Visible to Intel only — GUID: iga1401398645874
Ixiasoft
Visible to Intel only — GUID: iga1401398645874
Ixiasoft
23.2. Functional Description
The interval timer core has two user-visible features:
- The Avalon® Memory-Mapped ( Avalon® -MM) interface that provides access to six 16-bit registers
- An optional pulse output that can be used as a periodic pulse generator
All registers are 16-bits wide, making the core compatible with both 16-bit and 32-bit processors. Certain registers only exist in hardware for a given configuration. For example, if the core is configured with a fixed period, the period registers do not exist in hardware.
The following sequence describes the basic behavior of the interval timer core:
- An Avalon® -MM host peripheral, such as a Nios® II or Nios® V processor, writes the core's control register to perform the following tasks:
- Start and stop the timer
- Enable/disable the IRQ
- Specify count-down once or continuous count-down mode
- A processor reads the status register for information about current timer activity.
- A processor can specify the timer period by writing a value to the period registers.
- An internal counter counts down to zero, and whenever it reaches zero, it is immediately reloaded from the period registers.
- A processor can read the current counter value by first writing to one of the snap registers to request a coherent snapshot of the counter, and then reading the snap registers for the full value.
- When the count reaches zero, one or more of the following events are triggered:
- If IRQs are enabled, an IRQ is generated.
- The optional pulse-generator output is asserted for one clock period.
- The optional watchdog output resets the system.