The device side firmware uses a range of different clocks. Here is an attempt to document the clocks in use and for what they are used.
- Notes on device side clocks
- Table of Contents
- Slow clock
- Main Oscillator / MAINCK
- PLL clock
- Master Clock MCK, Processor Clock PCK, USB clock UDPCK
- Peripheral clocks
- 1 kHz RTC: TickCount functions
- Occasional PWM timer
- Occasional TC0+TC1 / CountUS functions
- Occasional TC0+TC1+TC2 SSP_CLK from FPGA / CountSspClk functions
- Occasional TC0+TC1 / Ticks functions
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~32kHz internal RC clock
Can be between 22 and 42 kHz
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cf PMC_MOR register
16 MHz, based on external Xtal
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cf PMC_PLLR register
96 MHz (MAINCK * 12 / 2)
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cf common_arm/clocks.c
cf PMC_MCKR and PMC_SCER registers
- MCK starts with RC slow clock (22 to 42 kHz).
- Then MCK configured from PLL: 48 MHz (PLL / 2)
cf bootrom.c:
PCK can be disabled to enter idle mode, but on Proxmark3 it's always on, so PCK is also 48 MHz.
USB need to be clocked at 48 MHz from the PLL, so PLL / 2 (cf CKGR_PLLR).
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cf bootrom.c:
Distribute MCK/PCK? clock to Parallel I/O controller, ADC, SPI, Synchronous Serial controller, PWM controller, USB.
cf appmain.c
Activate PCK0 pin as clock output, based on PLL / 4 = 24 MHz, for the FPGA.
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cf armsrc/ticks.c
cf PMC_MCFR and RTTC_RTMR registers for configuration, RTTC_RTVR register for reading value.
Characteristics:
- 1 kHz, 32b (49 days), if used with 16b: 65s
- Configured at boot (or TIA) with
StartTickCount() - Time events with
GetTickCount()/GetTickCountDeltaDelta(), see example - Coarse, based on the ~32kHz RC slow clock with some adjustment factor computed by TIA
- Maybe 2.5% error, can increase if temperature conditions change and no TIA is recomputed
- If TimingIntervalAcquisition() is called later, StartTickCount() is called again and RTC is reset
Usage:
uint32_t ti = GetTickCount();
...do stuff...
uint32_t delta = GetTickCountDelta(ti);
Current usages:
- cheap random for nonces, e.g.
prng_successor(GetTickCount(), 32) - rough timing of some operations, only for informative purposes
- timeouts
- USB connection speed measure
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void SpinDelayUs(int us)void SpinDelay(int ms)based on SpinDelayUsvoid SpinDelayUsPrecision(int us)
Busy wait based on 46.875 kHz PWM Channel 0
- 21.3 us precision and maximum 1.39 s
- Precision variant: 0.7 us precision and maximum 43 ms
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cf armsrc/ticks.c
About 1 us precision
void StartCountUS(void)uint32_t RAMFUNC GetCountUS(void)
Use two chained timers TC0 and TC1. TC0 runs at 1.5 MHz and TC1 is clocked when TC0 reaches 0xC000.
Maximal value: 0x7fffffff = 2147 s
Can't be used at the same time as CountSspClk or Ticks functions.
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cf armsrc/ticks.c
About 1 cycle of 13.56 MHz? precision
void StartCountSspClk(void)void ResetSspClk(void)uint32_t RAMFUNC GetCountSspClk(void)uint32_t RAMFUNC GetCountSspClkDelta(uint32_t start)<= TODO could be used more often
Use two chained timers TC0 and TC1. TC0 runs at SSP_CLK from FPGA (13.56 MHz?) and TC1 is clocked when TC0 loops.
Usage:
- for iso14443 commands to count field cycles
- Also usable with FPGA in LF mode ?? cf
armsrc/legicrfsim.cSSP Clock is clocked by the FPGA at 212 kHz (sub-carrier frequency)
Can't be used at the same time as CountUS or Ticks functions.
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cf armsrc/ticks.c
1.5 MHz
void StartTicks(void)uint32_t GetTicks(void)<= TODO why no GetTicksDelta ?void WaitTicks(uint32_t ticks)void WaitUS(uint32_t us)void WaitMS(uint32_t ms)void StopTicks(void)<= TODO why a stop for this timer and not for CountUS / CountSspClk ?
Use two chained timers TC0 and TC1. TC0 runs at 1.5 MHz and TC1 is clocked when TC0 loops.
Maximal value: 0xffffffff = 2863 s (but don't use high value with WaitTicks else you'll trigger WDT)
Usage:
- Timer for bitbanging, or LF stuff when you need a very precise timer
Can't be used at the same time as CountUS or CountSspClk functions.