Problem with bootloader and uploading sketch to custom "Arduino" pcb

[cocopa]

Hello everyone, I know that there are a lot of similar posts but I couldn't find an answer..

I designed my own custom pcb as Arduino-Uno equivalent and I'm trying to program it.
First, I tried to burn the bootloader to ATMEga328P using an arduino mega 2560 as programmer, as suggested in the documentation but I get either "Invalid device signature error" or "Expected signature for ATmega328P is 1E 95 0F" avrude error. I managed to burn the bootloader using this code and everything completes successfully (including verification).

After that, I programmed ATMEGA16U2 using Flip 3.4.7 software to upload the hex file found here and finally the board is recognized as Arduino Uno.

It is displayed correctly under device manager, in Arduino IDE (v.1.8.19) it is also shown correctly in the appropriate port and I can also get back the board info (BN, VID, PID, SN).
However, when I try to upload a sketch through the IDE I get the following error:

An error occurred while uploading the sketch avrdude: stk500_recv(): programmer is not responding avrdude: stk500_getsync() attempt 1 of 10: not in sync: resp=0xc2

I've checked polarity of tx/rx lines, DTR signal is connected correctly and I can't figure out what might be going wrong. Any help would be much appreciated.

[sterretje]

I suspect that those in the know (I'm not one of them) might want to see your schematic.

[cocopa]

Yes, I attach the part of the schematic related to the "Arduino core".

[cocopa]

One more update from my side, if it helps.
I used again code from Nick Gammon's forum to readback the contents of the chip that I want to program and I got the response below, which I believe looks normal.
One thing that I noticed, is that the chip type is ATMega328 and not ATMega328P, could this create a problem? The code for ATMega16U2 targeting Arduino Uno is expecting ATMega328P, is it possible that they have different signatures and something is going wrong there?
Thanks again.

Atmega chip detector.
Written by Nick Gammon.
Version 1.20
Compiled on Jun 7 2022 at 20:24:30 with Arduino IDE 10609.
Attempting to enter ICSP programming mode ...
Entered programming mode OK.
Signature = 0x1E 0x95 0x14
Processor = ATmega328
Flash memory size = 32768 bytes.
LFuse = 0xFF
HFuse = 0xDE
EFuse = 0xFD
Lock byte = 0xEF
Clock calibration = 0x46
Bootloader in use: Yes
EEPROM preserved through erase: No
Watchdog timer always on: No
Bootloader is 512 bytes starting at 7E00

Bootloader:

