PDC_SYS_CTL
scr = ioread32(mmio_base + PDC_SYS_CTL);
iowrite32(scr | (0x01 << 14), mmio_base + PDC_SYS_CTL);
ioread32(mmio_base + PDC_SYS_CTL); /* flush */
scr = ioread32(mmio_base + PDC_SYS_CTL);
iowrite32(scr & ~(0x01 << 14), mmio_base + PDC_SYS_CTL);
ioread32(mmio_base + PDC_SYS_CTL); /* flush */