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eg25-gps-init: improve docs

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This commit is contained in:
Colin 2023-08-21 11:14:16 +00:00
parent fabd1e3b64
commit 79777cd4ae
1 changed files with 15 additions and 5 deletions
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20
hosts/by-name/moby/eg25_gps_init.py
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@ -7,11 +7,20 @@
#
# this script downloads assisted GPS (AGPS) data via the system's default gateway (i.e. WiFi)
# and shares that with the modem. this quickens the process of acquiring a GPS fix.
# even with AGPS, an indoor fix is generally not possible (though i have seen the receiver
# locate a _single_ satellite from indoors -- not enough for a fix).
# even an outdoor fix within a suburban setting may take 10 minutes.
#
# expects to run on megi's kernel, with `CONFIG_MODEM_POWER=y`
# this script expects to run on megi's kernel, with `CONFIG_MODEM_POWER=y`.
#
# EXPECTATIONS/TIPS:
# - with the right environment, you may get a GPS fix in < 30s.
# - indoors, you shouldn't expect to *ever* get a cold-start GPS fix.
# - maybe you'll track 1 satellite if lucky: enough to receive GPS time but not for a GPS fix.
# - get a fix outdoors, then walk indoors: GPS is smart enough to maintain a spotty fix.
# - outdoors in suburbia, a fix might take 10-20 minutes.
# - i have better luck *placing my phone on the roof of my car* than holding it in the air with my hand.
# - maybe a big metal plate opposite the sky acts as a dish/antenna?
# - in Seattle, i track several GLONASS and GPS sats: about an even split.
# - the GPS sats have better SNR.
# - modem seems to not show any BeiDou or Galileo sats even if i enable them.
#
# eg25 modem/GPS docs:
# [GNSS-AP-Note]: https://wiki.pine64.org/images/0/09/Quectel_EC2x%26EG9x%26EG2x-G%26EM05_Series_GNSS_Application_Note_V1.3.pdf
@ -36,7 +45,8 @@ import time
POWER_ENDPOINT = "/sys/class/modem-power/modem-power/device/powered"
# GNSS-AP-Note 1.4:
# also at xtrapath5 and xtrapath6 subdomains
# also at xtrapath5 and xtrapath6 subdomains.
# the AGPS data here is an almanac good for 7 days.
AGPS_DATA_URI_BASE = "https://xtrapath4.izatcloud.net"
class AgpsDataVariant: