Re: [Qemu-devel] [PATCH v3 18/20] hw/intc/arm_gicv3: Add IRQ handling CPU interface registers

[Shannon Zhao <zhaoshenglong@huawei.com>]

On 2016/6/14 22:38, Peter Maydell wrote:
> Add the CPU interface registers which deal with acknowledging
> and dismissing interrupts.
> 
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Shannon Zhao <shannon.zhao@linaro.org>

> ---
>  hw/intc/arm_gicv3_cpuif.c | 437 ++++++++++++++++++++++++++++++++++++++++++++++
>  hw/intc/gicv3_internal.h  |   5 +
>  trace-events              |   7 +
>  3 files changed, 449 insertions(+)
> 
> diff --git a/hw/intc/arm_gicv3_cpuif.c b/hw/intc/arm_gicv3_cpuif.c
> index a368dbb..5b2972e 100644
> --- a/hw/intc/arm_gicv3_cpuif.c
> +++ b/hw/intc/arm_gicv3_cpuif.c
> @@ -219,6 +219,297 @@ static void icc_pmr_write(CPUARMState *env, const ARMCPRegInfo *ri,
>      gicv3_cpuif_update(cs);
>  }
>  
> +static void icc_activate_irq(GICv3CPUState *cs, int irq)
> +{
> +    /* Move the interrupt from the Pending state to Active, and update
> +     * the Active Priority Registers
> +     */
> +    uint32_t mask = icc_gprio_mask(cs, cs->hppi.grp);
> +    int prio = cs->hppi.prio & mask;
> +    int aprbit = prio >> 1;
> +    int regno = aprbit / 32;
> +    int regbit = aprbit % 32;
> +
> +    cs->icc_apr[cs->hppi.grp][regno] |= (1 << regbit);
> +
> +    if (irq < GIC_INTERNAL) {
> +        cs->gicr_iactiver0 = deposit32(cs->gicr_iactiver0, irq, 1, 1);
> +        cs->gicr_ipendr0 = deposit32(cs->gicr_ipendr0, irq, 1, 0);
> +        gicv3_redist_update(cs);
> +    } else {
> +        gicv3_gicd_active_set(cs->gic, irq);
> +        gicv3_gicd_pending_clear(cs->gic, irq);
> +        gicv3_update(cs->gic, irq, 1);
> +    }
> +}
> +
> +static uint64_t icc_hppir0_value(GICv3CPUState *cs, CPUARMState *env)
> +{
> +    /* Return the highest priority pending interrupt register value
> +     * for group 0.
> +     */
> +    bool irq_is_secure;
> +
> +    if (cs->hppi.prio == 0xff) {
> +        return INTID_SPURIOUS;
> +    }
> +
> +    /* Check whether we can return the interrupt or if we should return
> +     * a special identifier, as per the CheckGroup0ForSpecialIdentifiers
> +     * pseudocode. (We can simplify a little because for us ICC_SRE_EL1.RM
> +     * is always zero.)
> +     */
> +    irq_is_secure = (!(cs->gic->gicd_ctlr & GICD_CTLR_DS) &&
> +                     (cs->hppi.grp != GICV3_G1NS));
> +
> +    if (cs->hppi.grp != GICV3_G0 && !arm_is_el3_or_mon(env)) {
> +        return INTID_SPURIOUS;
> +    }
> +    if (irq_is_secure && !arm_is_secure(env)) {
> +        /* Secure interrupts not visible to Nonsecure */
> +        return INTID_SPURIOUS;
> +    }
> +
> +    if (cs->hppi.grp != GICV3_G0) {
> +        /* Indicate to EL3 that there's a Group 1 interrupt for the other
> +         * state pending.
> +         */
> +        return irq_is_secure ? INTID_SECURE : INTID_NONSECURE;
> +    }
> +
> +    return cs->hppi.irq;
> +}
> +
> +static uint64_t icc_hppir1_value(GICv3CPUState *cs, CPUARMState *env)
> +{
> +    /* Return the highest priority pending interrupt register value
> +     * for group 1.
> +     */
> +    bool irq_is_secure;
> +
> +    if (cs->hppi.prio == 0xff) {
> +        return INTID_SPURIOUS;
> +    }
> +
> +    /* Check whether we can return the interrupt or if we should return
> +     * a special identifier, as per the CheckGroup1ForSpecialIdentifiers
> +     * pseudocode. (We can simplify a little because for us ICC_SRE_EL1.RM
> +     * is always zero.)
