8. Initialization
reset the processor after the initial power-on, or whenever power or SysClk are interrupted.
The Power-on Reset sequence is as follows:
- The external agent negates DCOk.
- The external agent asserts SysReset*.
- The external agent negates SysGnt*.
- The external agent negates SysRespVal*.
- Once Vcc, VccQ[SC,Sys], Vref[SC,Sys], Vcc[Pa,Pd], and SysClk stabilize, the external agent waits at least 1ms and then asserts DCOk.
- At this time, the System interface resides in slave state and all internal state is initialized.
- The SysClkDiv mode bits default to divide-by-1.
- The SCClkDiv mode bits default to divide-by-3.
- After waiting at least 100 ms for the internal clocks to stabilize, the external agent loads the mode bits into the processor by driving the mode bits on SysAD[63:0], waiting at least two SysClk cycles, and then asserting SysGnt* for at least one SysClk cycle.
- After waiting at least another 100 ms for the internal clocks to restabilize, the external agent synchronizes all clocks internal to the processor. This is performed by asserting SysRespVal* for one SysClk cycle.
- After waiting at least 100 ms for the internal clocks to again restabilize, (a third 100 ms restabilization period) the external agent negates SysReset*.
- The external agent must retain mastership of the System interface, refrain from issuing external requests or nonmaskable interrupts, and ignore the system state bus until the processor asserts SysReq*. The assertion of SysReq* indicates the processor is ready for operation. In a cluster arrangement, all processors must assert SysReq*, indicating they are ready for operation.
If the virtual SysClk is used during the reset sequence, the mode bits, SysGnt*, SysRespVal*, and SysReset* should all be referenced to the virtual SysClk that is created with SysCyc*. This approach will cause the R10000 to come out of reset synchronously with the virtual SysClk, which will allow repeatable and lock-step operation (see Chapter 6, the section titled "Support for Hardware Emulation," for description of virtual SysClk operation). (See page 148 of the Errata.)