getchar() / putchar() (Part 2)

• We’ll add a 1-character buffer for both input and output

• getchar()

  • interrupt when a new character arrives
  • if the buffer is empty, place character in buffer
  • otherwise, set error flag (new function to check for errors)
  • getchar() now looks at the buffer for a character
  • otherwise the same as before

• putchar()

  • interrupt when a character has been sent
  • if the buffer has a character, send it to the serial port
  • putchar() now puts the character into the buffer
  • otherwise the same as before
  • what if the buffer is empty when interrupt occurs?
    • new character to buffer will not be sent

• Complication: one interrupt routine for both input and output

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