> +     */
> +    irq_is_secure = (!(cs->gic->gicd_ctlr & GICD_CTLR_DS) &&
> +                     (cs->hppi.grp != GICV3_G1NS));
> +
> +    if (cs->hppi.grp == GICV3_G0) {
> +        /* Group 0 interrupts not visible via HPPIR1 */
> +        return INTID_SPURIOUS;
> +    }
> +    if (irq_is_secure) {
> +        if (!arm_is_secure(env)) {
> +            /* Secure interrupts not visible in Non-secure */
> +            return INTID_SPURIOUS;
> +        }
> +    } else if (!arm_is_el3_or_mon(env) && arm_is_secure(env)) {
> +        /* Group 1 non-secure interrupts not visible in Secure EL1 */
> +        return INTID_SPURIOUS;
> +    }
> +
> +    return cs->hppi.irq;
> +}
> +
> +static uint64_t icc_iar0_read(CPUARMState *env, const ARMCPRegInfo *ri)
> +{
> +    GICv3CPUState *cs = icc_cs_from_env(env);
> +    uint64_t intid;
> +
> +    if (!icc_hppi_can_preempt(cs)) {
> +        intid = INTID_SPURIOUS;
> +    } else {
> +        intid = icc_hppir0_value(cs, env);
> +    }
> +
> +    if (!(intid >= INTID_SECURE && intid <= INTID_SPURIOUS)) {
> +        icc_activate_irq(cs, intid);
> +    }
> +
> +    trace_gicv3_icc_iar0_read(gicv3_redist_affid(cs), intid);
> +    return intid;
> +}
> +
> +static uint64_t icc_iar1_read(CPUARMState *env, const ARMCPRegInfo *ri)
> +{
> +    GICv3CPUState *cs = icc_cs_from_env(env);
> +    uint64_t intid;
> +
> +    if (!icc_hppi_can_preempt(cs)) {
> +        intid = INTID_SPURIOUS;
> +    } else {
> +        intid = icc_hppir1_value(cs, env);
> +    }
> +
> +    if (!(intid >= INTID_SECURE && intid <= INTID_SPURIOUS)) {
> +        icc_activate_irq(cs, intid);
> +    }
> +
> +    trace_gicv3_icc_iar1_read(gicv3_redist_affid(cs), intid);
> +    return intid;
> +}
> +
> +static void icc_drop_prio(GICv3CPUState *cs, int grp)
> +{
> +    /* Drop the priority of the currently active interrupt in
> +     * the specified group.
> +     *
> +     * Note that we can guarantee (because of the requirement to nest
> +     * ICC_IAR reads [which activate an interrupt and raise priority]
> +     * with ICC_EOIR writes [which drop the priority for the interrupt])
> +     * that the interrupt we're being called for is the highest priority
> +     * active interrupt, meaning that it has the lowest set bit in the
> +     * APR registers.
> +     *
> +     * If the guest does not honour the ordering constraints then the
> +     * behaviour of the GIC is UNPREDICTABLE, which for us means that
> +     * the values of the APR registers might become incorrect and the
> +     * running priority will be wrong, so interrupts that should preempt
> +     * might not do so, and interrupts that should not preempt might do so.
> +     */
> +    int i;
> +
> +    for (i = 0; i < ARRAY_SIZE(cs->icc_apr[grp]); i++) {
> +        uint64_t *papr = &cs->icc_apr[grp][i];
> +
> +        if (!*papr) {
> +            continue;
> +        }
> +        /* Clear the lowest set bit */
> +        *papr &= *papr - 1;
> +        break;
> +    }
> +
> +    /* running priority change means we need an update for this cpu i/f */
> +    gicv3_cpuif_update(cs);
> +}
> +
> +static bool icc_eoi_split(CPUARMState *env, GICv3CPUState *cs)
> +{
> +    /* Return true if we should split priority drop and interrupt
> +     * deactivation, ie whether the relevant EOIMode bit is set.
