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Mar 19, 2009, 02:00 PM
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4 megabit point 2 point soldering 4 U


So U want more bandwidth but U don't have enough memory for ping pong buffers. U need smaller audio buffers but Linux has too much latency. U want to send different streams of data without having to multiplex packets by hand. U need USB endpoints.

The pros don't call blocking read calls on a file handle like U do with UARTs. For USB they allocate many file handles & request simultaneous I/O on all of them in the background. That way the device always has virtual buffers to fill & doesn't overflow waiting for Linux. Also, each endpoint can be a different stream, so U don't need to multiplex anything by hand. It's a great way to stream telemetry.

With that out of the way, VicaCopter shows up like this in /proc/bus/usb/devices.

T: Bus=02 Lev=02 Prnt=20 Port=01 Cnt=02 Dev#= 34 Spd=12 MxCh= 0
D: Ver= 2.00 Cls=00(>ifc ) Sub=00 Prot=00 MxPS= 8 #Cfgs= 1
P: Vendor=04d8 ProdID=000b Rev= 0.01
C:* #Ifs= 1 Cfg#= 1 Atr=80 MxPwr=100mA
I: If#= 0 Alt= 0 #EPs= 8 Cls=00(>ifc ) Sub=00 Prot=00 Driver=(none)
E: Ad=01(O) Atr=02(Bulk) MxPS= 32 Ivl=0ms
E: Ad=81(I) Atr=02(Bulk) MxPS= 64 Ivl=0ms
E: Ad=02(O) Atr=02(Bulk) MxPS= 64 Ivl=0ms
E: Ad=82(I) Atr=02(Bulk) MxPS= 64 Ivl=0ms
E: Ad=03(O) Atr=02(Bulk) MxPS= 64 Ivl=0ms
E: Ad=83(I) Atr=02(Bulk) MxPS= 64 Ivl=0ms
E: Ad=04(O) Atr=02(Bulk) MxPS= 32 Ivl=0ms
E: Ad=84(I) Atr=02(Bulk) MxPS= 32 Ivl=0ms

That's a lot of endpoints. There's 2 for sonar, 1 for the Xbee, 1 for 72Mhz, 1 for commands, & some fillers to make the code legible. So how fast can the PIC spit out data if it isn't sampling audio? 4 megabits. 2x faster than 3G cell phones, 20x faster than your day job, 1/2 as fast as Comca$t, 46x faster than Xbee.

In a short time, expect those Ardu dillo nova dova's to really support USB instead of convert it to a UART.

Unfortunately, the ADC still runs out of clockcycles above 157khz. The optoisolator suxs. The resistance decreases when the sound is loud & increases when the sound is quiet. It's not a linear resistor, as the Goog said.

So what about PWM on the Vref pins? It blew up in the last attempt. Mainly, the delta Vref can only go to 3V. There must be some cheap Chinese gadget which can do the job.

https://www.rcgroups.com/forums/showthread.php?t=969538
Last edited by Jack Crossfire; Mar 19, 2009 at 07:44 PM.
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