Re: [Gumstix-users] Configuring BB_CFG and BOOT_CFG via I2C for backup battery usage and charging

[Bob C. <bco...@ve...>]

Chris,

What size and type of battery are you using?

Thanks

Bob Cochran



On 12/23/2010 02:59 PM, Chris MacDonald wrote:
> Hi All,
>
> I've got an Overo Water on a Tobi expansion board and I'm attempting
> to use a battery to keep the RTC going in the event the device is
> powered down. I've been reading through manuals and I've established
> that the BB_CFG register must be changed to allow for charging of the
> backup battery, and BOOT_CFG can be changed to save some power by
> putting a 32kHz clock in low power mode (this is all from
> http://focus.ti.com.cn/cn/general/docs/lit/getliterature.tsp?literatureNumber=swca025&fileType=pdf).
>
> I'm running in to problems actually writing values using I2C. I'm
> using i2cget/i2cset from the command line to read and write registers,
> and as a test, I can run
>
> root@overo:~# i2cget -y -f 1 0x4a 0xee
> 0x33
> root@overo:~# i2cset -y -f 1 0x4a 0xee 0x00
> root@overo:~# i2cget -y -f 1 0x4a 0xee
> 0x00
> root@overo:~# i2cset -y -f 1 0x4a 0xee 0x33
> root@overo:~# i2cget -y -f 1 0x4a 0xee
> 0x33
>
> and all appears well; the power LED turns off and back on as expected.
> However, when I attempt to change the values of BB_CFG, as far as I
> can tell, nothing happens
>
> root@overo:~# i2cget -y -f 1 0x4a 0x6d
> 0x00
> root@overo:~# i2cset -y -f 1 0x4a 0x6d 0x14
> root@overo:~# i2cget -y -f 1 0x4a 0x6d
> 0x00
>
> and this should enable charging at 25uA, stopping at 3.1V; I'm not
> sure if it's supposed to return 0x00 or not (I'm assuming not though).
> The same is true when I try to set BOOT_CFG (always returns 0x00). In
> the reference manual for the TPS65950 both registers are said to be
> write-protected using KEY_CFG, and as far as I can understand from the
> TRM to enable writing I need to send 0xc0 then 0x0c to PROTECT_KEY and
> reading from PROTECT_KEY will return values indicating whether writing
> to protected registers is enabled. I've tried this and PROTECT_KEY
> always returns 0x00.
>
> It seems to me that I'm doing something wrong here, but I don't know
> what. Does anyone see a problem with this approach? Has anyone done
> this before, who might be able to shed some light on either what I'm
> doing wrong, or what they've done to enable this functionality?
>
> Thanks in advance,
> Chris
>
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