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furon

Lpc Abort Cycle

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As we know, v1.2-1.4 Xboxes don't have an easily-accessible LFRAME# signal, so modchips work on the assumption that the southbridge will never abort a cycle early by asserting LFRAME# and driving 0b1111 onto LAD[3:0]. That may be true for memory read cycles, but what about memory writes and I/O read/write cycles? Besides a timeout (which shouldn't happen anyway if long wait states are used), is there ever a case where the MCPX might abort an LPC cycle?

EDIT: I may have posted this in the wrong section. I need this info for a hardware mod, but it might be better suited in the Modchip or General forum. Sorry about that.

Edited by furon

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Looking at the LPC spec again, I realized it doesn't matter anyway, because LFRAME# is absolutely required in order to recognize I/O read cycles, which put 0b000 on LAD during the CYCTYPE+DIR phase. A modchip would skip both START and CYCTYPE+DIR, then recognize the first non-zero I/O port adress nibble as the start of a transaction.

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Board startup date: April 23, 2017 12:45:48
  • Similar Content

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      LPC diagnostics (v0.1) Tutorial written by : milingo
      Last edited: August 5, 2004
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      picture by Please login or register to see this link.
       
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      Please login or register to see this link.
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      If you need to contact me try thru xbox-scene forum....
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      Tutorial written by : milingo
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