-D (disable auto‑erase) is unconditionally added to avrdude flags and breaks usbasp flash process

[sstefanov]

Summary

builder/main.py unconditionally appends -D to UPLOADERFLAGS for every AVR
upload, regardless of upload_protocol. This is correct for bootloader-based
uploads (Optiboot/stk500v1/v2) but silently corrupts flash when the upload
protocol is an ISP programmer (usbasp, usbtiny, arduino-as-isp,
stk500v2, avrispmkII, ...), because no chip‑erase happens and AVR flash
bits cannot transition from 0 back to 1 without an erase.

Location

builder/main.py:

env.Append(UPLOADERFLAGS=["-D"])

Reproduction

1. Configure any AVR env with upload_protocol = usbasp (or any ISP).
2. Flash firmware A.
3. Flash firmware B that has any 1 bit at a flash address where A had a 0.
4. avrdude reports verification error, first mismatch at byte 0x… with the
   read value showing extra zero bits.

Why it’s subtle

• Successful first‑time flashes (or flashes after a manual chip‑erase) work fine.
• Subsequent re‑flashes only fail at bytes whose new value introduces a 1
  where the old image had a 0. Failures appear random / intermittent and are
  often misattributed to USBasp signal noise.
• Skipping verify (-V) hides the corruption — code is actually wrong on the chip.

Proposed fix

Detect ISP-style upload protocols and omit -D (or add -e to force chip
erase) for them. Roughly:

ISP_PROTOCOLS = {"usbasp", "usbtiny", "stk500v2", "avrispmkII",
                 "arduino-as-isp", "atmelice_isp", "dragon_isp",
                 "jtag2isp", "jtag3isp", "pickit4_isp", "snap_isp"}

protocol = env.subst("$UPLOAD_PROTOCOL")
if protocol in ISP_PROTOCOLS:
    env.Append(UPLOADERFLAGS=["-e"])         # explicit chip erase
else:
    env.Append(UPLOADERFLAGS=["-D"])         # bootloader path

Environment

• platform-atmelavr: <version from pio platform show atmelavr>
• PlatformIO Core: <pio --version>
• avrdude: <avrdude -v first line>
• OS: <e.g. Linux>
• Programmer: USBasp clone, firmware bcdDevice 1.04
• Target: ATmega1284P (Sanguinololu/Anet A8 mainboard)