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SubjectRe: [PATCH 1/3] ARM: dts: omap5-board-common: enable rtc and charging of backup battery
On 13 January 2016 at 19:18, Nishanth Menon <> wrote:
> As you already see it is ridiculously round about way of protecting RTC
> time.. but anyways, for what ever reason, that was mandatory function to
> support on certain product lines.

Having secure date/time is probably necessary for some digital rights
management schemes; e.g. you rent a movie for limited time, but it may
not always be acceptable to require working internet connectivity to
be able to hit the play button hence the need to rely on a secure RTC.

There wouldn't even be an SMC for setting the RTC, probably it would
synchronize when the secure-world shizzle contacts the Big Server
O'Secrety Bits. :P

Protecting pinmux through the L4 firewall sounds hilarious: the whole
ctrl_core module (0x4a002000 - 0x4a002fff) is a single firewall
region. All permitted access to it by linux would have to be
redirected to an SMC or similar.

On 13 January 2016 at 20:05, Nishanth Menon <> wrote:
> An internal feedback I got some time back on AM57 (not OMAP5) - context
> was that we were discussing if an external pull up resistor was needed
> for a GPIO button:
> "Internal pull-ups are relatively weak (ranging to 100kOhm or higher)

Unlike the OMAP5, AM57xx uses 1.8V/3.3V drivers for its generic IOs,
which have to do magic to not get fried by such high voltages.
Crappier specs result, especially for pulling up to 3.3V:
1.8V mode, pull-down current while pin is held high: 50-210 uA
3.3V mode, pull-down current while pin is held high: 40-200 uA
1.8V mode, pull-up current while pin is held low: 60-200 uA
3.3V mode, pull-up current while pin is held low: 10-290 uA

Note the worst-case equivalent pull-up resistance in 3.3V mode is 330
kOhm, eleven times higher than in 1.8V mode.


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