diff options
| -rw-r--r-- | src/jtag/drivers/ft2232.c | 24 |
1 files changed, 18 insertions, 6 deletions
diff --git a/src/jtag/drivers/ft2232.c b/src/jtag/drivers/ft2232.c index b45e8a4d..8e835c59 100644 --- a/src/jtag/drivers/ft2232.c +++ b/src/jtag/drivers/ft2232.c @@ -32,12 +32,24 @@ * JTAG adapters based on the FT2232 full and high speed USB parts are * popular low cost JTAG debug solutions. Many FT2232 based JTAG adapters * are discrete, but development boards may integrate them as alternatives - * to more capable (and expensive) third party JTAG pods. Since JTAG uses - * only one of the two ports on these devices, on integrated boards the - * second port often serves as a USB-to-serial adapter for the target's - * console UART even when the JTAG port is not in use. (Systems which - * support ARM's SWD in addition to JTAG, or instead of it, may use that - * second port for reading SWV trace data.) + * to more capable (and expensive) third party JTAG pods. + * + * JTAG uses only one of the two communications channels ("MPSSE engines") + * on these devices. Adapters based on FT4232 parts have four ports/channels + * (A/B/C/D), instead of just two (A/B). + * + * Especially on development boards integrating one of these chips (as + * opposed to discrete pods/dongles), the additional channels can be used + * for a variety of purposes, but OpenOCD only uses one channel at a time. + * + * - As a USB-to-serial adapter for the target's console UART ... + * which may be able to support ROM boot loaders that load initial + * firmware images to flash (or SRAM). + * + * - On systems which support ARM's SWD in addition to JTAG, or instead + * of it, that second port can be used for reading SWV/SWO trace data. + * + * - Additional JTAG links, e.g. to a CPLD or * FPGA. * * FT2232 based JTAG adapters are "dumb" not "smart", because most JTAG * request/response interactions involve round trips over the USB link. |