REG_SPR
bus_write_1(bar->b_res, REG_SPR, REG_ACR);
bus_write_1(bar->b_res, REG_SPR, 0);
v0 = bus_read_1(bar->b_res, REG_SPR);
bus_write_1(bar->b_res, REG_SPR, 0x80 + -cfg->clock);
v1 = bus_read_1(bar->b_res, REG_SPR);