywhere in the SoC to a trace stream of 4-bit frames. It was intentionally designed to merge system trace information. The MIPI System Trace Protocol uses a channel/master topology that allows the trace receiving analysis tool to collate the individual trace streams for analysis and display. The protocol provides additionally the following features: stream synchronization and alignment, trigger markers, global timestamping and multiple stream time synchronization.
The stream of STP packets produced by the System Trace Module can be directly saved to a trace RAM, directly exported off-chip or can be routed to a TWP module to merge it with further trace streams. ARM´s CoreSight System Trace Macrocell which is compliant with MIPI STP is today an integral part of most multi-core chips used in the mobile space.
The last MIPI board adopted version of Specification for System Trace Protocol (STP SM) is version 2.2 (February 2016). MIPI Trace Wrapper Protocol (MIPI TWP) The MIPI Trace Wrapper Protocol enables multiple trace streams to be merged into a single trace stream (byte streams). A unique ID is assigned to each trace stream by a wrapping protocol. The detection of byte/word boundaries is possible even if the data is transmitted as a stream of bits. Inert packets are used if a continuous export of trace data is required.
MIPI Trace Wrapper Protocol is based on ARM´s Trace Formatter Protocol specified for ARM CoreSight. The last MIPI board adopted version of Specification for Trace Wrapper Protocol (TWP SM) is version 1.1 (December 2014). From dedicated to functional interfaces. In the early stages of product development, it is common to use development boards with dedicated and readily-accessible debug interfaces for connecting the debug tools.
SoCs employed in the mobile market rely on two debug technologies: stop mode debugging via a scan chain and stop mode debugging via memory-mapped debug registers. The following non-MIPI debug standards are well established in the embedded market: IEEE 1149.1 (5-pin) and ARM Serial Wire Debug (2-pin), both using single-ended pins. Thus, there was no need for the MIPI Debug Working Group to specify a stop mode debug protocol or to specify a debug interface. Trace data generated and merged to a trace stream within the SoC can be streamed via a dedicated unidirectional trace interface off-chip to a trace analysis tool.
The MIPI Debug Architecture provides specifications for both, parallel and serial trace ports. The MIPI Parallel Trace Interface (MIPI PTI) specifies how to pass the trace data to multiple data and a clock pin (single-ended). The specification includes: signal names and functions, timing and electrical constraints. The last MIPI board adopted version of Specification for Parallel Trace Interface is version 2.0 (October 2011). The MIPI High-Speed Trace Interface (MIPI HTI) specifies how to stream trace data over the physical layer of standard interfaces such as PCI Express, Display Port, HDMI or USB. The current version of the spec. Allows one to six lanes.
The specification includes:. The LINK layer, which defines how the trace is packaged into the Aurora 8B/10B protocol. The PHY layer, which defines the electrical and clocking characteristics of the serial lanes. A programmer’s model for controlling HTI and providing status information. 34-pin board level connector HTI is a subset of the High Speed Serial Trace Port (HSSTP) specification defined by ARM Limited.
The last MIPI board adopted version of Specification for High-speed Trace Interface is version 1.0 (July 2016). Board developers and debug tools vendors benefit from standard debug connectors and standard pin mappings. The MIPI Recommendation for Debug and Trace Connectors recommends 10-/20-/34-pin board-level connectors (1.27 mm 050').
Seven different pin mappings are specified that address a wide variety of debug scenarios. They include: standard JTAG (IEEE 1149.1), cJTAG (IEEE 1149.7) and 4-bit parallel trace interface (mainly used for system traces). Supplemented by the ARM-specific standard SWD (Serial Wire Debug) MIPI10/20/34 debug connector became the standard debug connectors for ARM-based embedded designs. Many embedded designs in the mobile space use high-speed parallel trace ports (up to 600 Mbit/s/pin).
MIPI recommends a 60-pin Samtec QSH/QTH connector named MIPI60. It allows JTAG/cJTAG for run control, up to 40 trace data signals and up to 4 trace clocks. To minimize complexity, the recommendation defines four standard configurations with one, two, three or four trace channels of varying width. The last MIPI board adopted version of MIPI Alliance Recommendation for Debug and Trace Connectors is version 1.1 (March 2011). PHY and pin overlaid interfaces.
