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target/arm: Implement dummy versions of M-profile FP-related registers

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The M-profile floating point support has three associated config
registers: FPCAR, FPCCR and FPDSCR. It also makes the registers
CPACR and NSACR have behaviour other than reads-as-zero.
Add support for all of these as simple reads-as-written registers.
We will hook up actual functionality later.

The main complexity here is handling the FPCCR register, which
has a mix of banked and unbanked bits.

Note that we don't share storage with the A-profile
cpu->cp15.nsacr and cpu->cp15.cpacr_el1, though the behaviour
is quite similar, for two reasons:
 * the M profile CPACR is banked between security states
 * it preserves the invariant that M profile uses no state
   inside the cp15 substruct

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20190416125744.27770-4-peter.maydell@linaro.org
This commit is contained in:
Peter Maydell 2019-04-29 17:35:58 +01:00
parent 84d2e3e2ae
commit d33abe82c7
4 changed files with 180 additions and 0 deletions
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5
target/arm/cpu.c
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@ -281,6 +281,11 @@ static void arm_cpu_reset(CPUState *s)
env->v7m.ccr[M_REG_S] |= R_V7M_CCR_UNALIGN_TRP_MASK;
}
if (arm_feature(env, ARM_FEATURE_VFP)) {
env->v7m.fpccr[M_REG_NS] = R_V7M_FPCCR_ASPEN_MASK;
env->v7m.fpccr[M_REG_S] = R_V7M_FPCCR_ASPEN_MASK |
R_V7M_FPCCR_LSPEN_MASK | R_V7M_FPCCR_S_MASK;
}
/* Unlike A/R profile, M profile defines the reset LR value */
env->regs[14] = 0xffffffff;