diff --git a/include/config.h b/include/config.h
index c3bb117..fa1e4e3 100644
--- a/include/config.h
+++ b/include/config.h
@@ -154,7 +154,8 @@
 // --- SaltyLab Assignments ---
 // Hoverboard ESC: USART2 (PA2=TX, PA3=RX) or USART3
 // ELRS Receiver: UART4 (PA0=TX, PA1=RX) — CRSF 420000 baud
-// Jetson: USART6 (PC6=TX, PC7=RX)
+// Jetson (JLink binary protocol, Issue #120): USART1 (PB6=TX, PB7=RX) @ 921600
+// USART6 (PC6=TX, PC7=RX): legacy Jetson CDC path — reserved for VESC (Issue #383)
 // Debug: UART5 (PC12=TX, PD2=RX)
 
 // --- ESC Backend Selection (Issue #388) ---
diff --git a/src/jlink.c b/src/jlink.c
index c9a94f3..dba55ec 100644
--- a/src/jlink.c
+++ b/src/jlink.c
@@ -13,6 +13,28 @@ static uint32_t s_rx_tail = 0;     /* consumer index (byte already processed) */
 static UART_HandleTypeDef s_uart;
 static DMA_HandleTypeDef  s_dma_rx;
 
+/* ---- TX mutex ---- */
+/*
+ * Issue #522: USART1 IDLE interrupt (DMA RX) fires via HAL_UART_IRQHandler
+ * mid-frame during polling HAL_UART_Transmit, resetting gState and causing
+ * truncated/null-prefixed frames on the Jetson link.
+ *
+ * Fix: disable USART1_IRQn around every blocking TX so HAL_UART_IRQHandler
+ * cannot modify gState while HAL_UART_Transmit is looping.  s_tx_busy guards
+ * against any re-entrant caller (ESC debug, future paths).
+ */
+static volatile uint8_t s_tx_busy = 0;
+
+static void jlink_tx_locked(uint8_t *buf, uint16_t len)
+{
+    if (s_tx_busy) return;          /* drop if already transmitting */
+    s_tx_busy = 1u;
+    HAL_NVIC_DisableIRQ(USART1_IRQn);
+    HAL_UART_Transmit(&s_uart, buf, len, 5u);
+    HAL_NVIC_EnableIRQ(USART1_IRQn);
+    s_tx_busy = 0u;
+}
+
 /* ---- Volatile state ---- */
 volatile JLinkState jlink_state;
 
@@ -293,7 +315,7 @@ void jlink_send_telemetry(const jlink_tlm_status_t *status)
     frame[3 + plen + 1] = (uint8_t)(crc & 0xFFu);
     frame[3 + plen + 2] = JLINK_ETX;
 
-    HAL_UART_Transmit(&s_uart, frame, sizeof(frame), 5u);
+    jlink_tx_locked(frame, sizeof(frame));
 }
 
 /* ---- jlink_send_power_telemetry() ---- */
@@ -318,5 +340,5 @@ void jlink_send_power_telemetry(const jlink_tlm_power_t *power)
     frame[3 + plen + 1] = (uint8_t)(crc & 0xFFu);
     frame[3 + plen + 2] = JLINK_ETX;
 
-    HAL_UART_Transmit(&s_uart, frame, sizeof(frame), 5u);
+    jlink_tx_locked(frame, sizeof(frame));
 }