AVR Freaks

Ok, I had some time to mess around on my project and so far it is working perfectly.

I wrote a pure assembly program for Atmega88 setup to reset fuses on an ATiny.

For the 12 volt source, I used a Dickson style Charge Pump using only 3 diodes, 3 caps. (no transistor).

Built the charge pump to only require .1uf caps as these are easy to source (decoupling caps).

The pump driver uses 2 PWM pins set as anti-phase, with a frequency "tuned" to the .1uf caps.

I also control the charge pump source wit an IO pin, so the entire IO can go invisible to the target.

The end goal for this project is a "wedge" that goes between the AVRISP and the ATiny.

When the AVRISP tries to program a locked ATiny, my wedge quickly resets the fuse before Studio times out.

I have not tested my theory of a "man in the middle" attack as of yet, but assume it will work.

Some crude tests show that you can yank VCC off the target for a second and Studio will keep trying.

As long as my HV Resetter can get in there and do it's magic quickly, it should work fine.

After my Resetter does its thing, it completely releases all pins and goes invisible.

The end result... You can free up that reset pin on an ATiny and use only AVRStudio and an AVRisp.

Now the only part I am missing is a good document explaining the actual AVR HV Protocol.

I don't want to ONLY reset the fuses, as this leaves the internal 8MHz OSC set by default.

I want to change the fuses so they are set to : External OSC and no clock divide.

Does anyone know where I might find a DOC showing the full details of the AVR HV Protocol?

Also, if there is any interest in a pure assembly fuse resetter, I will post this project here.

Cheers!

Brad

I believe I have sorted it out.

When I wrote my ASM fuse resetter, I used some of the other examples to get the Data,Instuction sequence.

I just figured this sequence told the ATTiny to go back to factory defaults.

From what I am being told, these are the actual fuse settings, so I just need to find the DOC file to explain them all.

To further explain what weirdness I am doing here...

I have an ATTiny project that requires every single IO pin and every last byte of program memory.

Obviously, gaining back PINB.5 requires setting the fuses to disable reset, which also disables the ability to program the part using AVRStudio and an AVRisp.

To get around this, some have made simple "Fuse Resetter" program that require pulling the ATTiny, putting it on another breadboard, running a reset program, then putting it back on the original breadboard with the fuses set to the default internal 8MHz osc with clock divide enabled.

To me, this limitation and lengthy kludge is not acceptable.

What I did is study a few of these resetters, and rewrote one in pure assembly that works as fast as possible. I also took inspiration from Wayne Holder's excellent resetter project shown here that uses a Dickson Charge Pump to generate the 12 volts required for HVSP...

https://sites.google.com/site/wa...

I simplified the Charge Pump idea down to only 3 diodes, and 3 decoupling caps (.1uf), and it does not require a transistor.

I also wrote my resetter to tristate all pins so that it can become "invisible" to the target.

My final evil plan is to have my resetter perform a "Main in The Middle" attack on my AVRISP so that it will hijack the programming bus just as Studio initiates an ISP to the AVRISP. Becasue the AVRISP does take a few seconds to realize that the ATTiny is locked, I believe that within this time, I can quickly set the fuses back to the desired settings, which for this project would be...

RSTDISBL : Disabled
SPIEN : Enabled
CKDIV8 : Disabled
SUT_CKSEL = EXCLK_6CK_14CK_0MS

Once the resetter quickly intervenes and sets the fuses, it then hides by tristating all of its pins, and hopefully, ARStudio will be able to complete a normal programming.

This way, I am able to free the ATTiny pin without jumping through hoops like a Circus Monkey each time I want to program the chip.

Since I run a programming sequence several hundred times during an afternoon, this would be painful indeed!

So now I just need to dig up the codes for the fuse settings I want.

When I have access to a real internet again, i will try downloading the "big" datasheet.

Cheers,

Brad

Ok, thanks for the highlighting! The info was all there, but it was my lack of experienc with fuse bits that made it invisible. I have what I need now.

Yes, I do in fact "code and burn" often more than once per minute.

When you are writing VGA demos that require line by line line chasing, your debugger is your monitor!

