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. --- 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