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in the middle. The mfree( ) routine is called to free any zero-length
memory buffers.
12
Otherwise, adds the length and sets the next memory buffer in the
chain to the mp mbuf pointer.
9.2.3 Transmitting the Buffer
The following code shows how the el_start_locked( ) routine transmits
the buffer:
WRITE_DATA(sc, len | TX_INT); 1
dat = mtod(ms, unsigned char *);
len = ms->m_len;
while (ms != NULL) {
io_blockwrite((vm_offset_t)dat,
2
sc->data,
(u_long)(len & ~3),
HANDLE_LONGWORD);
dat += (len & ~3);
ms = ms->m_next;
i=len%4;
3
if (ms == NULL) {
if (i) {
val = 0;
for (j=0; j<i; j++)
val |= (*dat++ << (8*j));
WRITE_DATA(sc, val);
}
} else {
if (i) {
val = 0;
for (j=0; j<i; j++)
val |= (*dat++ << (8*j));
dat = mtod(ms, unsigned char *);
if (ms->m_len <= (4-i)) {
for (j=0; j<ms->m_len; j++)
val |= (*dat++ << (8*(j+i)));
ms = NULL;
} else {
len = ms->m_len - (4-i);
for (j=i; j<4; j++)
val |= (*dat++ << (8*j));
}
WRITE_DATA(sc, val);
} else {
dat = mtod(ms, unsigned char *);
len = ms->m_len;
}
}
}
1 Requests an interrupt upon completion of the transmit operation.
9–6 Implementing the Start Section