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Feature: implementation of jtagtap_cycle for JLink backend #2182

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Merged
dragonmux merged 3 commits into from
Feb 6, 2026
Merged

Feature: implementation of jtagtap_cycle for JLink backend #2182

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aa230f0
hosted/jlink: Use jtagtap_cycle to switch from SWD to JTAG
ALTracer Jan 29, 2026
774a1b9
hosted/jlink: Implement jtagtap_cycle via jlink_transfer
ALTracer Jan 29, 2026
82a0581
hosted/jlink: Rewrite jtagtap_cycles using plain for-loops and bitmas…
ALTracer Feb 4, 2026
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26 changes: 21 additions & 5 deletions src/platforms/hosted/jlink_jtag.c
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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 +123,21 @@ 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[512] = {0};
uint8_t tdi_buf[512] = {0};
if (clock_cycles > 4096U)
return;
const size_t clock_bytes = clock_cycles >> 3U;
memset(tms_buf, tms ? 0xffU : 0U, clock_bytes);
memset(tdi_buf, tdi ? 0xffU : 0U, clock_bytes);
const size_t clock_bits = clock_cycles & 7U;
if (clock_bits) {
const uint8_t ones = (1U << clock_bits) - 1U;
tms_buf[clock_bytes] = tms ? ones : 0U;
tdi_buf[clock_bytes] = tdi ? ones : 0U;
}
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");
}
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