Re: [Qemu-devel] qemu-system-sh4 -M r2d serial is broken.

[Paolo Bonzini <pbonzini@redhat.com>]

On 18/05/2017 22:10, Aurelien Jarno wrote:
> On 2017-05-18 21:57, Paolo Bonzini wrote:
>> Anyway, Uli Hecht is saying SCIF "asserts DR even if the FIFO threshold
>> has not been reached if no data is received for 1.5 frames".  If that's
>> just a register and doesn't trigger an interrupt, you can compute the
>> bit's value dynamically based on the current clock.
>>
>> This is for example how the x86 RTC chip computes the "update in
>> progress" bit, which is set for 220 us before the RC updates.  Doing
>> that with a timer would be really imprecise.
> 
> Unfortunately, the DR bit is set to 1 after 1.5 frames (so the exact
> timing depends on the actual baud rate), and that also triggers an
> interrupt if the RIE bit is set to 1. I haven't checked yet if the
> kernel relies on the bit or the interrupt or both.

DR only generates interrupts in asynchronous mode according to the data
sheet I found
(http://datasheet.octopart.com/DF72115D160FPV-Renesas-datasheet-11797591.pdf).

Paolo