LH79520 interrupt problem

hi, I'm using a custom designed board having LH79520 with 32MB micron SDRAM & 8MB flash. Very similar to LogicPD board, but without the extras (lan, audio, CPLD, buffers etc). It does have a external reset chip.

The board works fine when no interrupts are used. However, when I try to use the timer interrupt, it works intermittently between power-ups. Meaning, the interrupt is working after a power-up on some occasions and doesn't on other occasions. But once the interrupt starts to work after a power-up, it will keep working until the next power cycle to the board. I've verified that the timer itself is configured properly and always counts, irrespective of whether interrupt is working or not.

I'm using standard Sharp ABL/CSP/BSP software package.

Please help!!

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What do you mean by doesn't work? Is it that the interrupt is never serviced, the code crashes to unknown locations, etc. More detail is needed. Does the code work on the LogicPD board, or are there differences that prevent the same code from working on both boards?


Reply to
Not Really Me

We struggled with the same problem for months before a solution was found. Sharp denied that there was a problem but eventually included the correct wiring suggestion in the LH79525 manual.

The hardware people pointed at the software and the software people pointed at the hardware. Eventually it was determined to be a hardware issue.

From the hardware designed who was able to find the solution:

Early designs with the Sharp LH79520 had intermittent boot-up problems that seemed to be related to power supply sequencing (3.3V and 1.8V). We logically added the Reset signal to the TRST line in the JTAG input to the CPU. This trick was found in the errata for one of the newer members of the Sharp processor family. We removed the various (unnecessary) delays in the power supply enables of previous designs. We left the 100 Ohm resistive load on the 1.8V supply to discharge the output capacitor when power was removed for a short period of time.

Good Luck, Dave

Reply to
David Roethig

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