# OpenOCD and FTDI Chips To let OpenOCD correctly drive the FTDI chip, we need to tell OpenOCD the hardware configuration of the FTDI chip through the config file: ```properties ### FTDI interface configuration ### ftdi_vid_pid 0x0403 0x6010 ftdi_channel 0 ftdi_layout_init 0x0888 0x8B8B ``` Reference: We will analyze the config file line by line ```properties ftdi_vid_pid 0x0403 0x6010 ``` This line tells OpenOCD to find the USB device with the signature of corresponding vendor ID (VID) and product ID (PID). 0x0403: [Future Technology Devices International Limited](https://the-sz.com/products/usbid/index.php?v=0x0403) 0x6010: FT2232C/D/H Dual UART/FIFO IC ```properties ftdi_channel 0 ``` Selects the channel of the FTDI device to use for MPSSE operations. Here we select channel A, which is the first channel (channel 0). ```properties ftdi_layout_init 0x0800 0x0800 ``` Defines the initial data and IO direction of the GPIOs. The mapping is as follows: | 0x | bit \[15..8] | bit \[7..0] | | -- | ------------ | ------------ | | | ACBUS\[7..0] | ADBUS\[7..0] | As an simple example, to initialize the JTAG LED on FT-LINK, which is an open-drain LED connected to ACBUS3 pin, we use the following setting ```properties ftdi_layout_init 0x0800 0x0800 # this initialize LED off ``` ```properties ftdi_layout_init 0x0000 0x0800 # this initialize LED on ``` We can also define the JTAG\_LED variable with the following command ```properties ftdi_layout_signal JTAG_LED -oe 0x0800 ``` Then, in the init routine, we can use the variable to reference this pin and blink the LED ```properties init ftdi_set_signal JTAG_LED 0 # LED on sleep 1000 ftdi_set_signal JTAG_LED z # LED off sleep 1000 ftdi_set_signal JTAG_LED 0 # LED on ``` note that since we are only enabling the output driver by the `-oe` flag, the chip can only drive it open-drain, and therefore we are only allow to set the signal state to either low (`0`) or high-Z (`z`). If we try to set it to high (`1`), we will get the following error: ```bash Error: interface can't drive 'JTAG_LED' high ``` If we have some normal signal that we want to drive both high and low, we can use the `-data` flag instead: ```properties ftdi_layout_signal JTAG_LED -data 0x0800 ``` ```properties init ftdi_set_signal JTAG_LED 0 # LED on sleep 1000 ftdi_set_signal JTAG_LED 1 # LED off sleep 1000 ftdi_set_signal JTAG_LED 0 # LED on ``` If we somehow want all the states, we do the following ```properties ftdi_layout_signal JTAG_LED -data 0x0800 -oe 0x0800 ```