From c33aafcd5c5ceca7391813b530462668331d54c9 Mon Sep 17 00:00:00 2001 From: Aidan MacDonald Date: Thu, 14 Nov 2024 14:47:45 +0000 Subject: [PATCH] arm: add ARMv7-M version of ARMv6 mixer code GCC cannot compile the existing assembly here on ARMv7-M, claiming impossible constraints. It is actually possible to compile if the input arguments (addresses and sizes) are first moved to a high register so as not to conflict with the use of r0-r7 in ldm/stm -- this is exactly what GCC does for ARMv6, but it won't do it on ARMv7-M for some reason. We can get a result similar to the ARMv6 code by manually moving the inputs into temporaries, but the generated code is a actually a bit smaller on ARMv7-M if the r0-r7 block is shifted up to r3-r10. This only works since ARMv7-M supports the 32-bit Thumb encoding -- 16-bit Thumb can't represent an ldm/stm instruction of this type. It's worth #ifdef'ing the code because although the ARMv7-M version works on ARMv6 too, it spills a lot of registers on the stack even though register use is mostly similar. Change-Id: I9bc8b5c76e198aecfd0a0e7a2158b1c00f82c4df --- firmware/asm/arm/pcm-mixer-armv6.c | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+) diff --git a/firmware/asm/arm/pcm-mixer-armv6.c b/firmware/asm/arm/pcm-mixer-armv6.c index 9da5b40ef1..c1334bcd6a 100644 --- a/firmware/asm/arm/pcm-mixer-armv6.c +++ b/firmware/asm/arm/pcm-mixer-armv6.c @@ -78,6 +78,27 @@ static FORCE_INLINE void write_samples(void *out, if (LIKELY(amp == MIX_AMP_UNITY)) { /* Channel is unity amplitude */ +#if defined(CPU_ARM_MICRO) && ARCH_VERSION >= 7 + asm volatile ( + "ands r4, %2, #0x1f \n" + "beq 2f \n" + "1: \n" + "ldr r3, [%1], #4 \n" + "subs r4, r4, #4 \n" + "str r3, [%0], #4 \n" + "bne 1b \n" + "bics %2, %2, #0x1f \n" + "beq 3f \n" + "2: \n" + "ldmia %1!, { r3-r10 } \n" + "subs %2, %2, #32 \n" + "stmia %0!, { r3-r10 } \n" + "bhi 2b \n" + "3: \n" + : "+lr"(out), "+lr"(src), "+r"(size) + : + : "r3", "r4", "r5", "r6", "r7", "r8", "r9", "r10"); +#else asm volatile ( "ands r1, %2, #0x1f \n" "beq 2f \n" @@ -97,6 +118,7 @@ static FORCE_INLINE void write_samples(void *out, : "+r"(out), "+r"(src), "+r"(size) : : "r0", "r1", "r2", "r3", "r4", "r5", "r6", "r7"); +#endif } else {