USB Type-C Mux switches USB2 pins to SWD pins Readily-accessible debug interfaces are not available at the product’s final form factor. This hampers the identification of bugs and performance optimization in the end product. Since the debug logic is still present in the end product, an alternative access path is needed. An effective way is to equip a mobile terminal´s standard interface with a multiplexer that allows accessing the debug logic.
Serial Wire Debug
The switching between the interface´s native function and the debug function can be initiated by the connected debug tool or by the mobile terminal’s software. Standard debug tools can be used under the following conditions:. A debug adapter exits that connects the debug tool to the standard interface. The debug adapter has to assist the switching protocol if required. A switching protocol is implemented on the debug tool and in the mobile terminal. A mapping from the standard interface pins to the debug pins is specified. The MIPI Narrow Interface for Debug and Test (MIPI NIDnT) covers debugging via the following standard interfaces: microSD, USB 2.0 Micro-B/-AB receptacle, USB Type-C receptacle, and Display Port.
The last MIPI board adopted version of Specification for Narrow Interface for Debug and Test (NIDnT SM) is version 1.1 (January 2016). Network interfaces. Instead of re-using the pins, debugging can also be done via the protocol stack of a standard interface or network.
Here debug traffic co-exists with the traffic of other applications using the same communication link. The MIPI Debug Working Group named this approach GigaBit Debug. Since no debug protocol existed for this approach, the MIPI Debug Working Group specified its SneakPeak debug protocol.
MIPI SneakPeek Protocol (MIPI SPP) opened up a path away from a dedicated interface for basic debug towards a protocol-driven interface. It translates incoming command packets into read/write accesses to memory, memory-mapped debug registers and other memory-mapped system resources. It translates command results (status information and read data coming from memory, memory-mapped debug registers and other memory-mapped system resources) to outgoing response packets. Since SneakPeek accepts packets coming through an input buffer and delivers packets through an output buffer it can be easily connected to any standard I/O or network.
The MIPI Alliance Specification for SneakPeek Protocol describes the basic concepts, the required infrastructure, the packets and the data flow. The last MIPI board adopted version of Specification for SneakPeek Protocol (SPP SM) is version 1.0 (August 2015). The MIPI Gigabit Debug Specification Family is providing details for mapping debug and trace protocols to standard I/Os or networks available in mobile terminals. These details include (not an exhaustive list): endpoint addressing, link initialization and management, data packaging, data flow management and error detection and recovery.
The last MIPI board adopted version of Specification for Gigabit Debug for USB is version 1.0 (August 2015). The last MIPI board adopted version of Specification for Gigabit Debug for Internet Protocol Sockets is version 1.0 (July 2016). I3C as debug bus Current debug solutions, such as JTAG and ARM CoreSight, are statically structured which leads to limited scalability regarding the accessibility of debug components/devices. MIPI Debug for I3C specifies a scalable, 2-pin, single-ended debug solution, which has the advantage that it is available for the entire product lifetime.
I3C can be used as debug bus only or can be shared between debug and its native function as data acquisition bus for sensors. Debugging via I3C works in principal as follows:. The I3C bus is used for the physical transport and the native I3C functionality is used to configure the bus and to hot join new components. The debug protocol is wrapped into dedicated I3C CCC commands. Supported debug protocols are JTAG, ARM CoreSight and Intel EXI.
The data acquisition function of the I3C Slaves is bridged to debug functionality. References.
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This article needs additional citations for. Unsourced material may be challenged and removed. (November 2009) For the Xbox 360 hack, see. JTAG (named after the Joint Test Action Group which codified it) is an for verifying designs and testing after manufacture. JTAG implements standards for on-chip instrumentation in (EDA) as a complementary tool to. It specifies the use of a dedicated debug port implementing a interface for low-overhead access without requiring direct external access to the system address and data buses.