> +     */
> +    if (arm_is_el3_or_mon(env)) {
> +        return cs->icc_ctlr_el3 & ICC_CTLR_EL3_EOIMODE_EL3;
> +    }
> +    if (arm_is_secure_below_el3(env)) {
> +        return cs->icc_ctlr_el1[GICV3_S] & ICC_CTLR_EL1_EOIMODE;
> +    } else {
> +        return cs->icc_ctlr_el1[GICV3_NS] & ICC_CTLR_EL1_EOIMODE;
> +    }
> +}
> +
> +static int icc_highest_active_group(GICv3CPUState *cs)
> +{
> +    /* Return the group with the highest priority active interrupt.
> +     * We can do this by just comparing the APRs to see which one
> +     * has the lowest set bit.
> +     * (If more than one group is active at the same priority then
> +     * we're in UNPREDICTABLE territory.)
> +     */
> +    int i;
> +
> +    for (i = 0; i < ARRAY_SIZE(cs->icc_apr[0]); i++) {
> +        int g0ctz = ctz32(cs->icc_apr[GICV3_G0][i]);
> +        int g1ctz = ctz32(cs->icc_apr[GICV3_G1][i]);
> +        int g1nsctz = ctz32(cs->icc_apr[GICV3_G1NS][i]);
> +
> +        if (g1nsctz < g0ctz && g1nsctz < g1ctz) {
> +            return GICV3_G1NS;
> +        }
> +        if (g1ctz < g0ctz) {
> +            return GICV3_G1;
> +        }
> +        if (g0ctz < 32) {
> +            return GICV3_G0;
> +        }
> +    }
> +    /* No set active bits? UNPREDICTABLE; return -1 so the caller
> +     * ignores the spurious EOI attempt.
> +     */
> +    return -1;
> +}
> +
> +static void icc_deactivate_irq(GICv3CPUState *cs, int irq)
> +{
> +    if (irq < GIC_INTERNAL) {
> +        cs->gicr_iactiver0 = deposit32(cs->gicr_iactiver0, irq, 1, 0);
> +        gicv3_redist_update(cs);
> +    } else {
> +        gicv3_gicd_active_clear(cs->gic, irq);
> +        gicv3_update(cs->gic, irq, 1);
> +    }
> +}
> +
> +static void icc_eoir_write(CPUARMState *env, const ARMCPRegInfo *ri,
> +                           uint64_t value)
> +{
> +    /* End of Interrupt */
> +    GICv3CPUState *cs = icc_cs_from_env(env);
> +    int irq = value & 0xffffff;
> +    int grp;
> +
> +    trace_gicv3_icc_eoir_write(gicv3_redist_affid(cs), value);
> +
> +    if (ri->crm == 8) {
> +        /* EOIR0 */
> +        grp = GICV3_G0;
> +    } else {
> +        /* EOIR1 */
> +        if (arm_is_secure(env)) {
> +            grp = GICV3_G1;
> +        } else {
> +            grp = GICV3_G1NS;
> +        }
> +    }
> +
> +    if (irq >= cs->gic->num_irq) {
> +        /* This handles two cases:
> +         * 1. If software writes the ID of a spurious interrupt [ie 1020-1023]
> +         * to the GICC_EOIR, the GIC ignores that write.
> +         * 2. If software writes the number of a non-existent interrupt
> +         * this must be a subcase of "value written does not match the last
> +         * valid interrupt value read from the Interrupt Acknowledge
> +         * register" and so this is UNPREDICTABLE. We choose to ignore it.
