Reliably programming Atmel AVR µCs at 3.3v using USBasp

Development Tools Uploading
1

I am building a few devices based on some AVR µCs (4 ATtiny84s and a single ATmega328P). I will have a few modules attached which need to run at 3.3v (nRF24L01 transceivers and a ST7735 LCD) and I'd really like to do in-circuit serial programming so I don't need to remove the µC from its socket or have to disconnect the modules every time I compile and upload the code. The PCB which I have designed but not yet sent for manufacturing has a provision for a standard 6-pin ICSP header and it would be great if I could make use of it.

I have three USBasp programmers and all of them always upload the sketch flawlessly at 5v but as soon as I switch the jumper to 3.3v it fails randomly, sometimes many times in a row and other times rarely. I also have the impression that one of the USBasp programmers fails more often than the others but it may be a coincidence. When the upload fails, the LED which is supposed to blink does not turn on at all. Once it's successful again (which can be forced by using 5v or happens on its own after multipe retries), the LED blinks as expected.

I've tried a decoupling capacitor between Vcc and GND and a pull-up resistor on the reset pin to no avail. I made sure the firmware on all three is up to date and I've tried using a different ATtiny chip and an ATmega and the problem persists.

Below is the very basic code I'm testing with and the output from the Arduino IDE (in this case I have an ATtiny85 connected):

void setup() {
  pinMode(3, OUTPUT);
}

void loop() {
  digitalWrite(3, HIGH);
  delay(1000);
  digitalWrite(3, LOW);
  delay(1000);
}

Sketch uses 458 bytes (5%) of program storage space. Maximum is 8192 bytes.
Global variables use 9 bytes (1%) of dynamic memory, leaving 503 bytes for local variables. Maximum is 512 bytes.
"C:\Users\neu\AppData\Local\Arduino15\packages\arduino\tools\avrdude\6.3.0-arduino18/bin/avrdude" "-CC:\Users\neu\AppData\Local\Arduino15\packages\ATTinyCore\hardware\avr\1.5.2/avrdude.conf" -v -pattiny85 -cusbasp  "-Uflash:w:C:\Users\neu\AppData\Local\Temp\arduino\sketches\489E94CF512C274DFBBBE22A8474D1CE/Blink.ino.hex:i"

avrdude: Version 6.3-20201216
         Copyright (c) 2000-2005 Brian Dean, http://www.bdmicro.com/
         Copyright (c) 2007-2014 Joerg Wunsch

         System wide configuration file is "C:\Users\neu\AppData\Local\Arduino15\packages\ATTinyCore\hardware\avr\1.5.2/avrdude.conf"

         Using Port                    : usb
         Using Programmer              : usbasp
         Setting bit clk period        : 5.0
         AVR Part                      : ATtiny85
         Chip Erase delay              : 400000 us
         PAGEL                         : P00
         BS2                           : P00
         RESET disposition             : possible i/o
         RETRY pulse                   : SCK
         serial program mode           : yes
         parallel program mode         : yes
         Timeout                       : 200
         StabDelay                     : 100
         CmdexeDelay                   : 25
         SyncLoops                     : 32
         ByteDelay                     : 0
         PollIndex                     : 3
         PollValue                     : 0x53
         Memory Detail                 :

                                  Block Poll               Page                       Polled
           Memory Type Mode Delay Size  Indx Paged  Size   Size #Pages MinW  MaxW   ReadBack
           ----------- ---- ----- ----- ---- ------ ------ ---- ------ ----- ----- ---------
           eeprom        65    12     4    0 no        512    4      0  4000  4500 0xff 0xff
           flash         65    12    32    0 yes      8192   64    128 30000 30000 0xff 0xff
           signature      0     0     0    0 no          3    0      0     0     0 0x00 0x00
           lock           0     0     0    0 no          1    0      0  9000  9000 0x00 0x00
           lfuse          0     0     0    0 no          1    0      0  9000  9000 0x00 0x00
           hfuse          0     0     0    0 no          1    0      0  9000  9000 0x00 0x00
           efuse          0     0     0    0 no          1    0      0  9000  9000 0x00 0x00
           calibration    0     0     0    0 no          2    0      0     0     0 0x00 0x00

         Programmer Type : usbasp
         Description     : USBasp, http://www.fischl.de/usbasp/

avrdude: set SCK frequency to 187500 Hz
avrdude: AVR device initialized and ready to accept instructions

Reading | ################################################## | 100% 0.00s

avrdude: Device signature = 0x1e930b (probably t85)
avrdude: NOTE: "flash" memory has been specified, an erase cycle will be performed
         To disable this feature, specify the -D option.
avrdude: erasing chip
avrdude: set SCK frequency to 187500 Hz
avrdude: reading input file "C:\Users\neu\AppData\Local\Temp\arduino\sketches\489E94CF512C274DFBBBE22A8474D1CE/Blink.ino.hex"
avrdude: writing flash (458 bytes):

Writing | ################################################## | 100% 0.33s

avrdude: 458 bytes of flash written
avrdude: verifying flash memory against C:\Users\neu\AppData\Local\Temp\arduino\sketches\489E94CF512C274DFBBBE22A8474D1CE/Blink.ino.hex:
avrdude: load data flash data from input file C:\Users\neu\AppData\Local\Temp\arduino\sketches\489E94CF512C274DFBBBE22A8474D1CE/Blink.ino.hex:
avrdude: input file C:\Users\neu\AppData\Local\Temp\arduino\sketches\489E94CF512C274DFBBBE22A8474D1CE/Blink.ino.hex contains 458 bytes
avrdude: reading on-chip flash data:

Reading | ################################################## | 100% 0.15s

avrdude: verifying ...
avrdude: verification error, first mismatch at byte 0x0000
         0x00 != 0x0e
avrdude: verification error; content mismatch

avrdude done.  Thank you.

Failed programming: uploading error: exit status 1

How can I solve this? Thanks!

2

Use a Polou;

https://www.pololu.com/docs/0J67

Yes the other USBasp programmers should work, in an ideal World, and if the PCB design is good, but the Pololu just works.

You may have to slow the Pololua right down (easy) but thats not a real issue for uploading programs or bootloaders.

What has the Sketch your trying to upload have to do with the problems you are having ?

3

Thanks for your suggestion. Are there any solutions using the existing USBasp and without buying more hardware? If not, I found a Pololu for 13,10 € in my region and I'm considering buying it if I need to.

I just included it in case someone wanted to see it.

4

If your modules (e.g. the screen) use the SPI bus, it might interfere with the ICSP upload process.

5

I'm not convinced that's it. Right now I have no modules attached and the code is as barebones as possible. Still it doesn't work well on 3.3v but it does on 5v.

I also tried attaching the ST7735 LCD with 5v logic with a simple voltage divider for the 3.3v backlight as a test and it works reliably.

6

I received the Pololu programmer and tried it out and it seems to work the way I want.

7

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