The ATtiny85 has no hardware TWI; TinyWireM/Tiny4kOLED drive I2C through the USI
peripheral (SDA=PB0, SCL=PB2). avr8js ships AVRUSI but velxio never instantiated
it, so the I2C bus had no master on the ATtiny85 and devices (e.g. SSD1306 OLED)
got no data — the display stayed blank (and wokwi-ssd1306 threw putImageData with
an empty framebuffer). New UsiI2cBridge instantiates AVRUSI and sniffs the SDA/SCL
lines, replaying START/STOP + 8-bit bytes onto the shared I2C bus as
start/connectToSlave/writeByte/stop (the same calls AVRTWI makes for the Uno).
Validated against real ATTinyCore Tiny4kOLED firmware: decodes addr 0x3C + SSD1306
init/data stream. Firmware tolerates NACK so the sniffer is passive.
David Montero