tnt has submitted this change. ( https://gerrit.osmocom.org/c/osmo-e1-hardware/+/27895 )

Change subject: icE1usb fw/gpsdo: Limit the fine tuning range ......................................................................

icE1usb fw/gpsdo: Limit the fine tuning range

Fine tuning has a limited tuning range. If at some point we hit the limits, we need to bit the bullet and try to 'transfer' some of that to the coarse range as best as we can. Hopefully we get it close enough to limit disruption.

Note that this should really never happen because although it's limited, the tuning range should be good enough to absorb any reasonable temperature / aging variation once we have coarse tuned.

Signed-off-by: Sylvain Munaut tnt@246tNt.com Change-Id: I2d9d348f5466f581b3d6d36c98847c47e2452f98 --- M firmware/ice40-riscv/icE1usb/gpsdo.c 1 file changed, 16 insertions(+), 1 deletion(-)

Approvals: laforge: Looks good to me, but someone else must approve tnt: Looks good to me, approved Jenkins Builder: Verified

diff --git a/firmware/ice40-riscv/icE1usb/gpsdo.c b/firmware/ice40-riscv/icE1usb/gpsdo.c index 057490f..c1df4b0 100644 --- a/firmware/ice40-riscv/icE1usb/gpsdo.c +++ b/firmware/ice40-riscv/icE1usb/gpsdo.c @@ -240,8 +240,23 @@ g_gpsdo.fine.div = 0; }

- /* Apply value with a bias from long term accumulator */ + /* Compute value with a bias from long term accumulator */ tune = g_gpsdo.tune.fine - (g_gpsdo.fine.acc / 2); + + /* If fine tune is getting close to boundary, do our + * best to transfer part of it to coarse tuning */ + if ((g_gpsdo.tune.fine < 512) || (g_gpsdo.tune.fine > 3584)) + { + int coarse_adj = ((int)g_gpsdo.tune.fine - 2048) >> 6; + + g_gpsdo.tune.coarse += coarse_adj; + g_gpsdo.tune.fine -= coarse_adj << 6; + tune -= coarse_adj << 6; + + pdm_set(PDM_CLK_HI, true, g_gpsdo.tune.coarse, false); + } + + /* Apply fine */ pdm_set(PDM_CLK_LO, true, tune, false);

/* Debug */