The interface connects to an on-chip test access port (TAP) that implements a protocol to access a set of test registers that present chip logic levels and device capabilities of various parts. The Joint Test Action Group formed in 1985 to develop a method of verifying designs and testing after manufacture. In 1990 the codified the results of the effort in IEEE Standard 1149.1-1990, entitled Standard Test Access Port and Boundary-Scan Architecture. The JTAG standards have been extended by many semiconductor chip manufacturers with specialized variants to provide vendor-specific features. Contents.
History In the 1980s, multi-layer circuit boards and non-lead-frame (ICs) were becoming standard and connections were being made between ICs that were not available to probes. The majority of manufacturing and field faults in circuit boards were due to poor joints on the boards, imperfections among board connections, or the bonds and bond wires from IC pads to pin lead frames. The Joint Test Action Group (JTAG) was formed in 1985 to provide a pins-out view from one IC pad to another so these faults could be discovered. The industry standard became an standard in 1990 as IEEE Std. 1149.1-1990 after many years of initial use. In the same year, released their first with JTAG (the ) which led to quicker industry adoption by all manufacturers.
In 1994, a supplement that contains a description of the (BSDL) was added. Further refinements regarding the use of all-zeros for EXTEST, separating the use of SAMPLE from PRELOAD and better implementation for OBSERVEONLY cells were made and released in 2001. Since 1990, this standard has been adopted by companies around the world. Is now mostly synonymous with JTAG, but JTAG has essential uses beyond such manufacturing applications.
Debugging Although JTAG's early applications targeted board level testing, the JTAG standard was designed to assist with device, board, and system testing, diagnosis, and fault isolation. Today JTAG is used as the primary means of accessing sub-blocks of, making it an essential mechanism for which may not have any other debug-capable communications channel. On most systems, JTAG-based debugging is available from the very first instruction after CPU reset, letting it assist with development of early boot software which runs before anything is set up.
An (or, more correctly, a 'JTAG adapter') uses JTAG as the transport mechanism to access on-chip modules inside the target. Those modules let software developers debug the software of an directly at the machine instruction level when needed, or (more typically) in terms of high level language source code.
System software debug support is for many software developers the main reason to be interested in JTAG. Many silicon architectures such as PowerPC, MIPS, ARM, x86 built an entire software debug, instruction tracing, and data tracing infrastructure around the basic JTAG protocol. Frequently individual silicon vendors however only implement parts of these extensions.
Some examples are ARM and as well as Intel's BTS (Branch Trace Storage), LBR (Last Branch Record), and IPT (Intel Processor Trace) implementations. There are many other such silicon vendor-specific extensions that may not be documented except under. The adoption of the JTAG standard helped move JTAG-centric debugging environments away from early processor-specific designs. Processors can normally be halted, single stepped, or let run freely. One can set code breakpoints, both for code in RAM (often using a special machine instruction) and in ROM/flash. Data breakpoints are often available, as is bulk data download to RAM. Most designs have “halt mode debugging”, but some allow debuggers to access registers and data buses without needing to halt the core being debugged.
Serial Debug Cable
Some toolchains can use ARM Embedded Trace Macrocell (ETM) modules, or equivalent implementations in other architectures to trigger debugger (or tracing) activity on complex hardware events, like a programmed to ignore the first seven accesses to a register from one particular subroutine. Sometimes developers also use JTAG to develop debugging tools.
The same JTAG techniques used to debug software running inside a can help debug other digital design blocks inside an FPGA. For example, custom JTAG instructions can be provided to allow reading registers built from arbitrary sets of signals inside the FPGA, providing visibility for behaviors which are invisible to boundary scan operations. Similarly, writing such registers could provide controllability which is not otherwise available. Storing firmware JTAG allows to transfer data into internal non-volatile device memory (e.g. Some device programmers serve a double purpose for programming as well as debugging the device. In the case of FPGAs, volatile memory devices can also be programmed via the JTAG port, normally during development work. In addition, internal monitoring capabilities (temperature, voltage and current) may be accessible via the JTAG port.
