Root/prod/doc/analysis.html

Source at commit cb855b2a6902a516dd58d7bb1f074f9d50ff39b1 created 8 years 8 months ago.
By Werner Almesberger, prod/doc/: added voltage measurement points on layout
1<TITLE>Production and testing: Fault analysis</TITLE>
2<BODY>
3<HTML>
4<H1>Production and testing: Fault analysis</H1>
5
6
7<!-- ====================================================================== -->
8
9
10<H2>Component placement and orientation</H2>
11
12
13<!-- ====================================================================== -->
14
15
16<H2>Supply voltages</H2>
17
18The transceiver has three voltage domains:
19<UL>
20  <LI>The supply and I/O voltage, which is nominally 3.3 V in
21    <B>atben</B> and <B>atusb</B>,
22  <LI>the digital (core) supply, which is nominally 1.8 V, and
23  <LI>the analog (RF) supply, which is nominally 1.8 V.
24</UL>
25<BR>
26On <B>atusb</B>, there is also the USB voltage domain at nominally 5.0 V.
27<P>
28Voltages should be tested in the following order: USB, then I/O, then
29digital, and finally analog. The table below gives the permissible
30ranges. Any voltages outside of these ranges indicate a problem.
31<P>
32<TABLE frame="border" cellpadding="2">
33  <TR><TH>Domain<TH>Nominal<TH>Minimum<TH>Maximum
34  <TR><TD>USB<TD>5.0 V<TD>4.5 V<TD>5.25 V
35  <TR><TD>I/O<TD>3.3 V<TD>3.0 V<TD>3.6 V
36  <TR><TD>Digital<TD>1.8 V<TD>1.7 V<TD>1.9 V
37  <TR><TD>Analog<TD>1.8 V<TD>1.7 V<TD>1.9 V
38</TABLE>
39<P>
40
41
42<!-- ---------------------------------------------------------------------- -->
43
44
45<H3>Measurement setup</H3>
46
47The measurements should be performed with a digital multimeter.
48The transceiver's analog and digital supplies (1.8 V) are only
49activated when sending or receiving.
50To enable all voltage domains, put the transceiver in receive mode:
51<PRE>
52atrf-txrx
53</PRE>
54or
55<PRE>
56atrf-txrx -d net:ben
57</PRE>
58Exit with Ctrl-C.
59<P>
60To produce periodic transmissions in addition to enabling all voltage
61domains, use
62<PRE>
63atrf-txrx -p 3 -E 0
64</PRE>
65or
66<PRE>
67atrf-txrx -d net:ben -p 3 -E 0
68</PRE>
69Again, exit with Ctrl-C. Note that the transmissions may disturb nearby
70equipment operating in the 2.4 GHz band, such as 802.11 networks. This
71can be prevented by shorting the antenna to ground.
72<P>
73In case the board does not accept commands, only the USB and I/O voltage
74can be checked. If they are correct, proceed with checking the clock.
75
76
77<!-- ---------------------------------------------------------------------- -->
78
79
80<H3>Measurement points on atben</H3>
81
82<P>
83<A href="atben-B.png"><IMG src="atben-B-small.png"></A>
84<P>
85
86
87<!-- ---------------------------------------------------------------------- -->
88
89
90<H3>Measurement points on atusb</H3>
91
92<P>
93<A href="atusb-B.png"><IMG src="atusb-B-small.png"></A>
94<P>
95
96
97<!-- ====================================================================== -->
98
99
100<H2>Clock frequency</H2>
101
102The flawless performance of the crystal oscillator is crucial for
103operation. Anomalies are easy to detect with even a low-cost oscilloscope
104and pinpoint specific problems and help to select further analysis steps.
105<P>
106The crystal used in <B>atben</B> and <B>atusb</B> has a nominal tolerance
107of +/&minus; 15 ppm at 22-28 C. Low-cost oscilloscopes typically have a timing
108accuracy of
109+/&minus; 100 ppm, which means that only major excursions can be detected by
110measuring the clock output with such an instrument. Full-speed USB only
111requires an accuracy of +/&minus; 2500 ppm.
112We can therefore consider all results within a range of +/&minus; 1000 ppm as
113sufficient, and perform more precise measurements by other means. This
114applies to <B>atben</B> as well as to <B>atusb</B>.
