From bddfe9799752e819561734c08058e7e02965ad9c Mon Sep 17 00:00:00 2001
From: Andrew Dennison <andrew@motec.com.au>
Date: Mon, 29 May 2023 11:19:12 +1000
Subject: [PATCH] jlink: suport writeTDI() with tx=NULL

fixes crash and is consistent with other jtag cables
---
 src/jlink.cpp | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/jlink.cpp b/src/jlink.cpp
index af55a2b..4df3679 100644
--- a/src/jlink.cpp
+++ b/src/jlink.cpp
@@ -137,7 +137,10 @@ int Jlink::writeTDI(uint8_t *tx, uint8_t *rx, uint32_t len, bool end)
 			xfer_len = len - rest;  // reduce xfer len
 		uint16_t tt = (xfer_len + 7) >> 3;  // convert to Byte
 		memset(_tms, tms, tt);  // fill tms buffer
-		memcpy(_tdi, tx_ptr, tt);  // fill tdi buffer
+		if (tx)
+			memcpy(_tdi, tx_ptr, tt);  // fill tdi buffer
+		else
+			memset(_tdi, 0, tt);  // clear tdi buffer
 		_num_bits = xfer_len;  // set buffer size in bit
 		if (end && xfer_len + rest == len) {  // last sequence: set tms 1
 			_last_tms = 1;