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stlink: remove reset pulse when entering in JTAG 

Until version J14 the behaviour of ST-Link was to send a reset
pulse to the target when the debug connection is started in JTAG
mode. No reset pulse is sent, instead, in SWD mode.
Version J15 introduces a new parameter to avoid the reset pulse in
JTAG mode, aligning the behaviour with SWD.

This reset from the ST-Link, if propagated to the target, prevents
attaching a running target.

Actually this reset pulse is very short (few microsecond) and can
be easily filtered out by an on-board capacitor, usually present
on the reset wire (mainly to filter the bounces of the reset
button). Moreover, most of the use cases for ST-Link are with SWD
(not with JTAG) and this has probably further masked this JTAG
specific behaviour.

OpenOCD can tolerate it but requires the flag "connect_assert_srst"
to the command "reset_config", but the flag is not present in any
configurations in folder tcl. This enforces the guess it was not
noticed due to on-board capacitors or missing connection of reset
pin or ST-Link only used in SWD; so it's safe applying this patch.

Change the default behaviour to avoid reset in JTAG at connection.
There is no need to manage the ST-Link version here, since every
parameter that is not recognized by older ST-Link is treated as
"connect in JTAG with reset pulse", keeping backward compatibility.

Change-Id: Idc97a1457279e3970fd0839cadbff22d9b0302d4
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: http://openocd.zylin.com/4713
Tested-by: jenkins
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>
This commit is contained in:
Antonio Borneo 2018-09-24 15:26:40 +02:00 committed by Spencer Oliver
parent 80ce68b42c
commit 717d3af087
1 changed files with 5 additions and 5 deletions
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10
src/jtag/drivers/stlink_usb.c
View File

@ -205,7 +205,6 @@ struct stlink_usb_handle_s {
#define STLINK_SWIM_READMEM 0x0b
#define STLINK_SWIM_READBUF 0x0c
#define STLINK_DEBUG_ENTER_JTAG 0x00
#define STLINK_DEBUG_GETSTATUS 0x01
#define STLINK_DEBUG_FORCEDEBUG 0x02
#define STLINK_DEBUG_APIV1_RESETSYS 0x03
@ -223,8 +222,9 @@ struct stlink_usb_handle_s {
#define STLINK_DEBUG_APIV1_WRITEDEBUGREG 0x0f
#define STLINK_DEBUG_APIV1_SETWATCHPOINT 0x10
#define STLINK_DEBUG_ENTER_JTAG 0x00
#define STLINK_DEBUG_ENTER_SWD 0xa3
#define STLINK_DEBUG_ENTER_JTAG_RESET 0x00
#define STLINK_DEBUG_ENTER_SWD_NO_RESET 0xa3
#define STLINK_DEBUG_ENTER_JTAG_NO_RESET 0xa4
#define STLINK_DEBUG_APIV1_ENTER 0x20
#define STLINK_DEBUG_EXIT 0x21
@ -830,7 +830,7 @@ static int stlink_usb_mode_enter(void *handle, enum stlink_mode type)
h->cmdbuf[h->cmdidx++] = STLINK_DEBUG_APIV1_ENTER;
else
h->cmdbuf[h->cmdidx++] = STLINK_DEBUG_APIV2_ENTER;
h->cmdbuf[h->cmdidx++] = STLINK_DEBUG_ENTER_JTAG;
h->cmdbuf[h->cmdidx++] = STLINK_DEBUG_ENTER_JTAG_NO_RESET;
break;
case STLINK_MODE_DEBUG_SWD:
h->cmdbuf[h->cmdidx++] = STLINK_DEBUG_COMMAND;
@ -838,7 +838,7 @@ static int stlink_usb_mode_enter(void *handle, enum stlink_mode type)
h->cmdbuf[h->cmdidx++] = STLINK_DEBUG_APIV1_ENTER;
else
h->cmdbuf[h->cmdidx++] = STLINK_DEBUG_APIV2_ENTER;
h->cmdbuf[h->cmdidx++] = STLINK_DEBUG_ENTER_SWD;
h->cmdbuf[h->cmdidx++] = STLINK_DEBUG_ENTER_SWD_NO_RESET;
break;
case STLINK_MODE_DEBUG_SWIM:
h->cmdbuf[h->cmdidx++] = STLINK_SWIM_COMMAND;