Vybrid ProcessorsのトピックVYbrid FPU

VYbrid FPU

jackdean — Mon, 11 Aug 2014 04:06:39 GMT

I can't seem to make the FPU in the VYBrid work.

If I enable it, the cpu hangs on the first FPU instruction.

I'm only setting --fpu-VFPv4 in the DS-5 code generation page.

I get code, but the board instantly crashes, and must be power off to reset; the reset button has not effect.

Any clues?

Re: VYbrid FPU

kef2 — Mon, 11 Aug 2014 12:19:24 GMT

Fore some weird reason DS-5 doesn't care about enabling FPU. You need to have something like this in your startup file:

     MRC p15, 0, r0, c1, c1, 2
     ORR r0, r0, #(3<<10)            ; //enable fpu
     MCR p15, 0, r0, c1, c1, 2
     ;//2. Set the CPACR for access to CP10 and CP11:
     MOV r0, #(0xF << 20)
     MCR p15, 0, r0, c1, c0, 2
     ;//3. Set the FPEXC EN bit to enable the FPU:

MOV R3, #0x40000000
VMSR FPEXC, R3

Re: VYbrid FPU

jackdean — Mon, 11 Aug 2014 16:58:50 GMT

Hi Edward,

Thank you for your reply.

I had this:

; CPACR is located at address 0xE000ED88

LDR.W R0, =0xE000ED88

; Read CPACR

LDR R1, [R0]

; Set bits 20-23 to enable CP10 and CP11 coprocessors

ORR R1, R1, #(0xF << 20)

; Write back the modified value to the CPACR

STR R1, [R0]; wait for store to complete

DSB

;reset pipeline now the FPU is enabled

ISB

Which is from ARM. With your suggestion I get this error:

"F:/VYBrid/Whetstone/src/cpu/crt0_armcc.s", line 120: Error: A1854E: Unknown opcode 'VMSR', maybe wrong target CPU?

with

-DTOWER -DARMCC_A5 -I../../../../../src/common -I../../../../../src/drivers/ccm -I../../../../../src/cpu/header/CMSIS -I../../../../../src/cpu/header -I../../../../../src/cpu -I../../../../../src/platforms -I../../../../../src/drivers/ddr -I../../../../../src/drivers/serial -I../../../../../src/drivers/lptmr -I../../../../../src/projects/Whetstone -O0 --cpu=Cortex-A5 --littleend --arm --fpu=vfpv4 -g --diag_suppress=1786

Thank you again.

Re: VYbrid FPU

kef2 — Mon, 11 Aug 2014 17:59:06 GMT

Oh, I have

--cpu=Cortex-A5.neon

and am using Neon features as well.

Re: VYbrid FPU

jackdean — Mon, 11 Aug 2014 18:38:41 GMT

Thank you for your help and input.