Background debug mode interface

Last updated

Background debug mode (BDM) interface is an electronic interface that allows debugging of embedded systems. Specifically, it provides in-circuit debugging functionality in microcontrollers. It requires a single wire and specialized electronics in the system being debugged. It appears in many Freescale Semiconductor products. Background commands are categorized into two types: Non-intrusive commands and Active background commands. Non-intrusive commands can be issued while the user program is running, which include memory access commands. [1]

Contents

The interface allows a Host to manage and query a target. Specialized hardware is required in the target device. No special hardware is required in the host; a simple bidirectional I/O pin is sufficient.

I/O signals

The signals used by BDM to communicate data to and from the target are initiated by the host processor. The host negates the transmission line, and then either

At the start of the next bit time, the host negates the transmission line, and the process repeats. Each bit is communicated in this manner.

In other words, the increasing complexity of today's software and hardware designs is leading to some fresh approaches to debugging. Silicon manufacturers offer more and more on-chip debugging features for emulation of new processors.

This capability, implemented in various processors under such names as background debug mode (BDM), JTAG and on-chip in-circuit emulation, puts basic debugging functions on the chip itself. With a BDM (1 wire interface) or JTAG (standard JTAG) debug port, you control and monitor the microcontroller solely through the stable on-chip debugging services.

This debugging mode runs even when the target system crashes and enables developers to continue investigating the cause of the crash.

Microcontroller application development

A good development tool environment is important to reduce total development time and cost. Users want to debug their application program under conditions that imitate the actual setup of their system. Because of that, the capability to debug a user program in an actual target system is required. This is known as in-circuit debugging. Furthermore, most new MCUs have nonvolatile memory such as flash memory so that programming code on the target system is also required. This is known as in-circuit programming.

To support in-circuit debugging and programming requirements, the HC08 Family has the monitor mode and the HCS08 and RS08 utilize a background debug mode (BDM). The background debug hardware on the HCS08 consists of a background debug controller (BDC) and debug module (DBG). The background debug hardware on the RS08 consists of the background debug controller (BDC) only.

BDM commands

The BDM host can issue commands with parameters to the target. Some commands allow reading or writing of blocks of the target's memory, individual registers in the CPU, or registers not available to the target.

Examples include:

BDM commands
READ_BYTERead a byte from memory
WRITE_BYTEWrite a byte to memory
GOStart/resume executing at current program counter location
WRITE_PCWrite a value to the program counter
READ_PCRead the value of the program counter
WRITE_XWrite a value to the index register
READ_XRead the value of the index register
READ_SPRead the value of the stack pointer

BDM functions

Depending on the target part, the BDM controller may feature a hardware breakpoint register. The register holds a value indicating an address in memory. When the target part's CPU accesses that location in memory, the BDM hardware can take control of the target part, stop program execution, and begin operating in background mode.

Related Research Articles

<span class="mw-page-title-main">Motorola 68HC11</span> 8-bit microcontroller family

The 68HC11 is an 8-bit microcontroller family introduced by Motorola Semiconductor in 1984. It descended from the Motorola 6800 microprocessor by way of the 6801. The 68HC11 devices are more powerful and more expensive than the 68HC08 microcontrollers and are used in automotive applications, barcode readers, hotel card key writers, amateur robotics, and various other embedded systems. The MC68HC11A8 was the first microcontroller to include CMOS EEPROM.

<span class="mw-page-title-main">Microcontroller</span> Small computer on a single integrated circuit

A microcontroller or microcontroller unit (MCU) is a small computer on a single integrated circuit. A microcontroller contains one or more CPUs along with memory and programmable input/output peripherals. Program memory in the form of ferroelectric RAM, NOR flash or OTP ROM is also often included on chip, as well as a small amount of RAM. Microcontrollers are designed for embedded applications, in contrast to the microprocessors used in personal computers or other general purpose applications consisting of various discrete chips.

<span class="mw-page-title-main">Embedded system</span> Computer system with a dedicated function

An embedded system is a computer system—a combination of a computer processor, computer memory, and input/output peripheral devices—that has a dedicated function within a larger mechanical or electronic system. It is embedded as part of a complete device often including electrical or electronic hardware and mechanical parts. Because an embedded system typically controls physical operations of the machine that it is embedded within, it often has real-time computing constraints. Embedded systems control many devices in common use. In 2009, it was estimated that ninety-eight percent of all microprocessors manufactured were used in embedded systems.

<span class="mw-page-title-main">AVR microcontrollers</span> Family of microcontrollers

AVR is a family of microcontrollers developed since 1996 by Atmel, acquired by Microchip Technology in 2016. These are modified Harvard architecture 8-bit RISC single-chip microcontrollers. AVR was one of the first microcontroller families to use on-chip flash memory for program storage, as opposed to one-time programmable ROM, EPROM, or EEPROM used by other microcontrollers at the time.

<span class="mw-page-title-main">Freescale 683XX</span>

The Freescale 683xx is a family of compatible microcontrollers by Freescale that use a Motorola 68000-based CPU core. The family was designed using a hardware description language, making the parts synthesizable, and amenable to improved fabrication processes, such as die shrinks.

<span class="mw-page-title-main">PIC microcontrollers</span> Line of single-chip microprocessors from Microchip Technology

PIC is a family of microcontrollers made by Microchip Technology, derived from the PIC1650 originally developed by General Instrument's Microelectronics Division. The name PIC initially referred to Peripheral Interface Controller, and is currently expanded as Programmable Intelligent Computer. The first parts of the family were available in 1976; by 2013 the company had shipped more than twelve billion individual parts, used in a wide variety of embedded systems.