> +         */
> +        return;
> +    }
> +
> +    if (icc_highest_active_group(cs) != grp) {
> +        return;
> +    }
> +
> +    icc_drop_prio(cs, grp);
> +
> +    if (!icc_eoi_split(env, cs)) {
> +        /* Priority drop and deactivate not split: deactivate irq now */
> +        icc_deactivate_irq(cs, irq);
> +    }
> +}
> +
> +static uint64_t icc_hppir0_read(CPUARMState *env, const ARMCPRegInfo *ri)
> +{
> +    GICv3CPUState *cs = icc_cs_from_env(env);
> +    uint64_t value = icc_hppir0_value(cs, env);
> +
> +    trace_gicv3_icc_hppir0_read(gicv3_redist_affid(cs), value);
> +    return value;
> +}
> +
> +static uint64_t icc_hppir1_read(CPUARMState *env, const ARMCPRegInfo *ri)
> +{
> +    GICv3CPUState *cs = icc_cs_from_env(env);
> +    uint64_t value = icc_hppir1_value(cs, env);
> +
> +    trace_gicv3_icc_hppir1_read(gicv3_redist_affid(cs), value);
> +    return value;
> +}
> +
>  static uint64_t icc_bpr_read(CPUARMState *env, const ARMCPRegInfo *ri)
>  {
>      GICv3CPUState *cs = icc_cs_from_env(env);
> @@ -331,6 +622,104 @@ static void icc_ap_write(CPUARMState *env, const ARMCPRegInfo *ri,
>      gicv3_cpuif_update(cs);
>  }
>  
> +static void icc_dir_write(CPUARMState *env, const ARMCPRegInfo *ri,
> +                          uint64_t value)
> +{
> +    /* Deactivate interrupt */
> +    GICv3CPUState *cs = icc_cs_from_env(env);
> +    int irq = value & 0xffffff;
> +    bool irq_is_secure, single_sec_state, irq_is_grp0;
> +    bool route_fiq_to_el3, route_irq_to_el3, route_fiq_to_el2, route_irq_to_el2;
> +
> +    trace_gicv3_icc_dir_write(gicv3_redist_affid(cs), value);
> +
> +    if (irq >= cs->gic->num_irq) {
> +        /* Also catches special interrupt numbers and LPIs */
> +        return;
> +    }
> +
> +    if (!icc_eoi_split(env, cs)) {
> +        return;
> +    }
> +
> +    int grp = gicv3_irq_group(cs->gic, cs, irq);
> +
> +    single_sec_state = cs->gic->gicd_ctlr & GICD_CTLR_DS;
> +    irq_is_secure = !single_sec_state && (grp != GICV3_G1NS);
> +    irq_is_grp0 = grp == GICV3_G0;
> +
> +    /* Check whether we're allowed to deactivate this interrupt based
> +     * on its group and the current CPU state.
> +     * These checks are laid out to correspond to the spec's pseudocode.
> +     */
> +    route_fiq_to_el3 = env->cp15.scr_el3 & SCR_FIQ;
> +    route_irq_to_el3 = env->cp15.scr_el3 & SCR_IRQ;
> +    /* No need to include !IsSecure in route_*_to_el2 as it's only
> +     * tested in cases where we know !IsSecure is true.
> +     */
> +    route_fiq_to_el2 = env->cp15.hcr_el2 & HCR_FMO;
> +    route_irq_to_el2 = env->cp15.hcr_el2 & HCR_FMO;
> +
> +    switch (arm_current_el(env)) {
> +    case 3:
> +        break;
> +    case 2:
> +        if (single_sec_state && irq_is_grp0 && !route_fiq_to_el3) {
> +            break;
> +        }
> +        if (!irq_is_secure && !irq_is_grp0 && !route_irq_to_el3) {
> +            break;
> +        }
> +        return;
> +    case 1:
> +        if (!arm_is_secure_below_el3(env)) {
> +            if (single_sec_state && irq_is_grp0 &&
> +                !route_fiq_to_el3 && !route_fiq_to_el2) {
> +                break;
> +            }
> +            if (!irq_is_secure && !irq_is_grp0 &&
> +                !route_irq_to_el3 && !route_irq_to_el2) {
