Re: [Qemu-devel] high resolution timer question
Robert Reif wrote: Characters written to serial port A are not reliably making it to the screen. Turning on serial debugging shows that the characters are written to the serial port. The characters do make it to the screen when debugging. The problem seems to be caused by multiple streams outputting to the screen. It looks like different ways of outputting to the same device may use different streams! Please disregard this possible cause. I left a debugging printf in by accident. The real problem is still there though.
Re: [Qemu-devel] high resolution timer question
Robert Reif wrote: The problem I'm having is with sparc32 using a sun openboot image in nographics mode where the prom uses serial port A as the system console. The serial port output shows up in the host terminal window that qemu was started in. Characters written to serial port A are not reliably making it to the screen. Turning on serial debugging shows that the characters are written to the serial port. The characters do make it to the screen when debugging. The problem seems to be caused by multiple streams outputting to the screen. It looks like different ways of outputting to the same device may use different streams!
Re: [Qemu-devel] high resolution timer question
Blue Swirl wrote: On 12/10/07, Robert Reif <[EMAIL PROTECTED]> wrote: Writing data to a serial port on the sparc emulation happens immediately. I would like to throttle the write speed to match the actual baud rate. What's the best way to do this in qemu? Will QEMUTimer work for a 1 millisecond timer? Do you mean that you want the serial port to match the host speed so that for example, at 9600 baud, target would only receive 9600 bits per second? Or do you mean that the emulated CPU should see bits arriving at the same rate that the real CPU would see compared to CPU execution speed? On the positive side, this would fix a bug with serial interrupts arriving too fast which can trigger Linux panics. But this would also complicate the design because currently the devices do not need to emulate any internal buffers. The problem I'm having is with sparc32 using a sun openboot image in nographics mode where the prom uses serial port A as the system console. The serial port output shows up in the host terminal window that qemu was started in. Characters written to serial port A are not reliably making it to the screen. Turning on serial debugging shows that the characters are written to the serial port. The characters do make it to the screen when debugging. If characters are not queued, then that might explain the loss but it looks like the characters are going to a write(fd, ...) so is stdio loosing the characters? I thought slowing down the rate to realistic speeds might help but that doesn't seem to be where the problem really is.
Re: [Qemu-devel] high resolution timer question
> > I think the throttling should be done at CharDriver level so that all > > targets and also other devices, like parallel ports (SUNW,bpp anyone?) > > But the timing is entirely a concept of the hardware devices. It seems > like it would be easier to just add a growable buffer, and then setup a > timer in each device that reads from the buffer. I don't see why timing is device specific. The mechanisms for setting the speed are device specific, but the throttling should not be. You may need to augment the char driver API to support outgoing throttling. I'd also like to request that this feature be disabled by default. As I've mentined several times before qemu is not cycle accurate, so any attempt to do "accurate" timing is completely arbitrary. In practice I'd expect any throttling is probably going to have to be fairly coarse grained because the emulated cpu speed is extremely variable/irregular, and you're limited by host timer resolution. Paul
Re: [Qemu-devel] high resolution timer question
Blue Swirl wrote: On 12/10/07, Robert Reif <[EMAIL PROTECTED]> wrote: Writing data to a serial port on the sparc emulation happens immediately. I would like to throttle the write speed to match the actual baud rate. What's the best way to do this in qemu? Will QEMUTimer work for a 1 millisecond timer? Do you mean that you want the serial port to match the host speed so that for example, at 9600 baud, target would only receive 9600 bits per second? Or do you mean that the emulated CPU should see bits arriving at the same rate that the real CPU would see compared to CPU execution speed? On the positive side, this would fix a bug with serial interrupts arriving too fast which can trigger Linux panics. But this would also complicate the design because currently the devices do not need to emulate any internal buffers. I think the throttling should be done at CharDriver level so that all targets and also other devices, like parallel ports (SUNW,bpp anyone?) But the timing is entirely a concept of the hardware devices. It seems like it would be easier to just add a growable buffer, and then setup a timer in each device that reads from the buffer. Regards, Anthony Liguori can benefit. It should be turned off when talking to real hardware on the host.
Re: [Qemu-devel] high resolution timer question
On 12/10/07, Robert Reif <[EMAIL PROTECTED]> wrote: > Writing data to a serial port on the sparc emulation happens immediately. > I would like to throttle the write speed to match the actual baud rate. > What's the best way to do this in qemu? Will QEMUTimer work for a > 1 millisecond timer? Do you mean that you want the serial port to match the host speed so that for example, at 9600 baud, target would only receive 9600 bits per second? Or do you mean that the emulated CPU should see bits arriving at the same rate that the real CPU would see compared to CPU execution speed? On the positive side, this would fix a bug with serial interrupts arriving too fast which can trigger Linux panics. But this would also complicate the design because currently the devices do not need to emulate any internal buffers. I think the throttling should be done at CharDriver level so that all targets and also other devices, like parallel ports (SUNW,bpp anyone?) can benefit. It should be turned off when talking to real hardware on the host.
RE: [Qemu-devel] high resolution timer question
The usb host controller emulations in qemu (usb-uhci & usb-ohci) use QEMUTimer for 1 millisecond timer. This precise interval is required for generating usb 1.1 frames. I currently implement usb 2.0 host controller emulation for qemu (usb-ehci). It uses QEMUTimer for generating usb 2.0 microframes of 125 microsecond. This resolution worked precisely only after compiling the host kernel with high resolution timers and dynamic ticks. -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Robert Reif Sent: Monday, December 10, 2007 3:00 PM To: qemu-devel@nongnu.org Subject: [Qemu-devel] high resolution timer question Writing data to a serial port on the sparc emulation happens immediately. I would like to throttle the write speed to match the actual baud rate. What's the best way to do this in qemu? Will QEMUTimer work for a 1 millisecond timer?
