--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/eeproms/jtag-unbuf	Sun Sep 03 18:24:27 2023 +0000
@@ -0,0 +1,30 @@
+# This EEPROM configuration is meant to be programmed into COTS FT2232D
+# breakout boards used as unbuffered JTAG adapters.  The custom USB VID:PID
+# belongs to Falconia Partners LLC; we hereby allow the community to program
+# this PID into generic FT2232D boards (not made by Falconia) as long as
+# it is used for the present purpose with this full EEPROM configuration.
+#
+# The purpose of having a custom USB ID is to prevent the Linux kernel
+# ftdi_sio driver from treating this FT2232D instance as a dual UART and
+# creating a ttyUSB device for Channel A.  If you wish to use Channel B
+# as a UART (which is still available for that purpose), you will need to use
+# a Linux kernel version with commit 6cf87e5edd9944e1d3b6efd966ea401effc304ee
+# included, or apply that commit locally if your kernel version does not
+# include it.
+
+vid 0x0403	# FTDI
+pid 0x7151	# Allocated by FTDI to Falconia Partners LLC
+manuf FTDI
+product Unbuffered JTAG adapter
+
+# We program Channel A to come up in the 245 FIFO mode prior to being
+# switched into MPSSE mode by OpenOCD, as opposed to the default 232 UART mode.
+# If the FT2232D chip's ADBUS pins are connected directly to the JTAG target
+# without a buffer (what we mean by an unbuffered JTAG adapter), the default
+# 232 UART mode is NOT safe, as it will produce a fight on the ADBUS2 line
+# between the UART RTS output and the target's TDO output.  245 FIFO mode is
+# expected to be safer, as all 8 ADBUS lines will be inputs for as long as
+# the ACBUS2 line is left unconnected and not driven by anything.
+
+byte00	0x01	# Channel A: FIFO mode, D2XX driver
+byte01	0x08	# Channel B: UART mode, VCP driver