JTAG programmers are also used to write software and data into. This is usually done using data bus access like the CPU would use, and is sometimes actually handled by a CPU, but in other cases memory chips have JTAG interfaces themselves. Some modern debug architectures provide internal and external bus master access without needing to halt and take over a CPU. In the worst case, it is usually possible to drive external bus signals using the boundary scan facility. As a practical matter, when developing an embedded system, emulating the instruction store is the fastest way to implement the 'debug cycle' (edit, compile, download, test, and debug).
This is because the in-circuit emulator simulating an instruction store can be updated very quickly from the development host via, say, USB. Using a serial UART port and bootloader to upload firmware to Flash makes this debug cycle quite slow and possibly expensive in terms of tools; installing firmware into Flash (or SRAM instead of Flash) via JTAG is an intermediate solution between these extremes. Boundary scan testing JTAG technology provides access to many logic signals of a complex integrated circuit, including the device pins. The signals are represented in the boundary scan register (BSR) accessible via the TAP. This permits testing as well as controlling the states of the signals for testing and debugging.
Therefore, both software and hardware (manufacturing) faults may be located and an operating device may be monitored. When combined with built-in self-test , the JTAG scan chain enables a low overhead, embedded solution to testing an IC for certain static faults (shorts, opens, and logic errors). The scan chain mechanism does not generally help diagnose or test for timing, temperature or other dynamic operational errors that may occur. Are often provided in standardized formats such as, or its binary sibling XSVF, and used in production tests. The ability to perform such testing on finished boards is an essential part of in today's products, increasing the number of faults that can be found before products ship to customers.
Electrical characteristics A JTAG interface is a special interface added to a chip. Depending on the version of JTAG, two, four, or five pins are added. The four and five pin interfaces are designed so that multiple chips on a board can have their JTAG lines together if specific conditions are met. The two pin interface is designed so that multiple chips can be connected in a. In either case a need only connect to a single 'JTAG port' to have access to all chips on a. Daisy-chained JTAG (IEEE 1149.1). The connector pins are:.
TDI (Test Data In). TDO (Test Data Out). TCK (Test Clock). TMS (Test Mode Select). TRST (Test Reset) optional.
The TRST pin is an optional active-low reset to the test logic, usually asynchronous, but sometimes synchronous, depending on the chip. If the pin is not available, the test logic can be reset by switching to the reset state synchronously, using TCK and TMS.
Note that resetting test logic doesn't necessarily imply resetting anything else. There are generally some processor-specific JTAG operations which can reset all or part of the chip being debugged. Since only one data line is available, the protocol is.
Foxit phantompdf 6.2 cracked. The clock input is at the TCK pin. One bit of data is transferred in from TDI, and out to TDO per TCK rising clock edge. Different instructions can be loaded.
Instructions for typical ICs might read the chip ID, sample input pins, drive (or float) output pins, manipulate chip functions, or bypass (pipe TDI to TDO to logically shorten chains of multiple chips). As with any clocked signal, data presented to TDI must be valid for some chip-specific Setup time before and Hold time after the relevant (here, rising) clock edge. TDO data is valid for some chip-specific time after the falling edge of TCK. The maximum operating frequency of TCK varies depending on all chips in the chain (the lowest speed must be used), but it is typically 10-100 MHz (100-10 ns per bit).
Also TCK frequencies depend on board layout and JTAG adapter capabilities and state. One chip might have a 40 MHz JTAG clock, but only if it is using a 200 MHz clock for non-JTAG operations; and it might need to use a much slower clock when it is in a low power mode.
Accordingly, some JTAG adapters have adaptive clocking using an RTCK (Return TCK) signal. Faster TCK frequencies are most useful when JTAG is used to transfer lots of data, such as when storing a program executable into. Clocking changes on TMS steps through a standardized JTAG. The JTAG state machine can reset, access an instruction register, or access data selected by the instruction register. JTAG platforms often add signals to the handful defined by the IEEE 1149.1 specification. A System Reset (SRST) signal is quite common, letting debuggers reset the whole system, not just the parts with JTAG support.
Sometimes there are event signals used to trigger activity by the host or by the device being monitored through JTAG; or, perhaps, additional control lines. Even though few consumer products provide an explicit JTAG port connector, the connections are often available on the as a remnant from development and/or production. When exploited, these connections often provide the most viable means for. Reduced pin count JTAG (IEEE 1149.7). Example of JTAG with reduced pin count Reduced pin count JTAG uses only two wires, a clock wire and a data wire. This is defined as part of the IEEE 1149.7 standard. The connector pins are:.
