Add support for GR-CITRUS

[kkitayam]

Describe the PR

Add support for GR-CITRUS as a USB device. A distributer for the board is corestaff, and the site is corestaff online.

Additional context

This PR needs following tools.

• GCC for Renesas 8.3.0.202004-GNURX
• in-circuit programmer
  In order to download a firmware, it needs at least one of the following.
  • SEGGER JLink
    JLink can download a firmware via JTAG interface. But, GR-CITRUS needs to solder some pads to enable JTAG interface. Let me explain details later.
  • Renesas Flash Programmer
    In this application, it needs to short JP1(MD) of GR-CITRUS and execute USB boot mode only when operating.

I have confirmed that all examples for device are built by Windows 10. And looks like follow examples work fine:
board_test, cdc_dual_ports, cdc_msc, cdc_msc_freertos, hid_generic_inout, msc_dual_lum, net_lwip_webserver and webusb_serial.
I have not confirmed some examples for HID input operation since GR-CITRUS has no general purpose button.
audio_test and uac2_headset do work, but I'm not sure if this is the expected behavior.

How to connect JLink and GR-CITRUS

• Short the following pads individually with solder.
  • J4
  • J5
• Short EMLE pad and 3.3V(GR-CITRUS pin name) with a wire.

The pads are the back side of GR-CITRUS.

Connet the pins between GR-CITRUS and JLink as follows.

JTAG Function	GR-CITRUS pin name	JLink pin No.	note
VTref	3.3V	1
TRST	5	3
GND	GND	4
TDI	3	5
TMS	2	7
TCK	14	9	short J4
TDO	9	13	short J5
nRES	RST	15

JLink firmware needs to update to V6.96 or newer version to avoid a bug regarding downloading.

When using SEGGER RTT, I recommend to add RX_NEWLIB=0 option to make command arguments.
The option is used to change the C runtime library to optlib from newlib.
In my experience, RTT does not work with newlib.

[hathach]

Superb ! brilliant works, thank you very much for your PR. Too bad that it seems like renesas boards is hard to find and very expensive as well. Therefore I couldn't perform any hand-on tests any will merge this as it is. Which looks really good, except for

1. maybe move the submodule from renesas to renesas/rx63 to allow as more families later on
2. I wonder if rx63n freertos start scheduler would return at all ?

once the submouldes is moved, I could help to fix the ci.

[hathach]

Thank you very much for your detail instruction of board usage. Too bad, I couldn't find it in local/online store. Since there is a bit of extra works with the board. It would be better to put this summary work into the gr_citrus.c as comment, it would probably help us in the future.

[hathach]

@kkitayam I have fixed the ci issue caused by lacking the gnurx toolchain. Since rx63n has its own toolchain, it is best to move it into a family (with gr_citrus as the only board). This is done by simply add the family.mk that include the board.mk. The build command is exactly the same as before make BOARD=gr_citrus.

This allow us to run a separate ci job that cached the gnurx toolchain for rx63n family only. This is already pushed toward your branch, please fetch/pull first before making additional changes if any.

[hathach]

Excellent ! It is perfect now, thank you very much for your effort. Great PR as usual, I am happy that we could get the first family from renesas ported 👍 👍