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clarifications and minor changes in slow clock related operations:

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* SpinDelay and SpinDelayUs: now rounding applies instead of truncating
* Document maximum duration of SpinDelay/SpinDelayUs/BUTTON_CLICK/BUTTON_HELD
* Add argument check against max duration in SpinDelay/BUTTON_CLICK/BUTTON_HELD
* Document why these functions don't need to take wrapping into acount as in GetTickCountDelta
* Use >= in the spinning loops
* Clarify StartTickCount calibration operations and use masks AT91C_CKGR_MAINRDY and AT91C_RTTC_RTPRES
This commit is contained in:
Philippe Teuwen 2019-08-06 13:09:48 +02:00
commit 2cbe43f269
3 changed files with 35 additions and 11 deletions
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22
armsrc/ticks.c
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@ -9,12 +9,14 @@
// Timers, Clocks functions used in LF or Legic where you would need detailed time.
//-----------------------------------------------------------------------------
#include "ticks.h"
// attempt at high resolution microsecond timer
// beware: timer counts in 21.3uS increments (1024/48Mhz)
// timer counts in 21.3uS increments (1024/48Mhz), rounding applies
// WARNING: timer can't measure more than 1.39s (21.3uS * 0xffff)
void SpinDelayUs(int us) {
int ticks = (48 * us) >> 10;
int ticks = (48 * us + 512) >> 10;
// Borrow a PWM unit for my real-time clock
// This resets PWMC_CPRDR as well
AT91C_BASE_PWMC->PWMC_ENA = PWM_CHANNEL(0);
// 48 MHz / 1024 gives 46.875 kHz
@ -26,14 +28,19 @@ void SpinDelayUs(int us) {
for (;;) {
uint16_t now = AT91C_BASE_PWMC_CH0->PWMC_CCNTR;
if (now == (uint16_t)(start + ticks))
if (now >= (uint16_t)(start + ticks))
return;
WDT_HIT();
}
}
// WARNING: timer can't measure more than 1.39s (21.3uS * 0xffff)
void SpinDelay(int ms) {
if (ms > 1390) {
Dbprintf(_RED_("Error, SpinDelay called with %i > 1390"), ms);
ms = 1390;
}
// convert to uS and call microsecond delay function
SpinDelayUs(ms * 1000);
}
@ -49,9 +56,10 @@ void SpinDelay(int ms) {
void StartTickCount(void) {
// This timer is based on the slow clock. The slow clock frequency is between 22kHz and 40kHz.
// We can determine the actual slow clock frequency by looking at the Main Clock Frequency Register.
uint16_t mainf = AT91C_BASE_PMC->PMC_MCFR & 0xffff; // = 16 * main clock frequency (16MHz) / slow clock frequency
// set RealTimeCounter divider to count at 1kHz:
AT91C_BASE_RTTC->RTTC_RTMR = AT91C_RTTC_RTTRST | ((256000 + (mainf / 2)) / mainf);
while ((AT91C_BASE_PMC->PMC_MCFR & AT91C_CKGR_MAINRDY) == 0); // Wait for MAINF value to become available...
uint16_t mainf = AT91C_BASE_PMC->PMC_MCFR & AT91C_CKGR_MAINF; // Get # main clocks within 16 slow clocks
// set RealTimeCounter divider to count at 1kHz, should be 32 if RC is exactly at 32kHz:
AT91C_BASE_RTTC->RTTC_RTMR = AT91C_RTTC_RTTRST | ((((16000000 / 1000 * 16) + (mainf / 2)) / mainf) & AT91C_RTTC_RTPRES);
// note: worst case precision is approx 2.5%
}