164 lines
5.2 KiB
C++
164 lines
5.2 KiB
C++
#include "precomp.h"
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//
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// SHM.CPP
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// Shared Memory Access, cpi32 and display driver sides both
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//
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// Copyright(c) Microsoft 1997-
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//
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#define MLZ_FILE_ZONE ZONE_CORE
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//
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// WAIT_FOR_BUFFER
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//
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// Wait until the display driver is accessing the new buffer.
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//
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// There are logically 8 states for a set of 3 boolean variables. We can
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// cut this down to 4 by some simple analysis:
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//
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// - The overall busy flag overrides the other flags if it is clear.
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// - We can never have the display driver in both buffers (it's single
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// threaded).
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//
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// So the 4 states are as follows.
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//
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// STATE BUSY FLAGS DISPLAY DRIVER STATE
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// New Old Overall
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//
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// 1 0 0 0 Not using shared memory
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// 2 0 0 1 Using shared memory (wait to see which)
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// 3 1 0 1 Using the new buffer
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// 4 0 1 1 Using the old buffer
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//
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// Obviously we wait while states 2 or 4 hold true....
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//
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#define WAIT_FOR_BUFFER(MEMORY, NEWBUFFER, OLDBUFFER) \
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while ( g_asSharedMemory->MEMORY.busyFlag && \
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( g_asSharedMemory->MEMORY.bufferBusy[OLDBUFFER] || \
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!g_asSharedMemory->MEMORY.bufferBusy[NEWBUFFER] ) ) \
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{ \
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TRACE_OUT(("Waiting for SHM")); \
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Sleep(0); \
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}
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//
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// SHM_SwitchReadBuffer - see shm.h
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//
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void SHM_SwitchReadBuffer(void)
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{
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int oldBuffer;
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int newBuffer;
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DebugEntry(SHM_SwitchReadBuffer);
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//
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//
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// BUFFER SWITCHING FOR THE DISPLAY DRIVER -> SHARE CORE DATA
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//
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//
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// This is a forced switch. The Share Core calls this function only
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// when it wants to force the switching of the buffers used to pass the
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// data back from the display driver.
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//
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//
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// ÉÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍ»
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// º Kernel to Share Core data block º
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// º ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ º
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// º ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿ ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿ º
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// º ³ ³ BUSY FLAG1 ³ ³ º
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// º ³ Share Core ³ 1 ³ Display Driver³ º
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// º ³ ³ ³ ³ º
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// º ³ (read buffer) ³ SWITCH ³ (write buffer)³ º
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// º ³ ³ ³ ³ ³ º
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// º ³ ³<ÄÄÄÄÄÄÁÄÄÄÄÄÄ>³ ³ º
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// º ³ BUSY FLAG2 ³ ³ BUSY FLAG2 ³ º
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// º ³ 0 ³ ³ 1 ³ º
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// º ³ ³ IN USE ³ ³ º
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// º ³ ³ ³ ³ ³ º
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// º ³ ³ ÀÄÄÄÄÄÄ>³ ³ º
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// º ³ ³ ³ ³ º
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// º ³ ³ ³ ³ º
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// º ³ ³ COUNT ³ ³ º
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// º ³ ³ 5 ³ ³ º
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// º ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ º
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// º º
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// º º
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// ÈÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍͼ
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//
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//
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// On entry it is safe to clean out the current read buffer (to leave
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// it in a virgin state for the display driver once the buffers have
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// switched).
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//
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// The logic for the switch is as follows.
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//
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// - Set the new value for the SWITCH pointer
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//
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// - If the shared memory BUSY FLAG1 is clear we've finished and can
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// exit now.
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//
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// - We can exit as soon as either of the following are true.
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//
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// - BUSY FLAG1 is clear DDI has finished
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// - BUSY FLAG1 is set AND BUSY FLAG2 is set DDI is in new memory
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//
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//
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//
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// Check for a valid pointer
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//
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ASSERT(g_asSharedMemory);
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//
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// Do that switch...The display driver may be in the middle of an
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// access at the moment, so we will test the state afterwards.
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//
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oldBuffer = g_asSharedMemory->displayToCore.newBuffer;
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newBuffer = 1 - oldBuffer;
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g_asSharedMemory->displayToCore.newBuffer = newBuffer;
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WAIT_FOR_BUFFER(displayToCore, newBuffer, oldBuffer);
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DebugExitVOID(SHM_SwitchReadBuffer);
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}
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//
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// SHM_SwitchFastBuffer - see shm.h
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//
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void SHM_SwitchFastBuffer(void)
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{
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int oldBuffer;
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int newBuffer;
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DebugEntry(SHM_SwitchFastBuffer);
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//
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// Check for a valid pointer
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//
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ASSERT(g_asSharedMemory);
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//
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// Do that switch...The display driver may be in the middle of an
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// access at the moment, so we will test the state afterwards.
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//
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oldBuffer = g_asSharedMemory->fastPath.newBuffer;
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newBuffer = 1 - oldBuffer;
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g_asSharedMemory->fastPath.newBuffer = newBuffer;
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//
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// Wait for completion
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//
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WAIT_FOR_BUFFER(fastPath, newBuffer, oldBuffer);
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DebugExitVOID(SHM_SwitchFastBuffer);
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}
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