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Revert "Override wait_ns to provide more accurate implementation" 

This reverts commit f62010d026.
pull/11023/head
Evelyne Donnaes 2019-07-14 18:07:03 +01:00
parent c781b51644
commit 18f8433d3c
1 changed files with 0 additions and 62 deletions
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62
targets/TARGET_NUVOTON/TARGET_M2351/TARGET_M23_NS/wait_ns.c
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/*
* Copyright (c) 2018-2020, Nuvoton Technology Corporation
*
* SPDX-License-Identifier: Apache-2.0
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include "cmsis.h"
#include "platform/mbed_toolchain.h"
#include "platform/mbed_wait_api.h"
/* Override wait_ns to provide more accurate implementation
*
* At high HCLK rate, M2351 cannot provide zero-wait-state flash performance. Besides,
* cache is off for non-secure land (for internal reason). To fix it, borrowing from
* mbed-os/platform/mbed_wait_api_no_rtos.c wait_ns, we locate 'delay_loop_code' from
* flash to SRAM to achieve zero-wait-state performance.
*
* NOTE1: With MPU, RAM is marked non-executable. We must mark RAM executable for
* running 'delay_loop_code' in SRAM.
* NOTE2: Cache is on for secure land. This override is necessary only for non-secure
* land.
*/
// Cortex-M0+, M3, M4 and M23 take 5 cycles per iteration - SUBS = 1, 2xNOP = 2, BCS = 2
#define LOOP_SCALER 5000
MBED_ALIGN(8)
static uint16_t delay_loop_code[] = {
0x1E40, // SUBS R0,R0,#1
0xBF00, // NOP
0xBF00, // NOP
0xD2FB, // BCS .-3 (0x00 would be .+2, so 0xFB = -5 = .-3)
0x4770 // BX LR
};
/* Take the address of the code, set LSB to indicate Thumb, and cast to void() function pointer */
#define delay_loop ((void(*)()) ((uintptr_t) delay_loop_code | 1))
void wait_ns(unsigned int ns)
{
uint32_t cycles_per_us = SystemCoreClock / 1000000;
// Note that this very calculation, plus call overhead, will take multiple
// cycles. Could well be 100ns on its own... So round down here, startup is
// worth at least one loop iteration.
uint32_t count = (cycles_per_us * ns) / LOOP_SCALER;
mbed_mpu_manager_lock_ram_execution();
delay_loop(count);
mbed_mpu_manager_unlock_ram_execution();
}