Re: Looking for issues/features for my first contribution

[Rajath Shashidhara <rajaths@cs.utexas.edu>]

On 07-11-2019 07:33, Aleksandar Markovic wrote:
> 
> I did a quick Google search on datasheets of existing RTC
> implemtations, and the result is:
> 
> DS1338: https://datasheets.maximintegrated.com/en/ds/DS1338-DS1338Z.pdf
> M41T80: https://www.st.com/resource/en/datasheet/m41t80.pdf
> M48T59: http://www.elektronikjk.pl/elementy_czynne/IC/M48T59V.pdf
> MC146818: https://www.nxp.com/docs/en/data-sheet/MC146818.pdf
> PL031: http://infocenter.arm.com/help/topic/com.arm.doc.ddi0224c/real_time_clock_pl031_r1p3_technical_reference_manual_DDI0224C.pdf
> TWL92230: https://datasheet.octopart.com/TWL92230C-Texas-Instruments-datasheet-150321.pdf
> Zynq RTC: https://www.xilinx.com/support/documentation/user_guides/ug1085-zynq-ultrascale-trm.pdf
> (chapter 7)

I have a few questions about this:
[a] Is there any particular reason that you picked DS3231 ? Linux kernel 
has drivers for DS3232/34 only [1]. I did read the datasheets of both 
3232 & 3231 and found that they are quite similar except for the 236 
bytes of SRAM support found only in 3232.

[b] As per the datasheet, DS3231 has a built-in temperature sensor. 
Temperature can be read from a dedicated register. There can be two 
approaches to emulating this: (1) Return a constant temperature value on 
every read (2) Throw a not-supported exception/warning. What is the qemu 
convention for handling such features ?

[c] DS3231 also has programmable square-wave output + 32 KHz output pin. 
M41T80 chip also supports this feature. However, qemu does not support 
emulation of these features [2]. Do I take the same approach ?

Thanks!
Rajath Shashidhara

References:
[1] 
https://elixir.bootlin.com/linux/v5.4-rc6/source/drivers/rtc/rtc-ds3232.c
[2] 
https://git.qemu.org/?p=qemu.git;a=blob;f=hw/rtc/m41t80.c;h=914ecac8f4db418633d6daf92608cb50f6b89052;hb=HEAD