SDMA0_GFX_RB_RPTR
WREG32(SDMA0_GFX_RB_RPTR + reg_offset, 0);
reg = SDMA0_GFX_RB_RPTR + SDMA0_REGISTER_OFFSET;
reg = SDMA0_GFX_RB_RPTR + SDMA1_REGISTER_OFFSET;