RADEON_RBBM_FIFOCNT_MASK
int slots = INREG( ai->regs, RADEON_RBBM_STATUS ) & RADEON_RBBM_FIFOCNT_MASK;
int slots = INREG( di->regs, RADEON_RBBM_STATUS ) & RADEON_RBBM_FIFOCNT_MASK;