Read your 860 manual Chapter 12. Three times. The difference between a power on reset (PORESET*) and a pushbutton (hardware reset or software induced reset) involves reading the configuration off the data bus and starting the clocks (PLL).
When power is applied, the processor reads the configuration, sets up the PLLs, and lets them stabilize. On a pushbutton reset, the processor does NOT read the configuration and the clocks keep running however they were configured when power was applied.
I would be very suspicious that your PLLs are not stabilizing in time. This would most likely be due to an unstable input clock or possibly due to unstable or noisy power supply voltages.
From the 860 maunual, Chapter 12:
"When PORESET signal is negated, the MODCK values are sampled and internally latched. To ensure proper operation, the PORESET signal should be asserted for a minimum of 3 microseconds."
Question: Does your hardware ensure this?
"When a hard reset event occurs, the MPC860 determines its initial mode of operation by sampling the values present on the data bus (D[0Ð31])..."
Question: Does your hardware ensure the data bus lines are driven properly until after the initial mode of operation is established? Note that the manual says the processor leaves the reset state after PORESET is released _AND_ the PLLs are stable. PLL instability could stretch your start up time, causing problems.
Question: Is your RSTCONF* being driven properly?
gvb
At 02:50 PM 1/17/2003 -0500, bren@sjtu.edu.cn wrote:
We have a very very weird problem. When we power-on our MPC860 board, u-boot will stuck before running in RAM. But once we reset the board with the "reset push button", everything will be fine as long as we DO NOT power-off.
Obviously, there are some differences between power-on reset and internal hardware reset and those differences are where we make some mistakes.
Can anyone help us?
Thanks.
Laudney Ren
-- An expert is one who knows more and more about less and less until he knows absolutely everything about nothing.
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