> +                break;
> +            }
> +        } else {
> +            if (irq_is_grp0 && !route_fiq_to_el3) {
> +                break;
> +            }
> +            if (!irq_is_grp0 &&
> +                (!irq_is_secure || !single_sec_state) &&
> +                !route_irq_to_el3) {
> +                break;
> +            }
> +        }
> +        return;
> +    default:
> +        g_assert_not_reached();
> +    }
> +
> +    icc_deactivate_irq(cs, irq);
> +}
> +
> +static uint64_t icc_rpr_read(CPUARMState *env, const ARMCPRegInfo *ri)
> +{
> +    GICv3CPUState *cs = icc_cs_from_env(env);
> +    int prio = icc_highest_active_prio(cs);
> +
> +    if (arm_feature(env, ARM_FEATURE_EL3) &&
> +        !arm_is_secure(env) && (env->cp15.scr_el3 & SCR_FIQ)) {
> +        /* NS GIC access and Group 0 is inaccessible to NS */
> +        if (prio & 0x80) {
> +            /* NS mustn't see priorities in the Secure half of the range */
> +            prio = 0;
> +        } else if (prio != 0xff) {
> +            /* Non-idle priority: show the Non-secure view of it */
> +            prio = (prio << 1) & 0xff;
> +        }
> +    }
> +
> +    trace_gicv3_icc_rpr_read(gicv3_redist_affid(cs), prio);
> +    return prio;
> +}
> +
>  static void icc_generate_sgi(CPUARMState *env, GICv3CPUState *cs,
>                               uint64_t value, int grp, bool ns)
>  {
> @@ -698,6 +1087,24 @@ static const ARMCPRegInfo gicv3_cpuif_reginfo[] = {
>         */
>        .resetfn = icc_reset,
>      },
> +    { .name = "ICC_IAR0_EL1", .state = ARM_CP_STATE_BOTH,
> +      .opc0 = 3, .opc1 = 0, .crn = 12, .crm = 8, .opc2 = 0,
> +      .type = ARM_CP_IO | ARM_CP_NO_RAW,
> +      .access = PL1_R, .accessfn = gicv3_fiq_access,
> +      .readfn = icc_iar0_read,
> +    },
> +    { .name = "ICC_EOIR0_EL1", .state = ARM_CP_STATE_BOTH,
> +      .opc0 = 3, .opc1 = 0, .crn = 12, .crm = 8, .opc2 = 1,
> +      .type = ARM_CP_IO | ARM_CP_NO_RAW,
> +      .access = PL1_W, .accessfn = gicv3_fiq_access,
> +      .writefn = icc_eoir_write,
> +    },
> +    { .name = "ICC_HPPIR0_EL1", .state = ARM_CP_STATE_BOTH,
> +      .opc0 = 3, .opc1 = 0, .crn = 12, .crm = 8, .opc2 = 2,
> +      .type = ARM_CP_IO | ARM_CP_NO_RAW,
> +      .access = PL1_R, .accessfn = gicv3_fiq_access,
> +      .readfn = icc_hppir0_read,
> +    },
>      { .name = "ICC_BPR0_EL1", .state = ARM_CP_STATE_BOTH,
>        .opc0 = 3, .opc1 = 0, .crn = 12, .crm = 8, .opc2 = 3,
>        .type = ARM_CP_IO | ARM_CP_NO_RAW,
> @@ -762,6 +1169,18 @@ static const ARMCPRegInfo gicv3_cpuif_reginfo[] = {
>        .readfn = icc_ap_read,
>        .writefn = icc_ap_write,
>      },
> +    { .name = "ICC_DIR_EL1", .state = ARM_CP_STATE_BOTH,
> +      .opc0 = 3, .opc1 = 0, .crn = 12, .crm = 11, .opc2 = 1,
> +      .type = ARM_CP_IO | ARM_CP_NO_RAW,
> +      .access = PL1_W, .accessfn = gicv3_irqfiq_access,
> +      .writefn = icc_dir_write,
> +    },
> +    { .name = "ICC_RPR_EL1", .state = ARM_CP_STATE_BOTH,
> +      .opc0 = 3, .opc1 = 0, .crn = 12, .crm = 11, .opc2 = 3,
> +      .type = ARM_CP_IO | ARM_CP_NO_RAW,
> +      .access = PL1_R, .accessfn = gicv3_irqfiq_access,
> +      .readfn = icc_rpr_read,
> +    },
>      { .name = "ICC_SGI1R_EL1", .state = ARM_CP_STATE_AA64,
