<p>add printf code in enc28j60.c , as</p>
<pre><code>static void cmd_bfs(enc28j60_t *dev, uint8_t reg, int8_t bank, uint8_t mask)
{
    spi_acquire(SPI_BUS, CS_PIN, SPI_MODE_0, SPI_CLK);
    switch_bank(dev, bank);
    printf("cmd_bfs\n");
    spi_transfer_reg(SPI_BUS, CS_PIN, (CMD_BFS | reg), mask);
    printf("cmd_bfs 2\n");
    spi_release(SPI_BUS);
}
</code></pre>
<p>and finally die in spi_transfer_reg , here is log :</p>
<pre><code>2019-09-25 16:11:35,686 - INFO # send 4 bytes, value=634
2019-09-25 16:11:35,689 - INFO # cmd_bfs
2019-09-25 16:11:35,689 - INFO # cmd_bfs 2
2019-09-25 16:11:35,690 - INFO # cmd_bfs
2019-09-25 16:11:35,693 - INFO # cmd_bfs 2
2019-09-25 16:11:35,694 - INFO # send 4 bytes, value=635
2019-09-25 16:11:35,696 - INFO # cmd_bfs
2019-09-25 16:11:35,697 - INFO # cmd_bfs 2
2019-09-25 16:11:35,697 - INFO # cmd_bfs
2019-09-25 16:11:35,701 - INFO # cmd_bfs 2
2019-09-25 16:11:35,701 - INFO # send 4 bytes, value=636
2019-09-25 16:11:35,704 - INFO # cmd_bfs

</code></pre>
<p>enc28j60 and w5100 are base  on spi,  maybe the bug is in SPI driver</p>

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