While reset is applied, HOST_IRQ will reset to tri-state (an external pullup pulls the line high).
HOST_IRQ will remain tri-state (pulled high externally) until the microprocessor boot completes. While the signal is pulled high, this indicates that the DLPC150 controller is performing boot-up and auto-initialization.
As soon as possible after boot-up, the microprocessor will drive HOST_IRQ to a logic high state to indicate that the DLPC150 controller is continuing to perform auto-initialization (no real state change occurs on the external signal).
Upon completion of auto-initialization, software will set HOST_IRQ to a logic low state to indicate the completion of auto-initialization. At the falling edge, the system is said to enter the INIT_DONE state.
After auto-initialization completes, HOST_IRQ is used to generate a logic high interrupt pulse to the host through software control. This interrupt indicates that the DLPC150 controller has detected an error condition or otherwise requires service.