Hello FreeCalypso community, Knowing that some people have been using Sysmocom mv-uart adapters with our FCDEV3B boards instead of our officially recommended FT2232D adapter, I have recently bought one of those little mv-uart boards from Sysmocom webshop for evaluation testing, and I have just completed my experiments with it. Based on the results of my testing, the only recommendation I can make is that FreeCalypso users should NOT use mv-uart adapters with FreeCalypso boards - until our DUART28 adapter becomes available (see below), you should use FT2232D adapters such as these:
http://pldkit.com/other/ft2232d-module Besides the obvious drawback of CP2105 having poor support for non-standard high baud rates like 812500 bps (CP2105 supports them on only one channel, whereas FT2232x support them on both channels), mv-uart has been found to perform much worse in terms of partial power-down scenarios as detailed below. Partial power-down scenario 1: you connect battery-emulating power to your FCDEV3B (orange power input connector), UART lines are connected between your FCDEV3B and your USB to dual UART adapter, the latter adapter has USB power present (ttyUSBx devices appear on your Linux host), but you haven't pressed PWON or RESET on your FCDEV3B yet - perhaps you need to run a tool such as fc-loadtool and then press PWON. With FT2232D adapters the current flowing from the powered-on USB adapter into the powered-down Calypso target is about 1.7 mA per UART line, which is not ideal but certainly quite tolerable. But with mv-uart this current has been measured to be as high as 8 mA with the voltage selection switch set to 2.8V, or almost 12 mA with the switch set to 3.3V - yikes! (The difference must be due to CP2105 having stronger output drivers than FT2232D.) Partial power-down scenario 2: the Calypso device is fully powered on and running (green LED lit on FCDEV3B), UART lines are connected between FCDEV3B and USB UART adapter boards, but there is no USB host present - the USB adapter board has no power. Both currently available options (raw FT2232D adapters and mv-uart) perform badly under this scenario, with significant current flowing from Calypso output cells into the powered-down USB board, but mv-uart is worse: with FT2232D this current has been measured to be about 6 mA per UART line, but with mv-uart it is somewhere between 10 and 11 mA per UART line. This partial power-down scenario can be easily avoided on FCDEV3B (simply don't do it), but we have another FreeCalypso development board coming down the pike (another 2-3 months maybe) that will feature an LCD and a keypad, allowing untethered phone operation - and then this scenario will begin to matter a lot more. Thus the current official advice is to use PLDkit FT2232D adapters and not mv-uart. But the raw FT2232x option (whether from PLDkit or other vendors) is not perfect either: it still performs rather badly in partial power-down scenario 2, and it puts out 3.3V rather than Calypso-native 2.8V. I've been wanting it for the past few years now, ever since we launched FCDEV3B in 2017, but over the past couple of months I finally bit the bullet and designed my own FreeCalypso- specific USB to dual UART adapter, called DUART28. DUART28 PCBs just arrived from China yesterday, I will be taking them to my assembly shop in the next few days, and then we'll see how long it takes them to turn around. Our new DUART28 adapter is based around the same FT2232D chip as our current PLDkit adapters (sorry Sysmocom folks, I *really* dislike your CP2105), but this FreeCalypso-specific adapter principally differs from a generic FT2232D like PLDkit as follows: * As reflected in the name, DUART28 will put out 2.8V UART signals (native for Calypso) instead of 3.3V. This feat is achieved by inserting a 74LVC541A buffer after FT2232D outputs, powered by an on-board 2.8V LDO regulator. * Another 74LVC541A buffer is inserted in the other direction, between Calypso outputs and FT2232D inputs. This buffer is expected to fix partial power-down scenario 2: LVC buffers are specifically designed for partial power-down applications and have a datasheet-guaranteed low Ioff in the uA range. Assuming that these new DUART28 adapters will work as designed when I get them assembled, they will become the new standard accessory to be supplied with FCDEV3B and future FC development boards. Anyone who already has an FCDEV3B will be able to get the new DUART28 adapter as well. Hopefully we'll have them in another few weeks... Hasta la Victoria, Siempre, Mychaela aka The Mother _______________________________________________ Community mailing list [email protected] https://www.freecalypso.org/mailman/listinfo/community
