Re: [Qemu-devel] [PATCH] hw/wom: Implement write-only-memory device

[Blue Swirl]

On Mon, Apr 1, 2013 at 12:00 AM, Peter Maydell <address@hidden> wrote:
> The lack of a write-only-memory device is a gaping hole in QEMU's
> otherwise comprehensive range of device models. This patch implements
> a model of the popular Signetics 25120 9046xN random access WOM.

Awesome!! I made a short clip to show some possible uses of the
device, everybody check it out:
http://youtu.be/IAISUDbjXj0

> ---
>  hw/Makefile.objs |   2 +
>  hw/wom.c         | 127 
> +++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 129 insertions(+)
>  create mode 100644 hw/wom.c
>
> diff --git a/hw/Makefile.objs b/hw/Makefile.objs
> index d0b2ecb..f26b593 100644
> --- a/hw/Makefile.objs
> +++ b/hw/Makefile.objs
> @@ -195,6 +195,8 @@ common-obj-y += bt-hci-csr.o
>  common-obj-y += ps2.o
>  common-obj-y += qdev-properties-system.o
>
> +common-obj-y += wom.o
> +
>  # xen backend driver support
>  common-obj-$(CONFIG_XEN_BACKEND) += xen_backend.o xen_devconfig.o
>  common-obj-$(CONFIG_XEN_BACKEND) += xen_console.o xenfb.o xen_disk.o 
> xen_nic.o
> diff --git a/hw/wom.c b/hw/wom.c
> new file mode 100644
> index 0000000..ff3c66c
> --- /dev/null
> +++ b/hw/wom.c
> @@ -0,0 +1,127 @@
> +//
> +// Signetics 25120 9046xN random access write only memory
> +//
> +// Written by Peter Maydell
> +//
> +// This code is licensed under the Shrove Tuesday Public Licence
> +// You should have received a copy of the STPL along with this code;
> +// if not, see
> +// http://www.chiark.greenend.org.uk/~christi/public/initview/LICENCE
> +//
> +// Datasheet for this chip available here:
> +// 
> http://www2.vmi.edu/Faculty/squirejc/Research/IC_Datasheets/digital_cmos/Write%20Only%20Memory.pdf
> +
> +// TODO : consider adding WOM support to QEMU core memory system
> +// for improved efficiency and symmetry with ROM support
> +
> +#include "hw/sysbus.h"
> +
> +#define WOMSIZE 9046
> +
> +typedef struct wom_state {
> +  SysBusDevice parent_obj;
> +  MemoryRegion iomem;
> +  qemu_irq irq[30];
> +  uint8_t memory[WOMSIZE];
> +  uint32_t numinsertions;
> +} wom_state;
> +
> +#define TYPE_WOM "wom"
> +#define WOM(obj) OBJECT_CHECK(wom_state, (obj), TYPE_WOM)
> +
> +static uint64_t wom_read(void *opaque, hwaddr offset, unsigned size)
> +{
> +  qemu_log_mask(LOG_GUEST_ERROR, "wom_read: attempt to read from write only 
> memory\n");
> +
> +  return 0xdeadbeef;
> +}
> +
> +static void wom_write(void *opaque, hwaddr offset, uint64_t value,
> +                      unsigned size)
> +{
> +  // Most important feature of this device
> +  wom_state *s = (wom_state *)opaque;
> +  assert(offset < WOMSIZE);
> +  s->memory[offset] = value;
> +}
> +
> +static const MemoryRegionOps wom_ops = {
> +  .read = wom_read,
> +  .write = wom_write,
> +  .endianness = DEVICE_NATIVE_ENDIAN,
> +};
> +
> +static void wom_set_chipdestruct(void *opaque, int line, int level)
> +{
> +  // Self-destruct signal
> +  if (0 != level)
> +    {
> +      // We use hw_error to simulate a blown-up chip taking out the rest of 
> the board
> +      hw_error("WOM has self-destructed!\n");
> +    }
> +}
> +
> +static void wom_reset(DeviceState *dev)
> +{
> +  wom_state *s = WOM(dev);
> +  memset(s->memory, 0, WOMSIZE);
> +}
> +
> +static void wom_realize(DeviceState *dev, Error **errp)
> +{
> +  wom_state *s = WOM(dev);
> +  SysBusDevice *sbd = SYS_BUS_DEVICE(dev);
> +
> +  // GPIO input 0 is the self-destruct signal
> +  qdev_init_gpio_in(dev, wom_set_chipdestruct, 1);
> +
> +  // TODO: better model the relation between number of insertions and number 
> of pins to more
> +  // closely track the graph in the datasheet
> +  int numirqs = 30 / (s->numinsertions + 1);
> +  for (int i = 0; i < numirqs; i++)
> +    {
> +      sysbus_init_irq(sbd, &s->irq[i]);
> +    }
> +
> +  memory_region_init_io(&s->iomem, &wom_ops, s, "wom", WOMSIZE);
> +  sysbus_init_mmio(sbd, &s->iomem);
> +}
> +
> +static const VMStateDescription vmstate_wom = {
> +  .name = "wom",
> +  .version_id = 1,
> +  .minimum_version_id = 1,
> +  .fields = (VMStateField[]) {
> +    VMSTATE_UINT8_ARRAY(memory, wom_state, WOMSIZE),
> +    VMSTATE_END_OF_LIST()
> +  }
> +};
> +
> +static Property wom_properties[] = {
> +  DEFINE_PROP_UINT32("num-insertions", wom_state, numinsertions, 0),
> +  DEFINE_PROP_END_OF_LIST(),
> +};
> +
> +static void wom_class_init(ObjectClass *klass, void *data)
> +{
> +  DeviceClass *dc = DEVICE_CLASS(klass);
> +
> +  dc->realize = wom_realize;
> +  dc->props = wom_properties;
> +  dc->vmsd = &vmstate_wom;
> +  dc->reset = wom_reset;
> +}
> +
> +static const TypeInfo wom_info = {
> +  .name = TYPE_WOM,
> +  .parent = TYPE_SYS_BUS_DEVICE,
> +  .instance_size = sizeof(wom_state),
> +  .class_init = wom_class_init,
> +};
> +
> +static void wom_register_types(void)
> +{
> +  type_register_static(&wom_info);
> +}
> +
> +type_init(wom_register_types)
> --
> 1.7.11.4
>
>