In-circuit emulation (ICE) is the use of a hardware device or in-circuit emulator used to debug the software of an embedded system. It operates by using a processor with the additional ability to support debugging operations, as well as to carry out the main function of the system. Particularly for older systems, with limited processors, this usually involved replacing the processor temporarily with a hardware emulator: a more powerful although more expensive version. It was historically in the form of bond-out processor which has many internal signals brought out for the purpose of debugging. These signals provide information about the state of the processor.

Serial Peripheral Interface (SPI) is a de facto standard for synchronous serial communication, used primarily in embedded systems for short-distance wired communication between integrated circuits.

JTAG is an industry standard for verifying designs and testing printed circuit boards after manufacture.

Nios II is a 32-bit embedded processor architecture designed specifically for the Altera family of field-programmable gate array (FPGA) integrated circuits. Nios II incorporates many enhancements over the original Nios architecture, making it more suitable for a wider range of embedded computing applications, from digital signal processing (DSP) to system-control.

<span class="mw-page-title-main">In-system programming</span> Embedded system programming technique

In-system programming (ISP), or also called in-circuit serial programming (ICSP), is the ability of some programmable logic devices, microcontrollers, chipsets and other embedded devices to be programmed while installed in a complete system, rather than requiring the chip to be programmed prior to installing it into the system. It also allows firmware updates to be delivered to the on-chip memory of microcontrollers and related processors without requiring specialist programming circuitry on the circuit board, and simplifies design work.

ARM9 is a group of 32-bit RISC ARM processor cores licensed by ARM Holdings for microcontroller use. The ARM9 core family consists of ARM9TDMI, ARM940T, ARM9E-S, ARM966E-S, ARM920T, ARM922T, ARM946E-S, ARM9EJ-S, ARM926EJ-S, ARM968E-S, ARM996HS. Since ARM9 cores were released from 1998 to 2006, they are no longer recommended for new IC designs, instead ARM Cortex-A, ARM Cortex-M, ARM Cortex-R cores are preferred.

RS08 is a family of 8-bit microcontrollers by NXP Semiconductors. Originally released by Freescale in 2006, the RS08 architecture is a reduced-resource version of the Freescale MC68HCS08 central processing unit (CPU), a member of the 6800 microprocessor family. It has been implemented in several microcontroller devices for embedded systems.

<span class="mw-page-title-main">PICkit</span>

PICkit is a family of programmers for PIC microcontrollers made by Microchip Technology. They are used to program and debug microcontrollers, as well as program EEPROM. Some models also feature logic analyzers and serial communications (UART) tools.

The 9S08 is an 8-bit microcontroller (µC) family originally produced by Motorola, later by Freescale Semiconductor, and currently by NXP, descended from the Motorola 6800 microprocessor. It is a CISC microcontroller. A slightly extended variant of the 68HC08, it shares upward compatibility with the aging 68HC05 microcontrollers, and is found in almost any type of embedded systems. The larger members offer up to 128 KiB of flash, and 8 KiB of RAM via a simple memory management unit (MMU) which allows bank-switching 16 KiB of the address space and an address/data register pair which allows data fetches from any address. The paging scheme used allows for a theoretical maximum of 4 MB of flash.

Each time Intel launched a new microprocessor, they simultaneously provided a system development kit (SDK) allowing engineers, university students, and others to familiarise themselves with the new processor's concepts and features. The SDK single-board computers allowed the user to enter object code from a keyboard or upload it through a communication port, and then test run the code. The SDK boards provided a system monitor ROM to operate the keyboard and other interfaces. Kits varied in their specific features but generally offered optional memory and interface configurations, a serial terminal link, audio cassette storage, and EPROM program memory. Intel's Intellec development system could download code to the SDK boards.

A debug port is a diagnostic interface included in an electronic system or integrated circuit to aid design, fabrication, development, bootstrapping, configuration, debugging, and post-sale in-system programming. In general terms, a debug port is not necessary for end-use function and is often hidden or disabled in finished products.

Communications Processor Module (CPM) is a component of Motorola 68000 family (QUICC) or Motorola/Freescale Semiconductor PowerPC/Power ISA (PowerQUICC) microprocessors designed to provide features related to imaging and communications. A microprocessor can delegate most of the input/output processing to the Communications Processor Module and the microprocessor does not have to perform those functions itself. Some input/output functions require quick response from the processor, for example due to precise timing requirements during data transmission. With CPM performing those operations, the main microprocessor is free to perform other tasks.

<span class="mw-page-title-main">NXP LPC</span> Family of 32-bit microcontroller integrated circuits

LPC is a family of 32-bit microcontroller integrated circuits by NXP Semiconductors. The LPC chips are grouped into related series that are based around the same 32-bit ARM processor core, such as the Cortex-M4F, Cortex-M3, Cortex-M0+, or Cortex-M0. Internally, each microcontroller consists of the processor core, static RAM memory, flash memory, debugging interface, and various peripherals. The earliest LPC series were based on the Intel 8-bit 80C51 core. As of February 2011, NXP had shipped over one billion ARM processor-based chips.

The MSP432 is a mixed-signal microcontroller family from Texas Instruments. It is based on a 32-bit ARM Cortex-M4F CPU, and extends their 16-bit MSP430 line, with a larger address space for code and data, and faster integer and floating point calculation than the MSP430. Like the MSP430, it has a number of built-in peripheral devices, and is designed for low power requirements. In 2021, TI confirmed that the MSP432 has been discontinued and "there will be no new MSP432 products".

References

  1. "HCS08 Family Reference Manual". pp. 34–35. Retrieved February 6, 2024.