Replace CP2105 with FT4232H
I'd like to suggest that for new SB version CP2105 USB-UART should be replaced with 4-channel FT4232H and the whole connection tree made very similar to DIOT KU FMC Carrier:
- channel A - JTAG (will work as Vivado dongle after EEPROM configuration, done already for FMC Carrier)
- channel B - I2C (with access at least to EEPROM with MAC address)
- channel C - PS UART
- channel D - PL UART
The idea behind I2C is to make life easier for technicians and support personnel. There should be an easy way to read out the MAC address without the need to power up and start Zynq PS.
TBD if/what other ICs could be accessed this way.
PS_SRST_B connection
Digilent and Xilinx on-board JTAG interfaces have (optional) JTAG SRST_B signal connected.
Although JTAG specification says this signal is optional, it seems to be necessary, or at least recommended, for Zynq PS debugging - see:
Xilinx forums and Sinara Github discussions.
On all the boards/dongles that I could have a look at schematics, this signal is always connected to FTDI port A, GPIO 7.
I'd recommend wiring it up like this on SB as well but with a 0R resistor.
The reason for that is that I don't know if this will work properly with a custom EEPROM config, so we need to have a backup solution in case SRST_B creates problems.