Atmel makes several Debuggers for the ATMega328P chips:
AVR Dragon, $49
The AVR Dragon sets a new standard for low cost development tools for 8-bit and 32-bit AVR devices with On Chip Debug (OCD) capability. It can perform a symbolic debug on all devices with OCD with SPI, JTAG, PDI (selected devices), high voltage serial programming, parallel programming, and aWire modes, and supports debugging using SPI, JTAG, PDI interfaces.
A development area lets designers build their own circuitry or add sockets for the desired device footprint. The debugger also supports NanoTrace, depending on the OCD module on the AVR devic, using the target device's memory.
Key Features•Supports up to 3 hardware program breakpoints or 1 maskable data breakpoint (depending on the OCD mo
•Supports up to 32 software breakpoints
•On-board 128kB SRAM for fast statement-level stepping
•Robust level converters support 1.8V to 5.5V target operation
•Uploads 256Kb code in ~60 seconds (XMEGA using JTAG interface)
•Full-speed USB 2.0 compliant host interface (12 MB/s)
•Firmware upgradeable for supporting future AVR devices
•Supports NanoTrace (depending on the OCD module on the AVR device; uses target device's memory)
•USB powered, and capable of sourcing power to an external target
AVR JTAGICE mkII, $299
A mid-range development tool for Atmel 8-bit and 32-bit AVR devices with on-chip debugging for source level symbolic debugging, NanoTrace (if supported by the device) and device programming. It supports SP, JTAG, PDI, and aWire modes and interface debugging. The tool is firmware upgradeable to support future AVR devices.
Key Features•Supports up to 3 hardware program breakpoints or 1 maskable data breakpoint (depending on the OCD mo
•Supports symbolic debug of complex data types including scope information
•Supports up to 128 software breakpoints
•Includeson-board 512kB SRAM for fast statement-level stepping
•Level converters support 1.8V to 5.5V target operation
•Uploads 256Kb code in ~30 seconds (XMEGA using JTAG interface)
•Full-speed USB 2.0 compliant (12 MB/s) and RS-232 host interfaces
•Externally or USB powered
A professional development tool for all Atmel 8-bit and 32-bit AVR devices with On-Chip Debug capability. It is used for source level symbolic debugging, program trace and device programming. AVR ONE! supports the complete development cycle and is is the fastest debugging tool offered from Atmel.
AVR ONE!, $599
It supports SPI, JTAG, PDI, and aWire programming modes and debugging using debugWIRE, JTAG, PDI, and aWire interfaces. It also supports LiveDebug, which makes it possible to attach to a running target non-intrusively, and the Nexus auxiliary interface for high-speed program, data or ownership trace at up to 200MHz in either buffered or streaming mode. AVR ONE! is driven by powerful FPGA which provides high-speed data transfer between the host PC and the target AVR device, facilitating rapid program download and a most responsive debugging experience.
Key Features•Supports up to 3 hardware program breakpoints or 1 maskable data breakpoint (depending on the OCD mo
•Supports symbolic debug of all datatypes including scope information
•Supports up to 128 software breakpoints
•Includes on-board 128kB SRAM for fast statement-level stepping
•Robust level converters support 1.8V to 5.5V target operation
•AUX trace supports up to 3.3V. A 5.5V tolerant trace probe is available
•Uploads 256Kb code in ~8 seconds (XMEGA using JTAG interface)
•High-speed USB 2.0 compliant host interface (480 MB/s) for easy handling of trace data
•Fully adjustable high-resolution clock up to 64MHz
•Supports LiveDebug (OCD specific)
•Firmware upgradeable for supporting future AVR devices
•128MB SDRAM for AUX trace data buffering in linear or circular modes
•Supports NanoTrace (depending on the OCD module on the AVR device; uses target device's memory)
JTAGICE 3, $199
Mid-range development tool for Atmel 8-bit and 32-bit AVR microcontrollers with on-chip debugging for source level symbolic debugging, NanoTrace (if supported by the device) and device programming.
Key Features•Supports JTAG, aWire, SPI and PDI interfaces
•3 hardware program breakpoints and 1 maskable data breakpoint (depending on the OCD module on the AV
•Symbolic debug of complex data types including scope information
•Up to 128 software breakpoints
•1.8V to 5.5V target operation
•Uploads 256KB code in ~14 seconds (XMEGA using JTAG interface)
•USB powered
Can do a lot with serial.print, serial.write statements too.