Skip to content

Feature: implementation of jtagtap_cycle for JLink backend #2182

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
ALTracer wants to merge 2 commits into
base: main
Choose a base branch
from
Open

Feature: implementation of jtagtap_cycle for JLink backend #2182

Changes from all commits
Commits
Show all changes
2 commits
Select commit Hold shift + click to select a range
bb822f2
hosted/jlink: Use jtagtap_cycle to switch from SWD to JTAG
ALTracer Jan 29, 2026
d8a5c4d
hosted/jlink: Implement jtagtap_cycle via jlink_transfer
ALTracer Jan 29, 2026
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
22 changes: 17 additions & 5 deletions src/platforms/hosted/jlink_jtag.c
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -42,8 +42,6 @@ static void jlink_jtag_tdi_seq(bool final_tms, const uint8_t *data_in, size_t cl
static bool jlink_jtag_next(bool tms, bool tdi);
static void jlink_jtag_cycle(bool tms, bool tdi, size_t clock_cycles);

static const uint8_t jlink_switch_to_jtag_seq[9U] = {0xffU, 0xffU, 0xffU, 0xffU, 0xffU, 0xffU, 0xffU, 0x3cU, 0xe7U};

bool jlink_jtag_init(void)
{
DEBUG_PROBE("-> jlink_jtag_init\n");
Expand All @@ -56,7 +54,10 @@ bool jlink_jtag_init(void)

/* Ensure we're in JTAG mode */
DEBUG_PROBE("%s: Switch to JTAG\n", __func__);
if (!jlink_transfer(sizeof(jlink_switch_to_jtag_seq) * 8U, jlink_switch_to_jtag_seq, NULL, NULL)) {
jlink_jtag_cycle(true, false, 56U - 5U);
uint8_t tms_swd_to_jtag_seq[2] = {0x3cU, 0xe7U};
bool res = jlink_transfer(16U, tms_swd_to_jtag_seq, NULL, NULL);
if (!res) {
DEBUG_ERROR("Switch to JTAG failed\n");
return false;
}
Expand Down Expand Up @@ -122,6 +123,17 @@ static bool jlink_jtag_next(bool tms, bool tdi)

static void jlink_jtag_cycle(const bool tms, const bool tdi, const size_t clock_cycles)
{
for (size_t i = 0; i < clock_cycles; i++)
jlink_jtag_next(tms, tdi);
uint8_t tms_buf[8] = {0};
uint8_t tdi_buf[8] = {0};
if (clock_cycles > 64U)
return;
const uint64_t all_ones = clock_cycles == 64U ? UINT64_MAX : (UINT64_C(1) << clock_cycles) - 1U;
const uint64_t tms_pattern = tms ? all_ones : 0U;
const uint64_t tdi_pattern = tdi ? all_ones : 0U;
memcpy(tms_buf, &tms_pattern, 8);
Copy link
Member

@dragonmux dragonmux Feb 2, 2026

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Please use write_le8() here not memcpy() as this makes invalid assumptions about byte layout within a uint64_t that will get violated on the wrong endian system.

memcpy(tdi_buf, &tdi_pattern, 8);
DEBUG_PROBE("jtagtap_cycle tms=%u tdi=%u, clock cycles: %zu\n", tms, tdi, clock_cycles);
const bool result = jlink_transfer(clock_cycles, tms_buf, tdi_buf, NULL);
if (!result)
raise_exception(EXCEPTION_ERROR, "jtagtap_cycle failed");
}
Loading