TMSC (Test Serial Data). TCKC (Test Clock) It is called cJTAG for compact JTAG. The two wire interface reduced pressure on the number of pins, and devices can be connected in a.
The star topology enables some parts of the system to be powered down, while others can still be accessed over JTAG; a daisy chain requires all JTAG interfaces to be powered. Other two-wire interfaces exist, such as. Communications model In JTAG, devices expose one or more test access ports (TAPs).
The picture above shows three TAPs, which might be individual chips or might be modules inside one chip. A daisy chain of TAPs is called a scan chain, or (loosely) a target.
Scan chains can be arbitrarily long, but in practice twenty TAPs is unusually long. To use JTAG, a host is connected to the target's JTAG signals (TMS, TCK, TDI, TDO, etc.) through some kind of JTAG adapter, which may need to handle issues like level shifting and. The adapter connects to the host using some interface such as USB, PCI, Ethernet, and so forth. Primitives The host communicates with the TAPs by manipulating TMS and TDI in conjunction with TCK, and reading results through TDO (which is the only standard host-side input). TMS/TDI/TCK output transitions create the basic JTAG communication primitive on which higher layer protocols build:.
State switching. All TAPs are in the same state, and that state changes on TCK transitions. This JTAG state machine is part of the JTAG spec, and includes sixteen states.
There are six “stable states” where keeping TMS stable prevents the state from changing. In all other states, TCK always changes that state. In addition, asserting TRST forces entry to one of those stable states (TestLogicReset), in a slightly quicker way than the alternative of holding TMS high and cycling TCK five times. Most parts of the JTAG state machine support two stable states used to transfer data. Each TAP has an instruction register (IR) and a data register (DR).
The size of those registers varies between TAPs, and those registers are combined through TDI and TDO to form a large shift register. (The size of the DR is a function of the value in that TAP's current IR, and possibly of the value specified by a SCANN instruction.) There are three operations defined on that shift register:. Capturing a temporary value. Entry to the ShiftIR stable state goes via the CaptureIR state, loading the shift register with a partially fixed value (not the current instruction).
Entry to the ShiftDR stable state goes via the CaptureDR state, loading the value of the Data Register specified by the TAP's current IR. Shifting that value bit-by-bit, in either the ShiftIR or ShiftDR stable state; TCK transitions shift the shift register one bit, from TDI towards TDO, exactly like a mode 1 data transfer through a daisy chain of devices (with TMS=0 acting like the chip select signal, TDI as MOSI, etc.).
Updating IR or DR from the temporary value shifted in, on transition through the UpdateIR or UpdateDR state. Note that it is not possible to read (capture) a register without writing (updating) it, and vice versa. A common idiom adds flag bits to say whether the update should have side effects, or whether the hardware is ready to execute such side effects. One stable state is called RunTest/Idle. The distinction is TAP-specific.
Single Wire Debug
Clocking TCK in the Idle state has no particular side effects, but clocking it in the RunTest state may change system state. For example, some cores support a debugging mode where TCK cycles in the RunTest state drive the instruction pipeline. So at a basic level, using JTAG involves reading and writing instructions and their associated data registers; and sometimes involves running a number of test cycles. Behind those registers is hardware that is not specified by JTAG, and which has its own states that is affected by JTAG activities. Most JTAG hosts use the shortest path between two states, perhaps constrained by quirks of the adapter.
(For example, one adapter only handles paths whose lengths are multiples of seven bits.) Some layers built on top of JTAG monitor the state transitions, and use uncommon paths to trigger higher level operations. Some ARM cores use such sequences to enter and exit a two-wire (non-JTAG) mode. A Zero Bit Scan (ZBS) sequence is used in IEEE 1149.7 to access advanced functionality such as switching TAPs into and out of scan chains, power management, and a different two-wire mode. JTAG IEEE Std 1149.1 (boundary scan) instructions Instruction register sizes tend to be small, perhaps four or seven bits wide. Except for BYPASS and EXTEST, all instruction opcodes are defined by the TAP implementor, as are their associated data registers; undefined instruction codes should not be used.
