diff --git a/modules/drivers/digilent_jtag/digilent_jtag_drv.c b/modules/drivers/digilent_jtag/digilent_jtag_drv.c
index 651f795..0a6bf52 100644
--- a/modules/drivers/digilent_jtag/digilent_jtag_drv.c
+++ b/modules/drivers/digilent_jtag/digilent_jtag_drv.c
@@ -285,26 +285,26 @@ static int drv_Digilent_DeInit(jtag_core *jc)
 
 static int drv_Digilent_TMS_xfer(jtag_core *jc, unsigned char *str_out, int size)
 {
-    DJ_BYTE buf_snd[1024];
+    DJ_BYTE *buf_snd;
     int nbytes = (size + 7) / 8;
-    int i;
+    int i, ok;
 
     if (!g_dj_open) return JTAG_CORE_BAD_PARAMETER;
     if (size <= 0)  return JTAG_CORE_NO_ERROR;
-    if (nbytes > (int)sizeof(buf_snd)) {
-        jtagcore_logs_printf(jc, MSG_ERROR,
-            "drv_Digilent_TMS_xfer : size %d > %d bits\r\n",
-            size, (int)sizeof(buf_snd) * 8);
-        return JTAG_CORE_BAD_PARAMETER;
-    }
 
-    memset(buf_snd, 0, nbytes);
+    /* Heap-allocated and sized to the shift: a bitstream load shifts
+     * millions of bits in one call, far past any fixed buffer. */
+    buf_snd = calloc(1, (size_t)nbytes);
+    if (!buf_snd) return JTAG_CORE_BAD_PARAMETER;
+
     for (i = 0; i < size; i++) {
         if (str_out[i] & JTAG_STR_TMS)
             buf_snd[i >> 3] |= (DJ_BYTE)(1u << (i & 7));
     }
 
-    if (!g_dj.PutTmsBits(g_dj_hif, /*fTdi=*/0, buf_snd, NULL, (DJ_DWORD)size, /*fOverlap=*/0)) {
+    ok = g_dj.PutTmsBits(g_dj_hif, /*fTdi=*/0, buf_snd, NULL, (DJ_DWORD)size, /*fOverlap=*/0);
+    free(buf_snd);
+    if (!ok) {
         jtagcore_logs_printf(jc, MSG_ERROR,
             "drv_Digilent_TMS_xfer : DjtgPutTmsBits failed\r\n");
         return JTAG_CORE_BAD_PARAMETER;
@@ -317,10 +317,9 @@ static int drv_Digilent_TDOTDI_xfer(jtag_core *jc,
                                     unsigned char *str_in,
                                     int size)
 {
-    DJ_BYTE buf_snd[2048];
-    DJ_BYTE buf_rcv[1024];
+    DJ_BYTE *buf_snd, *buf_rcv = NULL;
     int has_tms = 0;
-    int i;
+    int i, ok, snd_bytes;
 
     if (!g_dj_open) return JTAG_CORE_BAD_PARAMETER;
     if (size <= 0)  return JTAG_CORE_NO_ERROR;
@@ -329,54 +328,50 @@ static int drv_Digilent_TDOTDI_xfer(jtag_core *jc,
         if (str_out[i] & JTAG_STR_TMS) { has_tms = 1; break; }
     }
 
