[Libre-soc-bugs] [Bug 517] Define JTAG pins and set up with litex for ulx3s85f

[bugzilla-daemon at libre-soc.org]

https://bugs.libre-soc.org/show_bug.cgi?id=517

--- Comment #96 from Cole Poirier <colepoirier at gmail.com> ---
(In reply to Luke Kenneth Casson Leighton from comment #95)
> http://openocd.org/doc/html/Debug-Adapter-Configuration.html#index-ftdi

``` from above link
List of connections (default physical pin numbers for FT232R in 28-pin SSOP
package):

    - RXD(5) - TDI
    - TXD(1) - TCK
    - RTS(3) - TDO
    - CTS(11) - TMS
    - DTR(2) - TRST
    - DCD(10) - SRST 
```

``` from
https://github.com/ntfreak/openocd/blob/master/src/jtag/drivers/ft232r.c#L79-L99
/**
 * FT232R GPIO bit number to RS232 name
 */
#define FT232R_BIT_COUNT 8
static char *ft232r_bit_name_array[FT232R_BIT_COUNT] = {
        "TXD", /* 0: pin 1  TCK output */
        "RXD", /* 1: pin 5  TDI output */
        "RTS", /* 2: pin 3  TDO input */
        "CTS", /* 3: pin 11 TMS output */
        "DTR", /* 4: pin 2  /TRST output */
        "DSR", /* 5: pin 9  unused */
        "DCD", /* 6: pin 10 /SYSRST output */
        "RI"   /* 7: pin 6  unused */
};

static int tck_gpio; /* initialized to 0 by default */
static int tdi_gpio = 1;
static int tdo_gpio = 2;
static int tms_gpio = 3;
static int ntrst_gpio = 4;
static int nsysrst_gpio = 6;
```

```from ft232 usb to 6 pin female header manual
 _________________________
| Pin # | Name |  Colour  |
|-------|------|----------|
|   1   | GND  |  Black   |
|   2   | CTS  |  Brown   |
|   3   | VCC  |  Red     |
|   4   | TXD  |  Orange  |
|   5   | RXD  |  Yellow  |
|   6   | RTS  |  Green   |
|_______|______|__________|
```

``` ft232 pin and wire colour table converted to jtag signal names
 _________________________
| Pin # | Name |  Colour  |
|-------|------|----------|
|   1   | GND  |  Black   |
|   2   | TMS  |  Brown   |
|   3   | VCC  |  Red     |
|   4   | TCK  |  Orange  |
|   5   | TDI  |  Yellow  |
|   6   | TDO  |  Green   |
|_______|______|__________|
```

Luke, my proposal is to change the wire colours of on the wiki specified for
the fpga to the colours present on the ft232 6 pin female header.

Is it a problem that the f232r.c openocd file specifies trst and srst but not
gnd and vcc? Or are gnd and vcc not specified in the openocd interface 'c' file
because they are electrical and managed by power hardware on the ft232 chip?

Any other concerns about this migration? Or once I put this on the ECP5_FPGA
wiki page under a header titled 'jtag over ft232' will we be good to proceed
with connecting the wires to the fpga and trying to get the jtag tap of
libre-soc recognized? - after the wiring is triple checked of course.

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