FreeCalypso > hg > freecalypso-schem2
comparison venus/doc/Star-points-in-core @ 35:971c05950675
starpoints in core: commit to using pcb-rnd intnoconn
author | Mychaela Falconia <falcon@freecalypso.org> |
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date | Mon, 22 Nov 2021 09:54:48 +0000 |
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34:dfa0d08d8f2b | 35:971c05950675 |
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1 iWOW's TR-800 module, whose reverse-engineered PCB layout will serve as a | |
2 reference for the Calypso core of FC Venus, is nothing but a mass-produced | |
3 version of TI's Leonardo reference design. We don't have any original PCB | |
4 layout files for Leonardo, but we do have schematics, in 3 different versions: | |
5 | |
6 ftp://ftp.freecalypso.org/pub/GSM/Calypso/Leonardo_plus_RD122.pdf | |
7 ftp://ftp.freecalypso.org/pub/GSM/Calypso/Leonardo_plus_quadband_schem.pdf | |
8 ftp://ftp.freecalypso.org/pub/GSM/Calypso/Leonardo_rev05.pdf | |
9 | |
10 TR-800 is based on quadband Leonardo+ (that's what makes it interesting), but | |
11 the hobbled 2-band version of Leonardo is the only one for which we have TI's | |
12 original DSN (OrCAD) schematic file, in addition to the corresponding PDF: | |
13 | |
14 ftp://ftp.freecalypso.org/pub/GSM/Calypso/Leonardo_rev05.dsn | |
15 | |
16 TI's group in Aalborg (Denmark) that designed and built their development boards | |
17 used OrCAD for schematics and PADS for PCB layout. We have their PADS PCB | |
18 design file for a different board from about the same time frame (E-Sample), | |
19 but not for any Leonardo variant. | |
20 | |
21 If you look at the baseband page of Leonardo schematics (this part is the same | |
22 in all 3 versions), you will see 3 symbols denoting star routing: HST201 and | |
23 HST202 (labeled "STAR_CONFIG") split V-DBB net into VDD-PLL and VDD-CORE | |
24 branches, and HST203 (labeled "GND_POINT") creates a special ground for the | |
25 32.768 kHz oscillator circuit, connected to the rest of board ground at just | |
26 one point. | |
27 | |
28 This star routing in TI's reference version of Calypso/Leonardo core exists not | |
29 only in TI's schematics, but also in the physical PCB layout which we have | |
30 recovered from TR-800 by reverse engineering. If you look at the Gerber files | |
31 which we received from the PCB RE company (published on our FTP site in 2021), | |
32 specifically the OKPCBM~1.G1 gerber file corresponding to the inner layer just | |
33 below the surface (L2 or L5 depending on which way you count), you can see the | |
34 physical features that were once produced, presumably in PADS, to effect the | |
35 star routing depicted in the schematics. | |
36 | |
37 The physical PCB star routing feature corresponding to HST201 & HST202 resides | |
38 just underneath C214 footprint. There is a microvia (blind via going only one | |
39 layer in) inside C214 pad 1 (the left pad in the Gerber view), and on the inner | |
40 layer where this microvia goes, one can clearly see the feature that splits the | |
41 V-DBB net coming from C214.1 into VDD-PLL and VDD-CORE branches. The lower (in | |
42 the Gerber view) branch that goes to two microvias back to the surface is | |
43 VDD-PLL, whereas the other branch that goes to an inner buried via (spanning L2 | |
44 through L5) is VDD-CORE. | |
45 | |
46 The other star routing feature in the TR-800 PCB corresponding to TI's HST203 | |
47 can be seen in the far lower right corner of the same OKPCBM~1.G1 gerber file: | |
48 look for an L shape that connects a short thin trace (going to a microvia to the | |
49 surface) to the surrounding GND copper pour. The short thin trace connected to | |
50 the GND copper pour by the L shape is what we named GND_32khz in | |
51 src/core/dbb_block.v, and the L shape on the inner layer is what eventually | |
52 became of HST203. | |
53 | |
54 The present ueda netlist source code for FC Venus is written with the | |
55 expectation that the same pseudo-component EDA trick for star routing will be | |
56 used on our board, using intnoconn feature of pcb-rnd: | |
57 | |
58 http://repo.hu/cgi-bin/pool.cgi?project=pcb-rnd&cmd=show&node=intnoconn | |
59 | |
60 There is one difference in this regard between TI's original version and ours. | |
61 In TI's original version all 3 pseudo-component objects HST201, HST202 and | |
62 HST203 were 2-way stars, with HST201 and HST202 being somehow combined in PADS | |
63 layout to form the desired 3-way star. In our version 3-way star HST200 | |
64 explicitly replaces TI's HST201+HST202 pair. The actual pcb-rnd subcircuits | |
65 for the 3-way star HST200 and the 2-way star HST203 will need to be created by | |
66 the PCB layout engineer. |