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[media] e4000: implement DC offset correction

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I did some tests against modulator (television signal generator) and this
seems to improve sensitivity a little bit on channel I used. Used device
was able to receive transmission just as weak signal as with Windows XP.
Thanks to Jacek for donating his non-working device. I cannot ask he to
test anymore...

Reported-by: Jacek Konieczny <jajcus@jajcus.net>
Signed-off-by: Antti Palosaari <crope@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>
This commit is contained in:
Antti Palosaari 2013-07-24 02:04:12 -03:00 committed by Mauro Carvalho Chehab
parent 83453a7cc8
commit 8514611438
1 changed files with 48 additions and 8 deletions
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56
drivers/media/tuners/e4000.c
View file

@ -140,14 +140,12 @@ static int e4000_init(struct dvb_frontend *fe)
if (ret < 0)
goto err;
/*
* TODO: Implement DC offset control correctly.
* DC offsets has quite much effect for received signal quality in case
* of direct conversion tuners (Zero-IF). Surely we will now lose few
* decimals or even decibels from SNR...
*/
/* DC offset control */
ret = e4000_wr_reg(priv, 0x2d, 0x0c);
ret = e4000_wr_reg(priv, 0x2d, 0x1f);
if (ret < 0)
goto err;
ret = e4000_wr_regs(priv, 0x70, "\x01\x01", 2);
if (ret < 0)
goto err;
@ -204,7 +202,7 @@ static int e4000_set_params(struct dvb_frontend *fe)
struct dtv_frontend_properties *c = &fe->dtv_property_cache;
int ret, i, sigma_delta;
unsigned int f_VCO;
u8 buf[5];
u8 buf[5], i_data[4], q_data[4];
dev_dbg(&priv->i2c->dev, "%s: delivery_system=%d frequency=%d " \
"bandwidth_hz=%d\n", __func__,
@ -292,6 +290,48 @@ static int e4000_set_params(struct dvb_frontend *fe)
if (ret < 0)
goto err;
/* DC offset */
for (i = 0; i < 4; i++) {
if (i == 0)
ret = e4000_wr_regs(priv, 0x15, "\x00\x7e\x24", 3);
else if (i == 1)
ret = e4000_wr_regs(priv, 0x15, "\x00\x7f", 2);
else if (i == 2)
ret = e4000_wr_regs(priv, 0x15, "\x01", 1);
else
ret = e4000_wr_regs(priv, 0x16, "\x7e", 1);
if (ret < 0)
goto err;
ret = e4000_wr_reg(priv, 0x29, 0x01);
if (ret < 0)
goto err;
ret = e4000_rd_regs(priv, 0x2a, buf, 3);
if (ret < 0)
goto err;
i_data[i] = (((buf[2] >> 0) & 0x3) << 6) | (buf[0] & 0x3f);
q_data[i] = (((buf[2] >> 4) & 0x3) << 6) | (buf[1] & 0x3f);
}
buf[0] = q_data[0];
buf[1] = q_data[1];
buf[2] = q_data[3];
buf[3] = q_data[2];
ret = e4000_wr_regs(priv, 0x50, buf, 4);
if (ret < 0)
goto err;
buf[0] = i_data[0];
buf[1] = i_data[1];
buf[2] = i_data[3];
buf[3] = i_data[2];
ret = e4000_wr_regs(priv, 0x60, buf, 4);
if (ret < 0)
goto err;
/* gain control auto */
ret = e4000_wr_reg(priv, 0x1a, 0x17);
if (ret < 0)