+ /* extra_key is volatile and more convoluted than necessary because gcc refused
+ to generate valid code otherwise. Making extra_key uint8_t and constructing codes
+ here via codes = extra_key<<8 | 0xFF; would consistently fail to even LOAD
+ extra_key from memory, and leave garbage in the high byte of codes. I tried
+ dozens of code variations and it kept generating broken assembly output. So
+ beware if attempting to make extra_key code more logical and efficient. */
+ static volatile uint16_t extra_key = 0xFFFF;