Compaq EV68A specifications Power-Up Reset Flow and the ResetL and Dcokh Pins, Constraints

Power-Up Reset Flow and the Reset_L and DCOK_H Pins

1.The clock forwarding and system clock ratio configuration information is loaded onto the 21264/EV68A. See Section 7.1.2.

2.The internal PLL is ramped up to operating frequency.

3.The internal arrays built-in self-test (BiST) is run, followed by Icache initialization using an external serial ROM (SROM) interface.

The 21264/EV68A systems, unlike the Alpha 21064 and 21164 microprocessor systems, are required to have an SROM. The SROM provides the only means to configure the system port, and the SROM pins can be used as a software-controlled UART.

The Icache must contain PALcode that starts at location 0x780. This code is used to configure the 21264/EV68A IPRs as necessary before causing any offchip read or write commands. This allows the 21264/EV68A to be configured to match the external system implementation.

4.After configuring the 21264/EV68A, control can be transferred to code anywhere in memory, including the noncacheable regions. The Icache can be flushed by a write operation to the ITB invalidate-all register after control is transferred. This transfer of control should be to addresses not loaded in the Icache by the SROM interface or the Icache may provide unexpected instructions.

5.Typically, any state required by the PALcode is initialized and then the console is started (switching out of PALmode and into native mode). The console code initial- izes and configures the system and boots an operating system from an I/O device such as a disk or the network.

Figure 7–1shows the sequence of events at power-up, or cold reset. In Figure 7–1,note the following symbols for constraints and information:

Constraints:

ASetup (A0) and hold (A1) for IRQ’s to be latched by DCOK (2 ns for each).

BEnough time for Reset_L to propagate through 5 stages of RESET synchronizer (clocked by the inter- nal framing clock, which is driven by EV6Clk_x). Worst case for the 21264/EV68A would be 5x8x15 = 600 GCLK cycles.

CMin = 1 FrameClk cycle.

Information:

a8 GCLK cycles from DCOK assertion to first “real” EV6Clk_x cycle.

bApproximately 525 GCLK cycles for external framing clock to be sampled and captured.

c1 FrameClk_x cycle.

d3 FrameClk_x cycles.

eApproximately 264 GCLK cycles to prevent first command from appearing too early.

fApproximately 700,000 GCLK cycles for BiST + approximately 100,000 GCLK cycles fixed time + approximately 50,000 GCLK cycles per line of Icache for SROM load.

g16 GCLK cycles.

7–2 Initialization and Configuration 21264/EV68A Hardware Reference Manual