Re: [Qemu-trivial] [Qemu-devel] [PATCH v2 02/14] sm501: Use defines instead of constants where available

[Peter Maydell]

On 2 March 2017 at 18:53, Peter Maydell <address@hidden> wrote:
> On 7 November 2016 at 09:03, BALATON Zoltan <address@hidden> wrote:
> I just found a datasheet which says that the power-on-default
> for the misc-control register is 0b0000.0000.0000.00x0.0001.0000.xxx0.0xxx
> which means that the 0x1000 decimal value is correct and setting
> the IRQ_INVERT bit is wrong.
>
> I think the "active=low" bit is referencing the fact that the
> DAC_POWER bit is 1 for "disable" and 0 for "enable".

Actually it's referring to bit 17 (which is an "X" in the reset value
above), which is documented as being set by a GPIO pin on reset,
and having different meanings for SH and SA1110. In this case we're
saying 'reset bit 17 to 0, meaning "SH series CPU, Active Low"'.

Note also that the low bits indicate the bus type which is 000 for
SH and 001 for PCI, etc.

So a better comment here would be:
    /* Bits 17 (SH), 7 (CDR), 6:5 (Test), 2:0 (Bus) are all supposed
     * to be determined at reset by GPIO lines which set config bits.
     * We hardwire them:
     *  SH = 0 : Hitachi Ready Polarity == Active Low
     *  CDR = 0 : do not reset clock divider
     *  TEST = 0 : Normal mode (not testing the silicon)
     *  BUS = 0 : Hitachi SH3/SH4
     */
    s->misc_control = SM501_MISC_DAC_POWER;

...and you'll want to put something in to get the right Bus value
for the PCI version.

thanks
-- PMM