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====== Bitbang-JTAG: universal homebrew USB-programmer ======
Chip [[http://ftdichip.com/Products/FT232R.htm | FTDI FT232R]] has a special mode named "synchronous bit bang". It could be used for implementing fast serial interfaces like SPI or JTAG. Bitbang mode is described in application note {{http://ftdichip.com/Documents/AppNotes/AN232R-01_FT232RBitBangModes.pdf | "Bit Bang Modes for the FT232R and FT245R"}}.

There exist several starter boards based on FT232R, for example [[http://chip-dip.ru/product0/9000043502.aspx | MMUSB232RL]]
or [[http://www.sparkfun.com/commerce/product_info.php?products_id=718 | FT232RL Breakout]].

{{mmusb232rl.jpg}}{{ft232rl-breakout.jpg}}

Using these boards, one could easily build a simple JTAG programmer, for example:

{{prog-mcusb-sch.png}}

Example of openocd.cfg for Olimex SAM7-EX256 board:
<code>
# Daemon configuration
#~~~~~~~~~~~~~~~~~~~~~
telnet_port 2001
gdb_port 2000

# Interface
#~~~~~~~~~~
# We use homebrew usbjtag-compatible schematics
# based on FT232R Breakout board from SparkFun.com.
interface ft232r
ft232r_device_desc "FT232R USB UART"
ft232r_vid_pid 0x0403 0x6001

# Target configuration
#~~~~~~~~~~~~~~~~~~~~~
source [find target/sam7x256.cfg]
</code>

Patch for OpenOCD: debugger is available here: {{openocd-ft232r.pch.gz}}.