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https://github.com/RfidResearchGroup/proxmark3.git
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215 lines
5.9 KiB
Markdown
215 lines
5.9 KiB
Markdown
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# Notes on device side clocks
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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.
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# Table of Contents
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- [Notes on device side clocks](#notes-on-device-side-clocks)
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- [Table of Contents](#table-of-contents)
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- [Units](#units)
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- [Slow clock](#slow-clock)
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- [Main Oscillator / MAINCK](#main-oscillator--mainck)
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- [PLL clock](#pll-clock)
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- [Master Clock MCK, Processor Clock PCK, USB clock UDPCK](#master-clock-mck-processor-clock-pck-usb-clock-udpck)
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- [Peripheral clocks](#peripheral-clocks)
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- [1 kHz RTC: TickCount functions](#1-khz-rtc-tickcount-functions)
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- [Occasional PWM timer](#occasional-pwm-timer)
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- [Occasional TC0+TC1 / CountUS functions](#occasional-tc0tc1--countus-functions)
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- [Occasional TC0+TC1+TC2 SSP\_CLK from FPGA / CountSspClk functions](#occasional-tc0tc1tc2-ssp_clk-from-fpga--countsspclk-functions)
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- [Occasional TC0+TC1 / Ticks functions](#occasional-tc0tc1--ticks-functions)
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## Units
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^[Top](#top)
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Good calculator
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https://www.unitjuggler.com/convert-frequency-from-MHz-to-ns(p).html?val=3.39
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Basic units of time measurment or how long in time is a Hertz?
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```
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1 hertz = 1 second = 1000 milli seconds
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10 Hertz = 1 / 10 = 0,1 = 100 milli seconds
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100 Hertz = 1 / 100 = 0,01 = 10 milli seconds
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1 kHz = 1 / 1000 = 0,001 = 1 milli seconds
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10 kHz = 1 / 10 000 = 0,000 1 = 100 micro seconds
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100 kHz = 1 / 100 000 = 0,000 01 = 10 micro seconds
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1 MHZ = 1 / 1 000 000 = 0,000 001 = 1 micro seconds
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```
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- kHz, Kilo Hertz, 1000 Hertz
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- MHz, Mega Hertz, 1000 000 Hertz
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Basic units of time you will run into in the RFID world.
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```
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13.56 MHz = 1 / 13 560 000 = 73,74 nano seconds = 0,07374 micro seconds
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125 kHz = 1/ 125 000 = 8 micro seconds
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```
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Given these units the following clocks used by Proxmark3 will make more sense.
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Like the SSP Clock running at 3.39 MHz.
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3.39 MHz = 1 / 3 390 000 = 294,98 nano seconds = 0,2949 micro seconds
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1 tick at 3.39 MHz is 294.98 nano seconds.
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## Slow clock
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^[Top](#top)
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~32kHz internal RC clock
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Can be between 22 and 42 kHz
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## Main Oscillator / MAINCK
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^[Top](#top)
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cf `PMC_MOR` register
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16 MHz, based on external Xtal
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## PLL clock
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^[Top](#top)
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cf `PMC_PLLR` register
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96 MHz (MAINCK * 12 / 2)
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## Master Clock MCK, Processor Clock PCK, USB clock UDPCK
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^[Top](#top)
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cf `common_arm/clocks.c`
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cf `PMC_MCKR` and `PMC_SCER` registers
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* MCK starts with RC slow clock (22 to 42 kHz).
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* Then MCK configured from PLL: 48 MHz (PLL / 2)
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cf `bootrom.c`:
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PCK can be disabled to enter idle mode, but on Proxmark3 it's always on, so PCK is also 48 MHz.
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USB need to be clocked at 48 MHz from the PLL, so PLL / 2 (cf `CKGR_PLLR`).
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## Peripheral clocks
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^[Top](#top)
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cf `bootrom.c`:
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Distribute MCK/PCK? clock to Parallel I/O controller, ADC, SPI, Synchronous Serial controller, PWM controller, USB.
