User's Manual

Intel® 815 Chipset: Graphics Controller PRM, Rev 1.0
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Watermark and Burstlength Control MM 0x20D8
 Read the current value of the Watermark and Burstlength Control Register.
 Clear the burst length and watermark bits (bits 22:20, 17:12, 10:8 and 5:0).
 OR–in the saved value of the Watermark and Burstlength Control Register.
 Write the result back into the Watermark and Burstlength Control Register.
• Disable the low-priority ring buffer, in preparation for setting new values, by clearing the
RING_VALID bit in the Low-Priority Ring Buffer Length field at MM 0x203C.
 Read the current value of the Low-Priority Ring Buffer Length field (MM 0x203C).
 Clear the valid bit (bit 0).
 Write the result back into the Low-Priority Ring Buffer Length field.
• Set up the low-priority ring buffer.
 Write a 0 to the low-priority ring buffer tail at MM 0x2030.
 Write a 0 to the low-priority ring buffer head at MM 0x2034.
 Restore the low-priority ring buffer start at MM 0x2038, but preserve the reserved bits.
 Restore the Low-Priority Ring Buffer Length field, but preserve the Automatic Report Header
Pointer bits and set the Ring Buffer Valid flag.
• Turn on the screen.
• Relock the protected register space in order to complete the state restoration process.
At this point the graphics adapter should function completely, in the mode identified by the saved-state
information.