FreeCalypso > hg > freecalypso-schem2
view venus/doc/Star-points-in-core @ 92:148fab6e07e3
add RTC domain test points
author | Mychaela Falconia <falcon@freecalypso.org> |
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date | Sat, 11 Dec 2021 04:48:30 +0000 |
parents | 971c05950675 |
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iWOW's TR-800 module, whose reverse-engineered PCB layout will serve as a reference for the Calypso core of FC Venus, is nothing but a mass-produced version of TI's Leonardo reference design. We don't have any original PCB layout files for Leonardo, but we do have schematics, in 3 different versions: ftp://ftp.freecalypso.org/pub/GSM/Calypso/Leonardo_plus_RD122.pdf ftp://ftp.freecalypso.org/pub/GSM/Calypso/Leonardo_plus_quadband_schem.pdf ftp://ftp.freecalypso.org/pub/GSM/Calypso/Leonardo_rev05.pdf TR-800 is based on quadband Leonardo+ (that's what makes it interesting), but the hobbled 2-band version of Leonardo is the only one for which we have TI's original DSN (OrCAD) schematic file, in addition to the corresponding PDF: ftp://ftp.freecalypso.org/pub/GSM/Calypso/Leonardo_rev05.dsn TI's group in Aalborg (Denmark) that designed and built their development boards used OrCAD for schematics and PADS for PCB layout. We have their PADS PCB design file for a different board from about the same time frame (E-Sample), but not for any Leonardo variant. If you look at the baseband page of Leonardo schematics (this part is the same in all 3 versions), you will see 3 symbols denoting star routing: HST201 and HST202 (labeled "STAR_CONFIG") split V-DBB net into VDD-PLL and VDD-CORE branches, and HST203 (labeled "GND_POINT") creates a special ground for the 32.768 kHz oscillator circuit, connected to the rest of board ground at just one point. This star routing in TI's reference version of Calypso/Leonardo core exists not only in TI's schematics, but also in the physical PCB layout which we have recovered from TR-800 by reverse engineering. If you look at the Gerber files which we received from the PCB RE company (published on our FTP site in 2021), specifically the OKPCBM~1.G1 gerber file corresponding to the inner layer just below the surface (L2 or L5 depending on which way you count), you can see the physical features that were once produced, presumably in PADS, to effect the star routing depicted in the schematics. The physical PCB star routing feature corresponding to HST201 & HST202 resides just underneath C214 footprint. There is a microvia (blind via going only one layer in) inside C214 pad 1 (the left pad in the Gerber view), and on the inner layer where this microvia goes, one can clearly see the feature that splits the V-DBB net coming from C214.1 into VDD-PLL and VDD-CORE branches. The lower (in the Gerber view) branch that goes to two microvias back to the surface is VDD-PLL, whereas the other branch that goes to an inner buried via (spanning L2 through L5) is VDD-CORE. The other star routing feature in the TR-800 PCB corresponding to TI's HST203 can be seen in the far lower right corner of the same OKPCBM~1.G1 gerber file: look for an L shape that connects a short thin trace (going to a microvia to the surface) to the surrounding GND copper pour. The short thin trace connected to the GND copper pour by the L shape is what we named GND_32khz in src/core/dbb_block.v, and the L shape on the inner layer is what eventually became of HST203. The present ueda netlist source code for FC Venus is written with the expectation that the same pseudo-component EDA trick for star routing will be used on our board, using intnoconn feature of pcb-rnd: http://repo.hu/cgi-bin/pool.cgi?project=pcb-rnd&cmd=show&node=intnoconn There is one difference in this regard between TI's original version and ours. In TI's original version all 3 pseudo-component objects HST201, HST202 and HST203 were 2-way stars, with HST201 and HST202 being somehow combined in PADS layout to form the desired 3-way star. In our version 3-way star HST200 explicitly replaces TI's HST201+HST202 pair. The actual pcb-rnd subcircuits for the 3-way star HST200 and the 2-way star HST203 will need to be created by the PCB layout engineer.