Often, one single instruction is enough to make it or break it, so I hit "program" a LOT!

This new approach to HV programming is a continuation of this project...

https://www.avrfreaks.net/forum/a...

Which was created to support this project...

https://www.avrfreaks.net/comment...

The "Self Replicating Boot Unloader" did work, but it had some drawbacks.

First, it ate 1K of program memory, which is too much on an ATTiny.

Second, it could brick the ATTiny if you did something really stupid, and this would require an HV resetter.

So now, I have solved every annoyance and gotcha associated with the ATTiny series...

- You can now use every IO pin properly.

- You get to use 100% of the program memory.

- You can work with Studio and an AVRISP only.

I enjoyed the Quark-85 VGA Demo System so much that I want to keep it going.

After my brief  seduction to to PIC8 and PIC32, I truly appreciate how unmatched the AVR is.

Anyhow, thanks again for the pointers (and I ain't talkin' no C lingo when I say that!).

I will post this simple project here with code and photos when I get it completed.

One last question if I may!...

I heard that it is possible to add the fuse settings in code, and found this C example...

FUSES =
{
.low = LFUSE_DEFAULT,
.high = (FUSE_BOOTSZ0 & FUSE_BOOTSZ1 & FUSE_EESAVE & FUSE_SPIEN & FUSE_JTAGEN),
.extended = EFUSE_DEFAULT,
};

I am not sure if the above does anything, as I am an assembly dude, so if anyone knows if it is possible to define fuse settings in code (without screwing around with make files and such), this would be nice to know.

My program is a single main.s file (GCC GAS) program.

Cheers,

Brad

Just wanted to say thanks again, I now have the fuses being written as required.

The final step will be to isolate the project onto a board that plugs between AVRISP and Breadboard.

Hey Joey, how did you implement your Charge Pump?

This is how I did mine...

Dual IO Pins set for PWM at 500KHz, each at 180 degrees to the other.

At this frequency, I found that .1uf caps were ideal to generate the ~12 volts.

Taking into consideration the internal resistance of the reset pin, I have 4 caps and 3 diodes.

3 caps and 3 diodes form the pump, and the 4th cap is the "buffer" to smooth the pulsed DC.

To control the HV, I disable PWM and set the Charge Pump input pin to Low.

To make this thing "part of" my AVRISP, I now actually power the ATTiny directly from the ATMega99 IO pins!

Several IO pins are tied together to source VCC to the ATTiny, although I found one IO to be fine.

The last piece of the puzzle is going to be the switching of the ATTiny external oscillator module.

It has no EN pin, so I will need to route it to the Resetter board and back, through an HC logic switch.

Once completed, the Resetter will be invisible to be toolchain, which consists of only Studio7 and an AVRISP.

Now I can utilize 100% of the ATTiny resources (or lack thereof)... 6 IO pins, and all of the Program Memory.

.... All this just to push the ATTiny a little further! Already running it at 36MHz!

Cheers!

Brad

The Homestead has been keeping me extremely busy, but I did get a few hours to finish my new programmer, and it works great!

I now have what may be the first "AVRISP compatible In Circuit ATiny HV Programmer" ever!

Well, it really isn't a programmer, it just does a quick fuse programming through HVSP right before Studio takes control with the AVRISP.

To make this work, I actually ended up using 2 DPDT relays salvaged from old modems.

The relays disconnect the external oscilator, VCC, and a few other pins to allow the HV programmer to "Hijack" the ATiny for a few milliseconds.

Now I can program in AVRStudio using my AVRISP, and can use every IO pin on the ATiny, even the normally unavailable PINB.5 (reset).

The only thing I have not been able to do is specify the fuse settings in my code (see my question in post #16).

I need to set the RSTDISBL fuse to disabled so I don't have to open the fuse dialog each time, which adds an extra step.

It seems you can do this in C or with something called an AVR Dude, but I use neither.

Does anyone know if this can be done in a Studio6.2 Assembly program?

Some kind of #define or assembler switch?

Have not found anything in my searching yet.

Cheers!

Brad