[lowrisc-dev] KC705 support

Dr Jonathan Kimmitt jrrk2 at cam.ac.uk
Tue Aug 22 11:29:15 BST 2017

The KC705 .xdc file mentions two signals

set_property PACKAGE_PIN M19 [get_ports USB_TX]
set_property IOSTANDARD LVCMOS25 [get_ports USB_TX]
set_property PACKAGE_PIN K23 [get_ports USB_RTS]
set_property IOSTANDARD LVCMOS25 [get_ports USB_RTS]
set_property PACKAGE_PIN K24 [get_ports USB_RX]
set_property IOSTANDARD LVCMOS25 [get_ports USB_RX]
set_property PACKAGE_PIN L27 [get_ports USB_CTS]
set_property IOSTANDARD LVCMOS25 [get_ports USB_CTS]

You will note that the sense is the opposite of what a rational person 
would do
(i.e. it refers to the PC side). This may mean you need to reverse the 
sense of
CTS and RTS. Referring to the circuit diagram from the Xilinx website 
might help here.

Also the SD interface needs a reset. I have tentatively connected this to

set_property PACKAGE_PIN Y21 [get_ports sd_reset]
set_property IOSTANDARD LVCMOS25 [get_ports sd_reset]

but in the Xilinx .xdc file, this is identified as SDIO_SDWP

The SD/MMC card specification history has a long history of changing 
names, so this also
needs careful review.

Getting these pins to actually work in hardware is another matter as 
Stefan points out.


On 22/08/17 11:16, Stefan Wallentowitz wrote:
> On 22.08.2017 12:04, Wei Song wrote:
>> The 'rts' and 'cts' signals are used for UART hardware flow control
>> which is used to support the high baud rate.
>> Actually I am not the most knowledgable person on this matter.
>> On our mail list, Jonathan and Stefan have already started to provide
>> information regarding UART.
>> Stefan is the original author for this high speed UART interface, which
>> amazed me initially as well.
> Hi Armia,
> the UART chip on the KC705 is a joke. As you correctly observed, it only
> supports 1MBaud. But beyond that it doesn't have hardware flow control,
> which the current implementation needs. Anyhow, for testing and ramping
> up that should be okay, but for traces it may become an issue. There is
> the plan to add XON/XOFF flow control this winter, that will be helpful
> then.
> As I said the only setup we currently support is the Cypress Superspeed
> (USB 3.0) FMC board. We use it on the VCU108 in another project but with
> the same debug interface and it works like a charm. I also have a FT300
> FMC board here, but again won't find time before October/November to get
> it running.
> If anyone of you would like to work on it instead, I am happy to assist.
> Cheers,
> Stefan

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