Update:
I tried removing the printer and tried to read Bluetooth data (without printing) and it worked fine. Tried reading about 200000 bytes with 2000 bytes every single time with a delay of a sec or two max and it worked well and at good speed.
When I connect printer and read the data and as well print, I am able to read the data for few KB (This is random) and then the data read/reception is delayed... Say for few seconds and then I get next byte... again prints properly for few hundred bytes and again hangs or say delay in data reception.
I would have activated strobes while I am printing and at the same time the bluetooth data is read in circular buffer (via UART receiver interrupt).
Is excess current drawn causing this issue. I see the voltage drop at the battery.
Some boards work perfectly fine but max dont.
I tried 4 strobes (Max current), 2 and even 1 strobe (low current) drive to check if it excess current drawn but couldnt get a clue.
Strobe current depends on what I am printing hence donot know exact current. Datasheet says if all dots of one strobe in ON it takes about 2.4 amps.
Could this be ESD?
Could this be current?
Is my regulator voltage (3.3V) varying... Seems stable when checked on CRO
Could that be some noise??
I am just not sure which way to go from here
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Correction:
PCBs from old fab also have issue but the issue arises after some 50-70 prints while with new fab, it after 5-10 prints
Its not the MCU buffer that is the issue (debugged it and found that the bluetooth isnt receiving (I m not sure if its stored in bluetooth module buffer) data at all)