On Sun, Dec 22, 2019 at 8:44 PM Christian Mauderer <l...@c-mauderer.de> wrote:
> Hello Niteesh, > > thanks for doing that work. > > On 22/12/2019 12:10, Niteesh wrote: > > The rpi1 and rpi2 use the PL011 UART, whereas, with RPI's equipped with > > wireless/Bluetooth module, the PL011 is connected to the Bluetooth > > module, and the mini UART is used as the primary UART. > > In my opinion it would be great if you could use the FDT to distinguish > between the boards. That should allow to add raspberry 3 (and maybe 4) > support without adding another BSP. More BSPs mean a bigger maintenance > effort for the RTEMS community. Learning more about FDT is on my list for a long time. I would love to work on that but I have almost no exp with FDT's. But another thing could also be done, in raspberrypi/start/bspstart.c we get the revision and model of the board using the mailbox. Every board has a unique id, which we could use to initialize the BSP. But using FDT seems to be a more elegant option, it is a lot of work I think, but we could take help from libbsd and linux I suppose. What do you think? > > > > > https://www.raspberrypi.org/app/uploads/2012/02/BCM2835-ARM-Peripherals.pdf > > But from the above doc (PAGE 10), the mini uart has 16550 like registers > > and RTEMS already has the driver for it > > bsps/shared/dev/serial/ns16550.c. But I am not sure how compatible they > > are? Should a new driver be implemented from scratch or use ns16550 if > > possible? > > In general it's better to re-use existing code. That has multiple > advantages: > > - It reduces the maintenance effort. Fewer code means fewer work. > - If you have multiple driver for the same or similar hardware it can > happen that a bug is fixed in one but not the other. > - It's simpler to find a hardware to test changes. > - The driver becomes more universal with every new supported hardware. > That increases the chance that it fits the next new hardware. > > I'm sure there are some more if you ask someone else. I do understand the issues, I just spent some time reading the driver code. I think we could most probably use it. I will take a closer look and will update. > > > > > Also, the core clock on which the PL011 is based on is changed in rpi3. > > Rpi1 and 2 use 250Mhz as the default clock but it was changed to 400Mhz > > in Rpi3 and newer > > Again: Would be great if that could be adapted based on FDT or by > reading the right registers. > > > > > Few differences between PL011 and Mini uart > > The mini UART has smaller FIFOs. Combined with the lack of flow control, > > this makes it more prone to losing characters at higher baud rates. It > > is also generally less capable than the PL011, mainly due to its baud > > rate link to the VPU clock speed. > > That shouldn't really be a problem for the system console. > > > > > The particular deficiencies of the mini UART compared to the PL011 are : > > > > No break detection > > No framing errors detection > > No parity bit > > No receive timeout interrupt > > No DCD, DSR, DTR or RI signals > > >
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