Error instantiating PLL

from nmigen import *
from nmigen_boards.icebreaker import ICEBreakerPlatform

class Example(Elaboratable):

    def elaborate(self, platform):
        clk12 = platform.request('clk12')
        led = platform.request('user_led')
        pll_clk = Signal()
        pll_lock = Signal()
        counter = Signal(25)
        cd_pll = ClockDomain('pll')
        pll = Instance('SB_PLL40_PAD',
            p_FEEDBACK_PATH='SIMPLE',
            p_DIVR=0b0000,
            p_DIVF=0b1001111,
            p_DIVQ=0b100,
            p_FILTER_RANGE=0b001,
            i_PACKAGEPIN=clk12,
            o_PLLOUTGLOBAL=pll_clk,
            o_LOCK=pll_lock,
            i_RESETB=Signal(reset=1),
            i_BYPASS=Signal(reset=0))
        m = Module()
        m.domains.pll = cd_pll
        m.submodules += pll
        m.d.comb += cd_pll.clk.eq(pll_clk)
        m.d.pll += counter.eq(counter + 1)
        m.d.comb += led.eq(counter[counter.nbits - 1])
        return m

ICEBreakerPlatform().build(Example(), do_program=True)

# Fails with
#
#     ERROR: PLL '$3' has a PACKAGEPIN driven by an SB_GB, should be directly connected to an input SB_IO.D_IN_0 port
#     ERROR: Packing design failed.
#     0 warnings, 2 errors
#     Traceback (most recent call last):
#       File "example3.py", line 39, in <module>
#         ICEBreakerPlatform().build(Example(), do_program=True)
#       File "/Users/kbob/Documents/Code/github/m-labs/nmigen/nmigen/build/plat.py", line 74, in build
#         products = plan.execute_local(build_dir)
#       File "/Users/kbob/Documents/Code/github/m-labs/nmigen/nmigen/build/run.py", line 98, in execute_local
#         subprocess.check_call(["sh", "{}.sh".format(self.script)])
#       File "/opt/local/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/subprocess.py", line 347, in check_call
#         raise CalledProcessError(retcode, cmd)
#     subprocess.CalledProcessError: Command '['sh', 'build_top.sh']' returned non-zero exit status 255.