115
116
117<!-- ---------------------------------------------------------------------- -->
118
119
120<H3>Measuring the clock on atben</H3>
121
122<B>atben</B> normally does not output a clock signal. A 1 MHz clock
123can be enabled with the following command:
124<PRE>
125atrf-txrx -d net:ben -C 1
126</PRE>
127This configures <B>atben</B> as a promiscuous receiver. The reception
128of any IEEE 802.15.4 frame or pressing Ctrl-C will terminate the command.
129<P>
130The clock signal (CLKM) is available on the test pad shown here:
131<P>
132<A href="atben-A.png"><IMG src="atben-A-small.png"></A>
133<P>
134<TABLE frame="border" cellpadding="2">
135<TR><TH align="left">Clock<TH align="left">Action
136<TR><TD>0 Hz<TD>Check voltages; check that the clock is enabled;
137  check for shorts around crystal; check connectivity of crystal
138<TR><TD>0.999-1.001 MHz, ~3.3 Vpp<TD>Perform precision measurement with
139  <B>atrf-xtal</B>
140<TR><TD>Other<TD>Check voltages; check for contamination around crystal
141</TABLE>
142<P>
143
144
145<!-- ---------------------------------------------------------------------- -->
146
147
148<H3>Measuring the clock on atusb</H3>
149
150The transceiver provides the clock for the microcontroller in <B>atusb</B>.
151A clock signal is therefore always available. Immediately after reset,
152the transceiver generates a 1 MHz clock. When the microcontrolled comes out
153of reset, it raises the transceiver's clock output to 8 MHz and then
154enables USB.
155<P>
156The clock signal is available at the terminals of several components,
157either as the direct output from the transceiver (CLKM) or after passing
158a low-pass filter (CLK):
159<P>
160<A href="atusb-A.png"><IMG src="atusb-A-small.png"></A>
161<P>
162<TABLE frame="border" cellpadding="2">
163<TR><TH align="left">Clock<TH align="left">Action
164<TR><TD>0 Hz<TD>Check voltages; check for shorts around crystal; check
165  connectivity of crystal
166<TR><TD>0.999-1.001 MHz, ~3.3 Vpp<TD>Check presence of firmware; check for
167  shorts on SPI signals; check connectivity of SPI signals
168<TR><TD>7.992-8.008 MHz, ~3.3 Vpp<TD>Perform precision measurement with
169  <B>atrf-xtal</B>
170<TR><TD>Other<TD>Check voltages; check for contamination around crystal
171</TABLE>
172<P>
173Note that, if testing a board into which no boot loader has been flashed
174yet, the clock frequency should be 1 MHz. If an unsuccessful attempt has
175been made to flash the boot loader, the frequency may be 1 MHz or 8 MHz,
176depending on how much code was successfully flashed.
177
178
179<!-- ---------------------------------------------------------------------- -->
180
181
182<H3>Precision measurements</H3>
183
184The clock frequency of <B>atben</B> can be measured with an accuracy
185of about +/&minus; 100 ppm using the program <B>atrf-xtal</B>. <B>atrf-xtal</B>
186runs directly on the Ben and measures the duration of packet transmissions.
187The transmission time depends on the bit clock which is in turn derived
188from the oscillator.
189<PRE>
190atrf-xtal 100
191</PRE>
192The number reported is the number of poll loops the CPU counted. This
193value should be compared to a reference count obtained with a known to
194be good <B>atben</B> board on the same Ben at a comparable temperature.
195<P>
196<TABLE frame="border" cellpadding="2">
197<TR><TH align="left">Difference<TH align="left">Action
198<TR><TD>&gt; +/&minus; 50 ppm<TD>Correct operation
199<TR><TD>&lt; &minus;80 ppm<TD>Check soldering of capacitors;
200  check for contamination around crystal
201<TR><TD>&gt; +120 ppm<TD>idem
202<TR><TD>Other<TD>Divergence can be compensated by adjusting trim value
203</TABLE>
204
205<P>
206<HR>
207Up: <A href="index.html">Production and testing</A>&nbsp;
208Prev: <A href="test.html">Functional test</A>&nbsp;
209<HR>
210Last update: 2011-05-26&nbsp;&nbsp;<I>Werner Almesberger</I>
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