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Subject: how to achieve continuous transfers with ft2232h and libftdi

From: Steffen Mauch <steffen.mauch@xxxxxxxxx>
To: libftdi@xxxxxxxxxxxxxxxxxxxxxxx
Date: Sun, 31 Jan 2010 12:51:17 +0100

I use the FT2232H with MPSSE for SPI transfer.
Connected to the SPI bus is a Analog Digital converter which also has an SPI interface.

The ADC is able to transfer 125000 * 3 Bytes per channel. It has 8 channels. The FT2232H could transfer up to 30 Mbit and there shouldn't be any problems with the bandwidth.

I am not so familiar with the usb protocol :-/ so what is the best way to achieve a continuous reading. I mean, if I read 4096 bytes for example then I want to read another 4096 bytes just after recieving the "old" 4096 bytes.
If there is not much space between this action, I could read everything.
I know that this could only work, if nothing else is connected to this usb host, because otherwise some other peripherial could be active. Then I have to wait and I don't have a continuous measurement.

My idea was to set with ftdi_set_latency_timer(&ftdic, xxx) the latency to for example 2ms and calculate with the clock of spi how much I should read in 2ms.

Is this possible or won't it work?
Or is there another (maybe better) possibility how to achieve my goal?


Mit freundlichen Grüßen
Steffen Mauch

cand. B.Sc. Steffen Mauch

Digital Communications & Signal Processing Lab
Fakultät Computer & Electrical Engineering

Hochschule Furtwangen University
Robert-Gerwig-Platz 1
78120 Furtwangen

Tel    +49 (0)7723 920 2342
Fax    +49 (0)7723 920 2802
Cell   +49 (0)1511 235 2355


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