Data exchange using fan unit signal lines

1. A fan unit comprising:

a fan;

a pulse width modulated (PWM) signal line;

a tachometric signal line; and

a fan unit controller configured to:

receiving a PWM signal on the PWM signal line;

detecting that a frequency of the PWM signal is outside a frequency range used to control a fan speed of the fan;

selecting a data output based on the frequency of the PWM signal; and

sending the data output on the tachometric signal line.

2. The fan unit of claim 1 , wherein the data output comprises an identifier of the fan unit.

3. The fan unit of claim 1 , wherein selecting the data output based on the frequency of the PWM signal comprises dynamically generating the data output based on a characteristic of the fan unit.

4. The fan unit of claim 1 , wherein selecting the data output based on the frequency of the PWM signal comprises selecting the data output describing an error associated with the fan unit.

5. The fan unit of claim 1 , wherein detecting that the frequency of the PWM signal is outside the frequency range used to control the fan speed of the fan comprises maintaining a current fan speed until a subsequent PWM signal is received on the PWM signal line.

6. The fan unit of claim 1 , wherein sending the data output on the tachometric signal line comprises interrupting tachometric pulses indicating the fan speed on the tachometric signal line.

7. The fan unit of claim 1 , wherein detecting that the frequency of the PWM signal is outside the frequency range used to control the fan speed of the fan comprises extracting a parameter from the PWM signal.

8. The fan unit of claim 7 , wherein selecting the data output based on the frequency of the PWM signal comprises:

adjusting a setting of the fan unit based on the parameter from the PWM signal; and

selecting, as the data output, an acknowledgement that the parameter is has been set.

9. The fan unit of claim 1 , wherein the PWM signal line and the tachometric signal line are communicatively coupled to a baseboard management controller.

10. A computer program product including a computer readable medium, the computer program product comprising computer program instructions that, when executed, cause a computer to carry out the steps of:

receiving a pulse width modulated (PWM) signal on a PWM signal line of a fan unit;

detecting that a frequency of the PWM signal is outside a frequency range used to control a fan speed of a fan in the fan unit;

selecting a data output based on the frequency of the PWM signal; and

sending the data output on a tachometric signal line of the fan unit.

11. The computer program product of claim 10 , wherein the data output comprises an identifier of the fan unit.

12. The computer program product of claim 10 , wherein selecting the data output based on the frequency of the PWM signal comprises dynamically generating the data output based on a characteristic of the fan unit.

13. The computer program product of claim 10 , wherein selecting the data output based on the frequency of the PWM signal comprises selecting the data output describing an error associated with the fan unit.

14. The computer program product of claim 10 , wherein detecting that the frequency of the PWM signal is outside the frequency range used to control the fan speed of the fan comprises maintaining a current fan speed until a subsequent PWM signal is received on the PWM signal line.

15. The computer program product of claim 10 , wherein sending the data output on the tachometric signal line comprises interrupting tachometric pulses indicating the fan speed on the tachometric signal line.

16. The computer program product of claim 15 , wherein the fan information is an identifier of the fan unit.

17. The computer program product of claim 10 , wherein detecting that the frequency of the PWM signal is outside the frequency range used to control the fan speed of the fan comprises extracting a parameter from the PWM signal.

18. The computer program product of claim 17 , wherein selecting the data output based on the frequency of the PWM signal comprises:

adjusting a setting of the fan unit based on the parameter from the PWM signal; and

selecting, as the data output, an acknowledgement that the parameter is has been set.

19. The computer program product of claim 10 , wherein the PWM signal line and the tachometric signal line are communicatively coupled to a baseboard management controller.

20. A computer program product including a computer readable medium, the computer program product comprising computer program instructions that, when executed, cause a computer to carry out the steps of:

receiving, from a requesting entity, a request to retrieve fan information from a fan unit;

determining a signal frequency of a pulse width modulated (PWM) signal associated with a type of the requested fan information, wherein the determined signal frequency is outside a frequency range used to control a fan speed of a fan in the fan unit;

sending the PWM signal at the determined signal frequency to the fan unit on a PWM signal line;

receiving the requested fan information as data output on a tachometric signal line from the fan unit; and

sending the requested fan information to the requesting entity.