>        .opc0 = 3, .opc1 = 0, .crn = 12, .crm = 11, .opc2 = 5,
>        .type = ARM_CP_IO | ARM_CP_NO_RAW,
> @@ -798,6 +1217,24 @@ static const ARMCPRegInfo gicv3_cpuif_reginfo[] = {
>        .access = PL1_W, .accessfn = gicv3_irqfiq_access,
>        .writefn = icc_sgi0r_write,
>      },
> +    { .name = "ICC_IAR1_EL1", .state = ARM_CP_STATE_BOTH,
> +      .opc0 = 3, .opc1 = 0, .crn = 12, .crm = 12, .opc2 = 0,
> +      .type = ARM_CP_IO | ARM_CP_NO_RAW,
> +      .access = PL1_R, .accessfn = gicv3_irq_access,
> +      .readfn = icc_iar1_read,
> +    },
> +    { .name = "ICC_EOIR1_EL1", .state = ARM_CP_STATE_BOTH,
> +      .opc0 = 3, .opc1 = 0, .crn = 12, .crm = 12, .opc2 = 1,
> +      .type = ARM_CP_IO | ARM_CP_NO_RAW,
> +      .access = PL1_W, .accessfn = gicv3_irq_access,
> +      .writefn = icc_eoir_write,
> +    },
> +    { .name = "ICC_HPPIR1_EL1", .state = ARM_CP_STATE_BOTH,
> +      .opc0 = 3, .opc1 = 0, .crn = 12, .crm = 12, .opc2 = 2,
> +      .type = ARM_CP_IO | ARM_CP_NO_RAW,
> +      .access = PL1_R, .accessfn = gicv3_irq_access,
> +      .readfn = icc_hppir1_read,
> +    },
>      /* This register is banked */
>      { .name = "ICC_BPR1_EL1", .state = ARM_CP_STATE_BOTH,
>        .opc0 = 3, .opc1 = 0, .crn = 12, .crm = 12, .opc2 = 3,
> diff --git a/hw/intc/gicv3_internal.h b/hw/intc/gicv3_internal.h
> index 8261bc0..6ce5d49 100644
> --- a/hw/intc/gicv3_internal.h
> +++ b/hw/intc/gicv3_internal.h
> @@ -159,6 +159,11 @@
>  #define ICC_CTLR_EL3_A3V (1U << 15)
>  #define ICC_CTLR_EL3_NDS (1U << 17)
>  
> +/* Special interrupt IDs */
> +#define INTID_SECURE 1020
> +#define INTID_NONSECURE 1021
> +#define INTID_SPURIOUS 1023
> +
>  /* Functions internal to the emulated GICv3 */
>  
>  /**
> diff --git a/trace-events b/trace-events
> index 0372c5b..8f8ff04 100644
> --- a/trace-events
> +++ b/trace-events
> @@ -2182,6 +2182,13 @@ gicv3_icc_ctlr_el3_write(uint32_t cpu, uint64_t val) "GICv3 ICC_CTLR_EL3 write c
>  gicv3_cpuif_update(uint32_t cpuid, int irq, int grp, int prio) "GICv3 CPU i/f %x HPPI update: irq %d group %d prio %d"
>  gicv3_cpuif_set_irqs(uint32_t cpuid, int fiqlevel, int irqlevel) "GICv3 CPU i/f %x HPPI update: setting FIQ %d IRQ %d"
>  gicv3_icc_generate_sgi(uint32_t cpuid, int irq, int irm, uint32_t aff, uint32_t targetlist) "GICv3 CPU i/f %x generating SGI %d IRM %d target affinity 0x%xxx targetlist 0x%x"
> +gicv3_icc_iar0_read(uint32_t cpu, uint64_t val) "GICv3 ICC_IAR0 read cpu %x value 0x%" PRIx64
> +gicv3_icc_iar1_read(uint32_t cpu, uint64_t val) "GICv3 ICC_IAR1 read cpu %x value 0x%" PRIx64
> +gicv3_icc_eoir_write(uint32_t cpu, uint64_t val) "GICv3 ICC_EOIR write cpu %x value 0x%" PRIx64
> +gicv3_icc_hppir0_read(uint32_t cpu, uint64_t val) "GICv3 ICC_HPPIR0 read cpu %x value 0x%" PRIx64
> +gicv3_icc_hppir1_read(uint32_t cpu, uint64_t val) "GICv3 ICC_HPPIR1 read cpu %x value 0x%" PRIx64
> +gicv3_icc_dir_write(uint32_t cpu, uint64_t val) "GICv3 ICC_DIR write cpu %x value 0x%" PRIx64
> +gicv3_icc_rpr_read(uint32_t cpu, uint64_t val) "GICv3 ICC_RPR read cpu %x value 0x%" PRIx64
>  
>  # hw/intc/arm_gicv3_dist.c
>  gicv3_dist_read(uint64_t offset, uint64_t data, unsigned size, bool secure) "GICv3 distributor read: offset 0x%" PRIx64 " data 0x%" PRIx64 " size %u secure %d"
> 

-- 
Shannon