[meta-xilinx] Zynq TTC usage by Linux

[Edward Wingate]

On Mon, Oct 24, 2016 at 11:16 PM, Mike Looijmans
<mike.looijmans at topic.nl> wrote:
> On 25-10-16 08:03, Edward Wingate wrote:
>> Could you explain about how GPIO hogs eliminate dealing with
>> race-condition prone registers?  Which registers are prone to race
>> conditions in the first place?
>
> For example, to enable the GPIO output mode on MIO pin 0, you'd have to do
> this in bare metal code:
>
> #define ZYNQ_GPIO_DIRM_0        0xE000A204
> #define ZYNQ_GPIO_OEN_0         0xE000A208
> unsigned int reg
> reg = ioread((ZYNQ_GPIO_DIRM_0 + 0));
> iowrite(addr, (ZYNQ_GPIO_OEN_0 + 0) | 0x1);
> reg = ioread((ZYNQ_GPIO_DIRM_0 + 0));
> iowrite(addr, (ZYNQ_GPIO_OEN_0 + 0) | 0x1);
>
> If between reading and writing the registers, the other CPU does something
> similar (e.g. enable output on MIO 1) the result will be undefined.
>
> Setting the GPIO value can be done race-free using the "MASK_DATA_0_LSW"
> register (writing 0xFFFE0001 to address 0xE000A000 will set GPIO 0 to "high"
> without interfering with the other CPU).

Thanks for that, Mike.  This is useful information I don't find anywhere else.

> PS: My generic advice would be to stay away from AMP as far as you possibly
> can. There's hardly any advantage over letting the Linux kernel handle
> things, and the disadvantages are plentiful.

When you need real time control, do you forego Linux and use an RTOS
exclusively?  Or have you used some RT Linux?