JTAG on Rock64

[tdundon]

I see that the rk3328 offers the TCK and TMS pins for JTAG (at the expense of using the SD card).  But I don't see any pins for TDI or TDO.  On the other hand, the rk3328 development board apparently supports JTAG.  Does someone have a schematic for hooking up JTAG to the Rock64?

Thanks,
Tom

[xalius]

Hi, are you planning on debugging bare metal A53 applications, or low level firmware stuff? I don't see the rest of the JTAG pins in the pinmux tables either, and when further reading the RK3328 user manual it seems it's not really JTAG but SWDIO they support with JTAG emulated by the DAP SWJ-DP IP block, which is indeed only a two pin interface described in chapter 11...

[tdundon]

Hi, are you planning on debugging bare metal A53 applications, or low level firmware stuff? I don't see the rest of the JTAG pins in the pinmux tables either, and when further reading the RK3328 user manual it seems it's not really JTAG but SWDIO they support with JTAG emulated by the DAP SWJ-DP IP block, which is indeed only a two pin interface described in chapter 11...

Hi Xalius,
I always end up needing JTAG to fix those intermittent, timing-related, bugs.     In looking at the RK3328 TRM I also saw the reference to the CoreSight DAP (Debug Access Port) module that is part of the RK3328.  As you say, it supports both SWD (Serial Wire Debug) and JTAG, but the RK3328 might not expose the extra JTAG pins.  I'm becoming a little suspicious of the claim that the RK3328 dev board supports JTAG.  I may ask RockChip if this is just a cut-and-paste error from documentation of another SoC.

I have a Lauterbach so JTAG would be convenient, but I saw that Segger offers a JTAG/SWD product that looks like it would do the same thing.  I'm just not familiar with the SWD interface.  I guess it can't be too different.  If you have further insights please let me know.

Thanks,
Tom

Update: It looks like the Segger J-Link DOES NOT support the Cortex A53. They apparently plan to but only on the Ultra+ model (which is out my price range).

[xalius]

In my experience JTAG/SWD is pretty useless when used with operating systems or firmware that uses virtual memory and multiple cores/processes/threads? There are more advanced debug systems which are often embedded in those SoC to do OS level hardware debugging, but JTAG might still be useful if you want to work on bootloader stuff or bare metal applications...

PS: JTAG via sdcard-pins seems to be pretty common because of tablets and phones, Allwinner SoC have that as well and often you can use an adapter like this:

https://www.cubietruck.com/products/usd-breakout-board