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    PPI和DPPI的功能及应用说明

PPI和DPPI的功能及应用说明 2024-01-16 Gao Jun, Nordic Semiconductor

PPI,英文全称是Programmable Peripheral Interconnect;DPPI,英文全称是Distributed Programmable Peripheral Interconnect。PPI是nRF52系列芯片的一个外设,从nRF53系列开始,使用DPPI代替了PPI。

1. 什么是PPI和DPPI?

  • PPI,英文全称是Programmable Peripheral Interconnect;
  • DPPI,英文全称是Distributed Programmable Peripheral Interconnect。

PPI是nRF52系列芯片的一个外设,从nRF53系列开始,使用DPPI代替了PPI。PPI和DPPI的设计目的是相同的,都提供了一种机制,让某个外设的事件可以触发另一个外设的任务,让一个外设直接控制另一个外设成为可能,从而减少了CPU的参与,和DMA有异曲同工之效。比如,我们可以用timer定时器去触发一个ADC采样,这样就不需要CPU执行指令去触发采样了。所谓编程(Programmable),就是指可以通过配置寄存器,将不同外设的事件和任务建立关联。

2. 什么是事件(event)和任务(task)?

说到PPI和DPPI就绕不过事件和任务。那么这个事件和任务又是什么呢?学习过MCU的同学都知道外设(Peripheral)都会有与之对应的控制寄存器和状态寄存器,而我们Nordic的控制寄存器和状态寄存器的设计有些与众不同。我们将控制寄存器的控制逻辑做了细分,将每一个控制逻辑都具体成了一个任务,一个任务就对应一个任务寄存器。同样,将状态寄存器的状态也做了细分,将每一个不同的状态都具体成了一个事件,一个事件就对应一个事件寄存器。

以UARTE模块为例,它的task和event寄存器如下:

Register Offset Description
TASKS_STARTRX 0x000 Start UART receiver
TASKS_STOPRX 0x004 Stop UART receiver
TASKS_STARTTX 0x008 Start UART transmitter
TASKS_STOPTX 0x00C Stop UART transmitter
TASKS_FLUSHRX 0x02C Flush RX FIFO into RX buffer
...
EVENTS_CTS 0x100 CTS is activated (set low). Clear To Send.
EVENTS_NCTS 0x104 CTS is deactivated (set high). Not Clear To Send.
EVENTS_RXDRDY 0x108 Data received in RXD (potentially not yet transferred to Data RAM)
EVENTS_ENDRX 0x110 Receive buffer is filled up
EVENTS_TXDRDY 0x11C Data sent from TXD
EVENTS_ENDTX 0x120 Last TX byte transmitted
EVENTS_ERROR 0x124 Error detected
EVENTS_RXTO 0x144 Receiver timeout
EVENTS_RXSTARTED 0x14C UART receiver has started
EVENTS_TXSTARTED 0x150 UART transmitter has started
EVENTS_TXSTOPPED 0x158 Transmitter stopped

3. 什么是通道(Channel)?

通道可以想象成一个管道,管道的输入端关联event寄存器,管道的输出端关联task寄存器。管道上有开关,当开关被打开时(channel enable),event寄存器如果有信号,就能触发管道另一头的task寄存器,从而触发task寄存器对应的控制逻辑。PPI和DPPI的主要区别是:通道与event寄存器和task寄存器建立关联的机制不同。PPI的机制决定了一个通道只能关联一个event和一个task,即只能一对一(一个event触发一个task),利用fork机制可以做到一对二(一个event触发两个task)。DPPI的一个通道可以和多个task和event做关联,能做到多对多(多个event触发多个task)。另外,通道还有自己的管理机制,还可以分组管理。PPI和DPPI的通道管理机制是相同的。

4.PPI框图

PPI框图

  • EEP是event end point的缩写;TEP是task end point的缩写。每一个通道都有自己的EEP和TEP寄存器。

  • CH[i].EEP是一个配置寄存器,负责存储event register 地址,使外设的event与通道i(CH[i])建立关联。

  • CH[i].TEP也是一个配置寄存器,负责存储task register 地址,使外设的task与通道i (CH[i])建立关联。

  • PPI允许一个event或task和多个通道建立关联。即不同的通道里可以写入同一个event或task地址。但一个通道只能和一个event建立关联,因为某个通道i对应的CH[i].EEP里只能写入一个地址。Task比较特殊,因为有FORK[i].TEP的存在,所以CH[i].TEP和FORK[i].TEP可以写入两个不同的task register地址,实现一对二。FORK功能只存在于PPI,DPPI没有FORK功能。

