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Problem with RAM /RAS hold time. #4

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frozen-signal opened this issue Jul 15, 2023 · 3 comments · Fixed by #10
Closed

Problem with RAM /RAS hold time. #4

frozen-signal opened this issue Jul 15, 2023 · 3 comments · Fixed by #10
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bug Something isn't working IOU Related to the Apple IIe's IOU (344-0020)

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@frozen-signal
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As of writing, this is what is displayed with a real MMU and a IOU programmed with the sources of this repository:
image

Check if there is a bus conflict on RA0-RA7.
@frozen-signal frozen-signal mentioned this issue Jul 15, 2023
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@frozen-signal frozen-signal added bug Something isn't working IOU Related to the Apple IIe's IOU (344-0020) labels Jul 16, 2023
@frozen-signal
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Fixed several things in 47167a4, but the problem is still present.

@frozen-signal
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Testbenches confirms that the video scanner is correct, and the video address mux generates the correct addresses. The problem is possibly tied to RAM refresh timeouts.

See fd76e18

@frozen-signal
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This problem a problem with the multiplexed RAM address. Apple IIe's RAM need a /RAS hold time of ~25ns. With the current sources, it is close to 0ns.

A fix is underway.

Also changed the title of the issue.

@frozen-signal frozen-signal changed the title Possible bus contention or timing issue. Problem with RAM /RAS hold time. Jul 29, 2023
@frozen-signal frozen-signal mentioned this issue Jul 29, 2023
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bug Something isn't working IOU Related to the Apple IIe's IOU (344-0020)
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Fixed DRAM /RAS hold time frozen-signal/Apple_IIe_MMU_IOU
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