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cf `appmain.c`
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Activate PCK0 pin as clock output, based on PLL / 4 = 24 MHz, for the FPGA.
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## 1 kHz RTC: TickCount functions
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^[Top](#top)
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cf `armsrc/ticks.c`
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cf `PMC_MCFR` and `RTTC_RTMR` registers for configuration, `RTTC_RTVR` register for reading value.
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Characteristics:
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* 1 kHz, 32b (49 days), if used with 16b: 65s
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* Configured at boot (or TIA) with `StartTickCount()`
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* Time events with `GetTickCount()`/`GetTickCountDeltaDelta()`, see example
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* Coarse, based on the ~32kHz RC slow clock with some adjustment factor computed by TIA
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* Maybe 2.5% error, can increase if temperature conditions change and no TIA is recomputed
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* If TimingIntervalAcquisition() is called later, StartTickCount() is called again and RTC is reset
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Usage:
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```
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uint32_t ti = GetTickCount();
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...do stuff...
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uint32_t delta = GetTickCountDelta(ti);
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```
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Current usages:
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* cheap random for nonces, e.g. `prng_successor(GetTickCount(), 32)`
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* rough timing of some operations, only for informative purposes
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* timeouts
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* USB connection speed measure
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## Occasional PWM timer
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^[Top](#top)
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* `void SpinDelayUs(int us)`
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* `void SpinDelay(int ms)` based on SpinDelayUs
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* `void SpinDelayUsPrecision(int us)`
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Busy wait based on 46.875 kHz PWM Channel 0
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* 21.3 us precision and maximum 1.39 s
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* *Precision* variant: 0.7 us precision and maximum 43 ms
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## Occasional TC0+TC1 / CountUS functions
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^[Top](#top)
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cf `armsrc/ticks.c`
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About 1 us precision
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* `void StartCountUS(void)`
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* `uint32_t RAMFUNC GetCountUS(void)`
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Use two chained timers TC0 and TC1.
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TC0 runs at 1.5 MHz and TC1 is clocked when TC0 reaches 0xC000.
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Maximal value: 0x7fffffff = 2147 s
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Can't be used at the same time as CountSspClk or Ticks functions.
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## Occasional TC0+TC1+TC2 SSP_CLK from FPGA / CountSspClk functions
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^[Top](#top)
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cf `armsrc/ticks.c`
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About 1 cycle of 13.56 MHz? precision
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* `void StartCountSspClk(void)`
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* `void ResetSspClk(void)`
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* `uint32_t RAMFUNC GetCountSspClk(void)`
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* `uint32_t RAMFUNC GetCountSspClkDelta(uint32_t start)` <= **TODO** could be used more often
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Use two chained timers TC0 and TC1.
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TC0 runs at SSP_CLK from FPGA (13.56 MHz?) and TC1 is clocked when TC0 loops.
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Usage:
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* for iso14443 commands to count field cycles
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* Also usable with FPGA in LF mode ?? cf `armsrc/legicrfsim.c` SSP Clock is clocked by the FPGA at 212 kHz (sub-carrier frequency)
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Can't be used at the same time as CountUS or Ticks functions.
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## Occasional TC0+TC1 / Ticks functions
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^[Top](#top)
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cf `armsrc/ticks.c`
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1.5 MHz
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* `void StartTicks(void)`
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* `uint32_t GetTicks(void)` <= **TODO** why no GetTicksDelta ?
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* `void WaitTicks(uint32_t ticks)`
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* `void WaitUS(uint32_t us)`
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* `void WaitMS(uint32_t ms)`
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* `void StopTicks(void)` <= **TODO** why a stop for this timer and not for CountUS / CountSspClk ?
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Use two chained timers TC0 and TC1.
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TC0 runs at 1.5 MHz and TC1 is clocked when TC0 loops.
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Maximal value: 0xffffffff = 2863 s (but don't use high value with WaitTicks else you'll trigger WDT)
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Usage:
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* Timer for bitbanging, or LF stuff when you need a very precise timer
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Can't be used at the same time as CountUS or CountSspClk functions.
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