+    if (str_in) {
+        buf_rcv = calloc(1, (size_t)((size + 7) / 8));
+        if (!buf_rcv) return JTAG_CORE_BAD_PARAMETER;
+    }
+
+    /* PutTmsTdiBits packs 2 bits/clock, PutTdiBits 1 bit/clock. Buffers
+     * are heap-sized to the shift (bitstream loads run into MB). */
+    snd_bytes = has_tms ? (2 * size + 7) / 8 : (size + 7) / 8;
+    buf_snd = calloc(1, (size_t)snd_bytes);
+    if (!buf_snd) { free(buf_rcv); return JTAG_CORE_BAD_PARAMETER; }
+
     if (has_tms) {
-        /* Mixed TMS+TDI shift: 2 bits per clock (TDI low, TMS high), LSB-first. */
-        int nbytes_snd = (2 * size + 7) / 8;
-        if (nbytes_snd > (int)sizeof(buf_snd) || (size + 7) / 8 > (int)sizeof(buf_rcv)) {
-            jtagcore_logs_printf(jc, MSG_ERROR,
-                "drv_Digilent_TDOTDI_xfer : size %d too large\r\n", size);
-            return JTAG_CORE_BAD_PARAMETER;
-        }
-        memset(buf_snd, 0, nbytes_snd);
+        /* 2 bits per clock: TDI low, TMS high, LSB-first. */
         for (i = 0; i < size; i++) {
             int pos = 2 * i;
             if (str_out[i] & JTAG_STR_DOUT)
-                buf_snd[pos >> 3] |= (DJ_BYTE)(1u << (pos & 7));     /* TDI = low bit */
+                buf_snd[pos >> 3] |= (DJ_BYTE)(1u << (pos & 7));
             pos++;
             if (str_out[i] & JTAG_STR_TMS)
-                buf_snd[pos >> 3] |= (DJ_BYTE)(1u << (pos & 7));     /* TMS = high bit */
-        }
-        if (!g_dj.PutTmsTdiBits(g_dj_hif, buf_snd, str_in ? buf_rcv : NULL,
-                                (DJ_DWORD)size, /*fOverlap=*/0)) {
-            jtagcore_logs_printf(jc, MSG_ERROR,
-                "drv_Digilent_TDOTDI_xfer : DjtgPutTmsTdiBits failed\r\n");
-            return JTAG_CORE_BAD_PARAMETER;
+                buf_snd[pos >> 3] |= (DJ_BYTE)(1u << (pos & 7));
         }
+        ok = g_dj.PutTmsTdiBits(g_dj_hif, buf_snd, buf_rcv, (DJ_DWORD)size, /*fOverlap=*/0);
     } else {
         /* Pure data shift: TMS held to 0, 1 bit per clock. */
-        int nbytes_snd = (size + 7) / 8;
-        if (nbytes_snd > (int)sizeof(buf_rcv)) {
-            jtagcore_logs_printf(jc, MSG_ERROR,
-                "drv_Digilent_TDOTDI_xfer : size %d too large\r\n", size);
-            return JTAG_CORE_BAD_PARAMETER;
-        }
-        memset(buf_snd, 0, nbytes_snd);
         for (i = 0; i < size; i++) {
             if (str_out[i] & JTAG_STR_DOUT)
                 buf_snd[i >> 3] |= (DJ_BYTE)(1u << (i & 7));
         }
-        if (!g_dj.PutTdiBits(g_dj_hif, /*fTms=*/0, buf_snd, str_in ? buf_rcv : NULL,
-                             (DJ_DWORD)size, /*fOverlap=*/0)) {
-            jtagcore_logs_printf(jc, MSG_ERROR,
-                "drv_Digilent_TDOTDI_xfer : DjtgPutTdiBits failed\r\n");
-            return JTAG_CORE_BAD_PARAMETER;
-        }
+        ok = g_dj.PutTdiBits(g_dj_hif, /*fTms=*/0, buf_snd, buf_rcv, (DJ_DWORD)size, /*fOverlap=*/0);
+    }
+    free(buf_snd);
+
+    if (!ok) {
+        free(buf_rcv);
+        jtagcore_logs_printf(jc, MSG_ERROR,
+            "drv_Digilent_TDOTDI_xfer : Djtg shift failed (size %d)\r\n", size);
+        return JTAG_CORE_BAD_PARAMETER;
     }
 
     if (str_in) {
         for (i = 0; i < size; i++) {
             str_in[i] = (buf_rcv[i >> 3] & (1u << (i & 7))) ? JTAG_STR_DOUT : 0;
         }
+        free(buf_rcv);
     }
     return JTAG_CORE_NO_ERROR;
 }