Writing Device Drivers

Testing the Polled I/O Interfaces

The polled I/O interfaces are only available under the following circumstances:

The polled I/O interfaces only become available at a certain point in the boot process. Polled I/O requests issued from the OpenBoot PROM before the system is running are not rendered. Similarly, kmdb prompts issued before the console is configured are not rendered.

To test the polled I/O interfaces, enter the OpenBoot PROM by using the L1+A keystroke sequence. To validate that the polled I/O interfaces are being used, type the following command at the OpenBoot PROM ok prompt:

ok 1b emit ." [32m This is a test" 1b emit ." [m"

The polled I/O interfaces are working properly if the following statements are true: