Messages in this thread | | | Date | Mon, 2 Mar 2015 22:29:45 +0100 | From | Pavel Machek <> | Subject | Re: [PATCH 14/15] twl4030_charger: Increase current carefully while watching voltage. |
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On Tue 2015-02-24 15:33:53, NeilBrown wrote: > The USB Battery Charging spec (BC1.2) suggests a dedicated > charging port can deliver from 0.5 to 5.0A at between 4.75 and 5.25 > volts. > > To choose the "correct" current voltage setting requires a trial > and error approach: try to draw current and see if the voltage drops > too low. > > Even with a configure Standard Downstream Port, it may not be possible > to reliably pull 500mA - depending on cable quality and source
"configured"?
> quality I have reports of charging failure due to the voltage dropping > too low. > > To address both these concern, this patch introduce incremental
concerns.
> current setting. > The current pull from VBUS is increased in steps of 20mA every 100ms > until the target is reached or until the measure voltage drops below > 4.75V. If the voltage does go too long, the target current is reduced
"too low"?
> by 20mA and kept there. > > This applies to currents selected automatically, or to values > set via sysfs. So setting a large value will cause the maximum > available to be used - up to the limit of 1.7mA imposed by the > hardware.
1.7A?
> @@ -249,8 +261,14 @@ static int twl4030_charger_update_current(struct twl4030_bci *bci) > cur = bci->ac_cur; > bci->ac_is_active = 1; > } else { > - cur = bci->usb_cur; > + cur = bci->usb_cur_actual;
usb_cur_actual is not a really great variable name...
> bci->ac_is_active = 0; > + if (cur > bci->usb_cur) { > + cur = bci->usb_cur; > + bci->usb_cur_actual = cur; > + } > + if (cur < bci->usb_cur) > + schedule_delayed_work(&bci->current_worker, USB_CUR_DELAY); > } > > /* First, check thresholds and see if cgain is needed */ > @@ -379,6 +397,38 @@ static int twl4030_charger_update_current(struct twl4030_bci *bci) > return 0; > } > > +static void twl4030_current_worker(struct work_struct *data) > +{ > + int v; > + int res; > + struct twl4030_bci *bci = container_of(data, struct twl4030_bci, > + current_worker.work); > + > + res = twl4030bci_read_adc_val(TWL4030_BCIVBUS); > + if (res < 0) > + v = 0; > + else > + /* BCIVBUS uses ADCIN8, 7/1023 V/step */ > + v = res * 6843; > + > + printk("v=%d cur=%d target=%d\n", v, bci->usb_cur_actual, > + bci->usb_cur); > + > + if (v < USB_MIN_VOLT) { > + /* Back up and stop adjusting. */ > + bci->usb_cur_actual -= USB_CUR_STEP; > + bci->usb_cur = bci->usb_cur_actual; > + } else if (bci->usb_cur_actual >= bci->usb_cur || > + bci->usb_cur_actual + USB_CUR_STEP > USB_MAX_CURRENT) { > + /* Reach target and volts are OK - stop */
Reached ... and the voltage is OK - stop.
-- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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