<blockquote>
<p>Can you try with this patch?</p>
<div class="highlight highlight-source-diff"><pre><span class="pl-md">--- a/cpu/cc2538/periph/spi.c</span>
<span class="pl-mi1">+++ b/cpu/cc2538/periph/spi.c</span>
<span class="pl-mdr">@@ -150,9 +150,8 @@</span> void spi_transfer_bytes(spi_t bus, spi_cs_t cs, bool cont,
         for (size_t i = 0; i < len; i++) {
             while (!(dev(bus)->SR & SSI_SR_TNF)) {}
             dev(bus)->DR = 0;
<span class="pl-md"><span class="pl-md">-</span>            if (dev(bus)->SR & SSI_SR_RNE) {</span>
<span class="pl-md"><span class="pl-md">-</span>                in_buf[in_cnt++] = dev(bus)->DR;</span>
<span class="pl-md"><span class="pl-md">-</span>            }</span>
<span class="pl-mi1"><span class="pl-mi1">+</span>            while (!(dev(bus)->SR & SSI_SR_RNE)) {}</span>
<span class="pl-mi1"><span class="pl-mi1">+</span>            in_buf[in_cnt++] = dev(bus)->DR;</span>
         }
         /* get remaining bytes */
         while (dev(bus)->SR & SSI_SR_RNE) {</pre></div>
</blockquote>
<p>Great succes!</p>
<div class="highlight highlight-source-shell"><pre>ping6 fe80::2068:3123:9df1:9637%7
2019-09-30 13:11:58,559 - INFO <span class="pl-c"><span class="pl-c">#</span> ping6 fe80::2068:3123:9df1:9637%7</span>
2019-09-30 13:11:58,575 - INFO <span class="pl-c"><span class="pl-c">#</span> 12 bytes from fe80::2068:3123:9df1:9637: icmp_seq=0 ttl=64 rssi=-17 dBm time=11.283 ms</span>
2019-09-30 13:11:59,572 - INFO <span class="pl-c"><span class="pl-c">#</span> 12 bytes from fe80::2068:3123:9df1:9637: icmp_seq=1 ttl=64 rssi=-17 dBm time=11.283 ms</span>
2019-09-30 13:12:00,580 - INFO <span class="pl-c"><span class="pl-c">#</span> 12 bytes from fe80::2068:3123:9df1:9637: icmp_seq=2 ttl=64 rssi=-17 dBm time=11.283 ms</span>
2019-09-30 13:12:00,581 - INFO <span class="pl-c"><span class="pl-c">#</span> </span>
2019-09-30 13:12:00,584 - INFO <span class="pl-c"><span class="pl-c">#</span> --- fe80::2068:3123:9df1:9637 PING statistics ---</span>
2019-09-30 13:12:00,592 - INFO <span class="pl-c"><span class="pl-c">#</span> 3 packets transmitted, 3 packets received, 0% packet loss</span>
2019-09-30 13:12:00,595 - INFO <span class="pl-c"><span class="pl-c">#</span> round-trip min/avg/max = 11.283/11.283/11.283 ms</span></pre></div>

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