Intel manual Intel 815 Chipset Graphics Controller PRM, Rev

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.

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