Two key instructions are:. The BYPASS instruction, an opcode of all ones regardless of the TAP's instruction register size, must be supported by all TAPs. The instruction selects a single bit data register (also called BYPASS). The instruction allows this device to be bypassed (do nothing) while other devices in the scan path are exercised. The optional IDCODE instruction, with an implementor-defined opcode.
IDCODE is associated with a 32-bit register (IDCODE). Its data uses a standardized format that includes a manufacturer code (derived from the Standard Manufacturer's Identification Code standard, JEP-106), a part number assigned by the manufacturer, and a part version code. IDCODE is widely, but not universally, supported. On exit from the RESET state, the instruction register is preloaded with either BYPASS or IDCODE. This allows JTAG hosts to identify the size and, at least partially, contents of the scan chain to which they are connected. (They can enter the RESET state then scan the Data Register until they read back the data they wrote. A BYPASS register has only a zero bit; while an IDCODE register is 32-bits and starts with a one.
So the bits not written by the host can easily be mapped to TAPs.) Such identification is often used to sanity check manual configuration, since IDCODE is often unspecific. It could for example identify an ARM Cortex-M3 based microcontroller, without specifying the microcontroller vendor or model; or a particular FPGA, but not how it has been programmed. A common idiom involves shifting BYPASS into the instruction registers of all TAPs except one, which receives some other instruction. That way all TAPs except one expose a single bit data register, and values can be selectively shifted into or out of that one TAP's data register without affecting any other TAP. The IEEE 1149.1 (JTAG) standard describes a number of instructions to support boundary scan applications. Some of these instructions are 'mandatory', but TAPs used for debug instead of boundary scan testing sometimes provide minimal or no support for these instructions.
A Netgear DG632 with an 8 pin JTAG header at location '5'. There are no official standards for JTAG adapter physical connectors. Development boards usually include a header to support preferred development tools; in some cases they include multiple such headers, because they need to support multiple such tools. For example, a microcontroller, FPGA, and ARM application processor rarely shares tools, so a development board using all of those components might have three or more headers. Production boards may omit the headers; or when space is tight, just provide JTAG signal access using test points. Neal Stollon (2011).
On-Chip Instrumentation. Copies of or its 2001 update may be bought from the IEEE. ^. presents one of the models for such tools. ^ Texas Instruments is one adopter behind this standard, and has an with more information.
Oshana, Rob (29 October 2002). Embedded Systems Design. Retrieved 5 April 2007.
revision r1p5, ARM DDI 0211K. Chapter 14 presents the Debug TAP. Other ARM11 cores present the same model through their Debug TAPs.
Documentation for the OMAP2420 is not publicly available. However, a document discussing a JTAG diagnostic tool presents this OMAP2420 scan chain example (and others).
See 'i.MX35 (MCIMX35) Multimedia Applications Processor Reference Manual' from the web site. Chapter 44 presents its 'Secure JTAG Controller' (SJC). revision r1p2. Appendix B 'Debug in Depth' presents the EmbeddedICE-RT module, as seen in the popular ARM926ejs core. AN1817/D, 'MMC20xx M.CORE OnCE Port Communication and Control Sequences'; Freescale Semiconductor, Inc.; 2004.
Not all processors support the same OnCE module. AN2073 'Differences Between the EOnCE and OnCE Ports'; Freescale Semiconductor, Inc.; 2005. lists a few JTAG-only header layouts that have widespread tool support.
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Retrieved 2017-08-10. External links.
The official IEEE 1149.7 Standard. Intel whitepaper on JTAG usage in system software debug across a wide range of architectures. Includes a strong technical presentation about JTAG, with design-for-test chapters. including details of variants of the IEEE standard, BSDL, DFT, and other topics. Useful tutorials and information on JTAG technology.
Useful information on JTAG, timeline, architecture and more. JTAG for product development, life cycle, testing, tools needed, and other topics. Information on the Xbox 360 JTAG hack.
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