This page is taken from TODO file in source root. Some points are maybe obsolete or done. This have to be checked!


  • Running simulavr as part of the WinAVR tool chain.

  • Export additional hardware (LCDs etc.) to verilog

  • State saving support: Saving/restoring the complete state of the simulation (this needs a lot of infrastructure) Is this needed?

  • Waiting at a breakpoint for a GDB user input: the active wait-loop should be replaced by something using less CPU power. (maybe solved?)

Host specific issues

  • In the moment no support on Windows and Mac OS. Question is: is this maybe obsolete by using docker?

Feature parity with avrtest

Known issues:

  • Verify gcc test suite can be run with avrtest (maybe solved?)

Feature parity with old simulavr

Known issues:

  • avr-libc mostly tests with AT90S8515 and ATmega128 so most is OK

  • Models not yet supported (this is a historical list, many modern models are also not supported!):

    • AT90S2313 -

    • AT90S4414 - essentially AT90S8515 w/less memory so easy

    • AT90S1200 - different, can be ignored as obsolete

    • ATmega103 - can be ignored as obsolete

    • range of AT43USBxxx controllers - can be ignored as replaced (sorta) by the AT90USB* / ATmega???U? devices.

Configure issues

Should be ok with cmake scripts. If not, please help us with a comment on bug list!

Known limitations of current CPU models

  • TWI Serial Interface missing

  • Analog to Digital Converter Subsystem need to be validated

  • Boot Loader Support (fuses, different reset vector, switching interrupt vector table, …) not supported

  • Real Time Clock missing

  • Watchdog Timer status unclear

  • Sleep-command not working

  • Reset-pin is not available. Also different reset reasons are not supported

  • With activating the Tx-Pin of an UART the DDR-Register is not set properly to output. Workaround: Set the Pin’s default value to PULLUP. While the Pin behaves as Open Colletor (pulls down only) the pull-up “resistor” lets the system run as it should.

  • There are always 64kByte of external memory automatically attached to the Mega128. Different memory sizes are not supported.

  • Segments different than .text, .data, .bss are not supported

Known limitation of other/new CPU models

  • While Atmel changed some function details of the EEPROM, Watchdog Timer, Timer Subsystem, ADC, and USART / USI these subsystems have identical names but different functions. Therefore adding a new CPU needs a detailed analysis of the functions of each IO-subsystem

  • CPUs with 24bit program counter are not supported

  • CAN-subsystem is missing

  • USB subsystem is missing

  • X-Mega specifics are missing

Known issues of the TCL simulator part

  • LCD subsystem is simlified to

    • only a 4*20 character type is available

    • the timing is fixed as described for the 5V-versions

    • only the 4 bit interface is supported. At start-up the commands are interpreted as if an eight bit interface is available (one write cycle per command). After finishing the initialization switching to the four bit interface is permitted at any time.

    • the graphic representation is character based. Display of of characters

      follows the rules of your display, not of the LCD character generator.

    • loadable characters are not supported.

    • reading of display is not supported.

    • reading of busy flag does not give the current address in the lower bits.

    • scrolling not supported.

    • shift right / left of the display content is not supported.

    • only one character set is supported - based on your diplay font.

  • Scope subsystem is an empty frame

  • Serial Rx/Tx is simplfied to

    • only 8 bit data transmission is supported

    • 9 bit handling (MPM) is not supported


  • All tests need to be integrated into a nice regression test suite (Maybe python unittest?), this is made for some tests, not for all. Right now, the tests are split up and there is a custom made regression test suite for testing the handling of instructions in the core.


  • Make the device names configurable and not only a simple index into a list. Do not update bxxxx values in trace output.

  • Implement PCb back.

  • Bug, nothing in SREG? Why SREG twice?

  • Have an optional constraint on the number of bits in trace_direct (to e.g. only trace the necessary stack bits).