Re: question in the function navmess(int prn, int ch)
Clifford Kelley <[email protected]> Wed, 29 Apr 2009 19:06:59 -0700 (GMT-07:00)
| Newsgroups | gmane.comp.hardware.gps.opensource |
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| Message-ID | <25394462.1241057219832.JavaMail.root@elwamui-hound.atl.sa.earthlink.net> |
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<P>This part of the code takes the packed data bits (one bit per channel)&n=
bsp; and assembles it into the 30 bit words and subframes. One frame =
is converted into a navigation message.</P>
<P>Cliff<BR><BR><BR></P>
<BLOCKQUOTE style=3D"PADDING-LEFT: 5px; MARGIN-LEFT: 0px; BORDER-LEFT: #000=
0ff 2px solid">-----Original Message----- <BR>From: =E8=A2=81=E5=85=86=E5=
=A5=8E <[email protected]><BR>Sent: Apr 24, 2009 1:07 AM <BR>To: cwkelley@e=
arthlink.net <BR>Cc: [email protected] <BR>Subject: questio=
n in the function navmess(int prn, int ch) <BR><BR>hello everyone:<BR><BR>&=
nbsp; I=E3=80=80have a question in the function "void navmess (=
int prn, int ch)" in file gpsfuncs.c which has troubled me for quite a bit =
of time. In this function, there is a loop as follows:<BR><BR><FONT size=3D=
2> for (sfr =3D 1; sfr <=3D 5; sfr++)<BR> &=
nbsp; {<BR> /* sfptr=E7=A7=BB=E5=88=B0=
=E6=9F=90=E4=B8=80=E4=B8=AA=E5=AD=90=E5=B8=A7 */<BR> &nbs=
p; sfptr =3D sf[sfr] + 1;<BR><BR>  =
; /* =E9=81=8D=E5=8E=86=E6=AF=8F=E4=B8=80=E4=B8=AA=E5=AD=97 */<BR>&nb=
sp; for (word =3D 1; word <=3D 10; word++=
)<BR> {<BR> &n=
bsp; scale =3D 0x20000000L; /* =E4=BA=8C=E8=
=BF=9B=E5=88=B6=E4=B8=BA100000000000000000000000000000=EF=BC=8C30=E4=BD=8D =
*/<BR> *sfptr =3D 0=
;<BR><BR> /* =E9=81=
=8D=E5=8E=86=E6=9F=90=E4=B8=80=E4=B8=AA=E5=AD=97=E7=9A=8430bit */<BR> =
for (i =3D 0; i < 30;=
i++)<BR> {<BR>&nbs=
p; if =
(*data_msg_ptr & chmask)<BR>  =
; *sfptr |=3D scale;<BR>&=
nbsp; =
<BR> &n=
bsp; scale =3D scale >> 1;<BR> &=
nbsp; data_msg_ptr++;<BR> =
}<BR> &=
nbsp; sfptr++;<BR> =
}<BR> }</FONT><BR><BR> I am so wondered=
now about this loop, can anyone give me some explanation? Thank you first!=
<BR><BR>  =
; &nb=
sp; &=
nbsp; yours sincrcely,<BR> &nbs=
p; &=
nbsp; &nbs=
p; &=
nbsp; &nbs=
p; &=
nbsp; Yuan Zhaokui<BR><BR><BR><ZZZ!-- -- footer><BR><SPAN=
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