7E00: 0x11 0x24 0x84 0xB7 0x14 0xBE 0x81 0xFF 0xF0 0xD0 0x85 0xE0 0x80 0x93 0x81 0x00
7E10: 0x82 0xE0 0x80 0x93 0xC0 0x00 0x88 0xE1 0x80 0x93 0xC1 0x00 0x86 0xE0 0x80 0x93
7E20: 0xC2 0x00 0x80 0xE1 0x80 0x93 0xC4 0x00 0x8E 0xE0 0xC9 0xD0 0x25 0x9A 0x86 0xE0
7E30: 0x20 0xE3 0x3C 0xEF 0x91 0xE0 0x30 0x93 0x85 0x00 0x20 0x93 0x84 0x00 0x96 0xBB
7E40: 0xB0 0x9B 0xFE 0xCF 0x1D 0x9A 0xA8 0x95 0x81 0x50 0xA9 0xF7 0xCC 0x24 0xDD 0x24
7E50: 0x88 0x24 0x83 0x94 0xB5 0xE0 0xAB 0x2E 0xA1 0xE1 0x9A 0x2E 0xF3 0xE0 0xBF 0x2E
7E60: 0xA2 0xD0 0x81 0x34 0x61 0xF4 0x9F 0xD0 0x08 0x2F 0xAF 0xD0 0x02 0x38 0x11 0xF0
7E70: 0x01 0x38 0x11 0xF4 0x84 0xE0 0x01 0xC0 0x83 0xE0 0x8D 0xD0 0x89 0xC0 0x82 0x34
7E80: 0x11 0xF4 0x84 0xE1 0x03 0xC0 0x85 0x34 0x19 0xF4 0x85 0xE0 0xA6 0xD0 0x80 0xC0
7E90: 0x85 0x35 0x79 0xF4 0x88 0xD0 0xE8 0x2E 0xFF 0x24 0x85 0xD0 0x08 0x2F 0x10 0xE0
7EA0: 0x10 0x2F 0x00 0x27 0x0E 0x29 0x1F 0x29 0x00 0x0F 0x11 0x1F 0x8E 0xD0 0x68 0x01
7EB0: 0x6F 0xC0 0x86 0x35 0x21 0xF4 0x84 0xE0 0x90 0xD0 0x80 0xE0 0xDE 0xCF 0x84 0x36
7EC0: 0x09 0xF0 0x40 0xC0 0x70 0xD0 0x6F 0xD0 0x08 0x2F 0x6D 0xD0 0x80 0xE0 0xC8 0x16
7ED0: 0x80 0xE7 0xD8 0x06 0x18 0xF4 0xF6 0x01 0xB7 0xBE 0xE8 0x95 0xC0 0xE0 0xD1 0xE0
7EE0: 0x62 0xD0 0x89 0x93 0x0C 0x17 0xE1 0xF7 0xF0 0xE0 0xCF 0x16 0xF0 0xE7 0xDF 0x06
7EF0: 0x18 0xF0 0xF6 0x01 0xB7 0xBE 0xE8 0x95 0x68 0xD0 0x07 0xB6 0x00 0xFC 0xFD 0xCF
7F00: 0xA6 0x01 0xA0 0xE0 0xB1 0xE0 0x2C 0x91 0x30 0xE0 0x11 0x96 0x8C 0x91 0x11 0x97
7F10: 0x90 0xE0 0x98 0x2F 0x88 0x27 0x82 0x2B 0x93 0x2B 0x12 0x96 0xFA 0x01 0x0C 0x01
7F20: 0x87 0xBE 0xE8 0x95 0x11 0x24 0x4E 0x5F 0x5F 0x4F 0xF1 0xE0 0xA0 0x38 0xBF 0x07
7F30: 0x51 0xF7 0xF6 0x01 0xA7 0xBE 0xE8 0x95 0x07 0xB6 0x00 0xFC 0xFD 0xCF 0x97 0xBE
7F40: 0xE8 0x95 0x26 0xC0 0x84 0x37 0xB1 0xF4 0x2E 0xD0 0x2D 0xD0 0xF8 0x2E 0x2B 0xD0
7F50: 0x3C 0xD0 0xF6 0x01 0xEF 0x2C 0x8F 0x01 0x0F 0x5F 0x1F 0x4F 0x84 0x91 0x1B 0xD0
7F60: 0xEA 0x94 0xF8 0x01 0xC1 0xF7 0x08 0x94 0xC1 0x1C 0xD1 0x1C 0xFA 0x94 0xCF 0x0C
7F70: 0xD1 0x1C 0x0E 0xC0 0x85 0x37 0x39 0xF4 0x28 0xD0 0x8E 0xE1 0x0C 0xD0 0x85 0xE9
7F80: 0x0A 0xD0 0x8F 0xE0 0x7A 0xCF 0x81 0x35 0x11 0xF4 0x88 0xE0 0x18 0xD0 0x1D 0xD0
7F90: 0x80 0xE1 0x01 0xD0 0x65 0xCF 0x98 0x2F 0x80 0x91 0xC0 0x00 0x85 0xFF 0xFC 0xCF
7FA0: 0x90 0x93 0xC6 0x00 0x08 0x95 0x80 0x91 0xC0 0x00 0x87 0xFF 0xFC 0xCF 0x80 0x91
7FB0: 0xC0 0x00 0x84 0xFD 0x01 0xC0 0xA8 0x95 0x80 0x91 0xC6 0x00 0x08 0x95 0xE0 0xE6
7FC0: 0xF0 0xE0 0x98 0xE1 0x90 0x83 0x80 0x83 0x08 0x95 0xED 0xDF 0x80 0x32 0x19 0xF0
7FD0: 0x88 0xE0 0xF5 0xDF 0xFF 0xCF 0x84 0xE1 0xDE 0xCF 0x1F 0x93 0x18 0x2F 0xE3 0xDF
7FE0: 0x11 0x50 0xE9 0xF7 0xF2 0xDF 0x1F 0x91 0x08 0x95 0x80 0xE0 0xE8 0xDF 0xEE 0x27
7FF0: 0xFF 0x27 0x09 0x94 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0x04 0x04

MD5 sum of bootloader = 0xFB 0xF4 0x9B 0x7B 0x59 0x73 0x7F 0x65 0xE8 0xD0 0xF8 0xA5 0x08 0x12 0xE7 0x9F
Bootloader name: optiboot_atmega328

First 256 bytes of program memory:

00: 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF
10: 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF
20: 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF
30: 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF
40: 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF
50: 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF
60: 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF
70: 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF
80: 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF
90: 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF
A0: 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF
B0: 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF
C0: 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF
D0: 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF
E0: 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF
F0: 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF

Programming mode off.

[westfw]

You have a 1k resistor on the 328 RESET signal, and it should probably be 10k.
(some Nanos have 1k pullups, but they don't have the 1k pulldown on DTR. (And they're wrong.))

The 328 vs 328p may be a thing as well, but you would get an "invalid signature" error rather than "not repsonding." (maybe not, depending on whether the bootloader is the lying version or not.)

[cocopa]

Hi westfw, thanks for your answer. Actually I have already changed the resistor and the 1uF cap (which is now 100nF) on the DTR signal.
The 328 vs 328P issue I think that explains at least why I couldn't burn the bootloader with the standard way through Arduino IDE and I was getting the invalid signature error.