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PC Chipset: Improve serial divisor calculation 

This fixes several problems I found in the UART serial implementation.
Now all divisor values are allowed, while before divisor values of zero
and below the base baud rate were rejected. All changes are in reference
to http://www.sci.muni.cz/docs/pc/serport.txt

Signed-off-by: Calvin Lee <cyrus296@gmail.com>
Message-Id: <20180512000545.966-2-cyrus296@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Calvin Lee 2018-05-11 18:05:44 -06:00 committed by Paolo Bonzini
parent 9ee8a692f1
commit 0147883450
1 changed files with 13 additions and 10 deletions
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21
hw/char/serial.c
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@ -150,13 +150,10 @@ static void serial_update_irq(SerialState *s)
static void serial_update_parameters(SerialState *s)
{
int speed, parity, data_bits, stop_bits, frame_size;
float speed;
int parity, data_bits, stop_bits, frame_size;
QEMUSerialSetParams ssp;
if (s->divider == 0 || s->divider > s->baudbase) {
return;
}
/* Start bit. */
frame_size = 1;
if (s->lcr & 0x08) {
@ -169,14 +166,16 @@ static void serial_update_parameters(SerialState *s)
} else {
parity = 'N';
}
if (s->lcr & 0x04)
if (s->lcr & 0x04) {
stop_bits = 2;
else
} else {
stop_bits = 1;
}
data_bits = (s->lcr & 0x03) + 5;
frame_size += data_bits + stop_bits;
speed = s->baudbase / s->divider;
/* Zero divisor should give about 3500 baud */
speed = (s->divider == 0) ? 3500 : (float) s->baudbase / s->divider;
ssp.speed = speed;
ssp.parity = parity;
ssp.data_bits = data_bits;
@ -184,7 +183,7 @@ static void serial_update_parameters(SerialState *s)
s->char_transmit_time = (NANOSECONDS_PER_SECOND / speed) * frame_size;
qemu_chr_fe_ioctl(&s->chr, CHR_IOCTL_SERIAL_SET_PARAMS, &ssp);
DPRINTF("speed=%d parity=%c data=%d stop=%d\n",
DPRINTF("speed=%.2f parity=%c data=%d stop=%d\n",
speed, parity, data_bits, stop_bits);
}
@ -341,7 +340,11 @@ static void serial_ioport_write(void *opaque, hwaddr addr, uint64_t val,
default:
case 0:
if (s->lcr & UART_LCR_DLAB) {
if (size == 2) {
s->divider = (s->divider & 0xff00) | val;
} else if (size == 4) {
s->divider = val;
}
serial_update_parameters(s);
} else {
s->thr = (uint8_t) val;