JLinkExe works, but JlinkGDBServer gives errors

carlnorum · Jun 6th 2013, 12:00am

I just got a new dev board for the part we're going to use for this project, but I can't seem to get JLinkGDBServer to connect to it. I have successfully connected, flashed, and run it using JLinkExe, but JLinkGDBServer just says:

ERROR: Could not connect to target.
Target connection failed. GDBServer will be closed...Restoring target state and closing J-Link connection...

Any suggestions for what might be different between the two that I can correct to get things working? Complete output from JLinkGDBServer is below:

$ JlinkGDBServer
SEGGER J-Link GDB Server V4.62a

JLinkARM.dll V4.62a (DLL compiled Feb 6 2013 11:45:16)

The server has been started with the following settings:
---Server related settings---
GDBInit file: none
Listening port: 2331
SWO thread listening port: 2332
Accept remote connection: yes
Logfile: off
Verify download: off
Init regs on start: on
Silent mode: off
Single run mode: off
---J-Link related settings---
J-Link script: none
Target interface: JTAG
Host interface: USB
Target endian: little
Target interface speed: 1000kHz

Connecting to J-Link...
J-Link is connected.
Firmware: J-Link V9 compiled Jan 11 2013 12:33:03
Hardware: V9.00
S/N: 59102303
Feature(s): GDB
Checking target voltage...
Listening on TCP/IP port 2331
Connecting to target...ERROR: Could not connect to target.
Target connection failed. GDBServer will be closed...Restoring target state and closing J-Link connection...
Connecting to J-Link...
J-Link is connected.
Firmware: J-Link V9 compiled Jan 11 2013 12:33:03
Hardware: V9.00
S/N: 59102303
Feature(s): GDB
Checking target voltage...
Listening on TCP/IP port 2331
Connecting to target...ERROR: Could not connect to target.
Target connection failed. GDBServer will be closed...Restoring target state and closing J-Link connection...
Shutting down...

In contrast, starting up JLinkExe works fine:

$ JLinkExe
SEGGER J-Link Commander V4.62a ('?' for help)
Compiled Feb 6 2013 11:45:20
DLL version V4.62a, compiled Feb 6 2013 11:45:16
Firmware: J-Link V9 compiled Jan 11 2013 12:33:03
Hardware: V9.00
S/N: 59102303
Feature(s): GDB
VTarget = 3.237V
Info: Could not measure total IR len. TDO is constant high.
Info: Could not measure total IR len. TDO is constant high.
No devices found on JTAG chain. Trying to find device on SWD.
Info: Found SWD-DP with ID 0x2BA01477
Info: TPIU fitted.
Info: ETM fitted.
Info: FPUnit: 6 code (BP) slots and 2 literal slots
Info: Found Cortex-M3 r2p1, Little endian.
Cortex-M3 identified.
JTAG speed: 100 kHz
J-Link>h
R0 = 00000000, R1 = A5A5A5A5, R2 = A5A5A5A5, R3 = A5A5A5A5
R4 = A5A5A5A5, R5 = 20000420, R6 = A5A5A5A5, R7 = 20001F28
R8 = A5A5A5A5, R9 = A5A5A5A5, R10= A5A5A5A5, R11= A5A5A5A5
R12= A5A5A5A5, R13= 20001F20, MSP= 20007FE0, PSP= 20001F20
R14(LR) = 00003617, R15(PC) = 00003606
XPSR = 61000000, APSR = 60000000, EPSR = 01000000, IPSR = 00000000
CFBP = 02000000, CONTROL = 02, FAULTMASK = 00, BASEPRI = 00, PRIMASK = 00
CycleCnt = 00000000
J-Link>r
Reset delay: 0 ms
Reset type NORMAL: Resets core & peripherals via SYSRESETREQ & VECTRESET bit.
J-Link>g
J-Link>

carlnorum · Jun 6th 2013, 12:05am

I should note, I tried some obvious things like changing the -speed setting for JLinkGDBServer, adding a -device flag, etc.

carlnorum · Jun 6th 2013, 1:14am

I was playing around some more, and:

JlinkGDBServer -if SWD

worked. I don't know what changed, but I didn't need to do that for the previous part (though it's very similar). Anyway, problem solved. Thanks!

SEGGER - Alex · Jun 7th 2013, 5:03pm

Hi,

Short explanation:
For Cortex-M there are in general two debug interfaces available:
JTAG (5 signals: TCK, TMS, TDI, TDO, TRST)
SWD (2 Signals: SWCLK, SWDIO)

J-Link Commander tries to find anything on all interfaces supported by the connected J-Link by default.
This is somewhat historical and not really the best way to proceed, since communicating on an interface that the target does not support may confuse it.
The idea is, to tell J-Link what interface to search on.
In your case, it seems that only the signals for SWD are connected and so only a connection via SWD can be established, so you need to tell GDBServer to use SWD as interface. Default is JTAG.

Best regards
Alex

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