  • 接入同一个通道的event和task可以形成通路,为event触发task逻辑创造条件。

  • CHEN, CHENSET, CHENCLR和CHG[m]则是用来管理这些通道(enable and disable the channels)是否使能。

  • 0-19通道可以任意配置;20-31通道的task和event是固定的,不能配置。

Instance Channel Number of channels
PPI 0-19 20
PPI (fixed) 20-31 12
Channel EEP TEP
20 TIMER0->EVENTS_COMPARE[0] RADIO->TASKS_TXEN
21 TIMER0->EVENTS_COMPARE[0] RADIO->TASKS_RXEN
22 TIMER0->EVENTS_COMPARE[1] RADIO->TASKS_DISABLE
23 RADIO->EVENTS_BCMATCH AAR->TASKS_START
24 RADIO->EVENTS_READY CCM->TASKS_KSGEN
25 RADIO->EVENTS_ADDRESS CCM->TASKS_CRYPT
26 RADIO->EVENTS_ADDRESS TIMER0->TASKS_CAPTURE[1]
27 RADIO->EVENTS_END TIMER0->TASKS_CAPTURE[2]
28 RTC0->EVENTS_COMPARE[0] RADIO->TASKS_TXEN
29 RTC0->EVENTS_COMPARE[0] RADIO->TASKS_RXEN
30 RTC0->EVENTS_COMPARE[0] TIMER0->TASKS_CLEAR
31 RTC0->EVENTS_COMPARE[0] TIMER0->TASKS_START
  • PPI的EEP和TEP寄存器:

CH[n].EEP (n=0..19)

Address offset: 0x510 + (n × 0x8)
Channel n event endpoint

EEP channel information

ID Access Field ValueID Value Description
A RW EEP Pointer to event register. Accepts only addresses to registers from the Event group.

CH[n].TEP (n=0..19)

Address offset: 0x514 + (n × 0x8)
Channel n task endpoint

TEP channel information

ID Access Field ValueID Value Description
A RW TEP Pointer to task register. Accepts only addresses to registers from the Task group.

FORK[n].TEP (n=0..19, 20..31)

Address offset: 0x910 + (n × 0x4)
Channel n task endpoint

FORK channel information

ID Access Field ValueID Value Description
A RW TEP Pointer to task register.

5.DPPI框图

DPPI框图

  • 所有外围设备都含有一系列的任务订阅寄存器和事件发布寄存器(每个task寄存器对应一个订阅( subscribe)寄存器;每个event寄存器对应一个发布(publish)寄存器)。(订阅和发布寄存器取代了PPI中EEP和TEP寄存器的功能)
  • 发布和订阅的对象是通道(channel)
  • 同一个通道可以被不同的事件发布,被不同的任务订阅,达到多对多的效果。
  • 以下是ADC模块的task,event,subscribe task,publish event寄存器。
Register Offset Description
TASKS_START 0x000 Start the ADC and prepare the result buffer in RAM
TASKS_SAMPLE 0x004 Take one ADC sample, if scan is enabled all channels are sampled
TASKS_STOP 0x008 Stop the ADC and terminate any ongoing conversion
TASKS_CALIBRATEOFFSET 0x00C Starts offset auto-calibration
SUBSCRIBE_START 0x080 Subscribe configuration for task START
SUBSCRIBE_SAMPLE 0x084 Subscribe configuration for task SAMPLE
SUBSCRIBE_STOP 0x088 Subscribe configuration for task STOP
SUBSCRIBE_CALIBRATEOFFSET 0x08C Subscribe configuration for task CALIBRATEOFFSET
EVENTS_STARTED 0x100 The ADC has started
EVENTS_END 0x104 The ADC has filled up the Result buffer
EVENTS_DONE 0x108 A conversion task has been completed. Depending on the mode, multiple conversions might be needed for a result to be transferred to RAM.
EVENTS_RESULTDONE 0x10C A result is ready to get transferred to RAM
EVENTS_CALIBRATEDONE 0x110 Calibration is complete
EVENTS_STOPPED 0x114 The ADC has stopped
EVENTS_CH[n].LIMITH 0x118 Last results is equal or above CH[n].LIMIT.HIGH
EVENTS_CH[n].LIMITL 0x11C Last results is equal or below CH[n].LIMIT.LOW
PUBLISH_STARTED 0x180 Publish configuration for event STARTED
PUBLISH_END 0x184 Publish configuration for event END
PUBLISH_DONE 0x188 Publish configuration for event DONE
PUBLISH_RESULTDONE 0x18C Publish configuration for event RESULTDONE
PUBLISH_CALIBRATEDONE 0x190 Publish configuration for event CALIBRATEDONE
PUBLISH_STOPPED 0x194 Publish configuration for event STOPPED
PUBLISH_CH[n].LIMITH 0x198 Publish configuration for event CH[n].LIMITH
PUBLISH_CH[n].LIMITL 0x19C Publish configuration for event CH[n].LIMITL

6. 通道管理和组(group)

  • PPI和DPPI对通道的管理方式基本相同

  • 通过通道管理寄存器,每一个通道可以被单独使能或是禁用,相关寄存器如下:

CHENSET

Address offset: 0x504
Channel enable set register

Note: Read: Reads value of CH[i] field in CHEN register

CHENSET

ID Access Field ValueID Value Description
A-f RW CH[i] (i=0..31) Channel i enable set register. Writing '0' has no effect.
Disabled 0 Read: channel disabled
Enabled 1 Read: channel enabled
Set 1 Write: Enable channel

CHENCLR

Address offset: 0x508
Channel enable clear register

Note: Read: Reads value of CH[i] field in CHEN register

CHENCLR

ID Access Field ValueID Value Description
A-f RW CH[i] (i=0..31) Channel i enable set register. Writing '0' has no effect.
Disabled 0 Read: channel disabled
Enabled 1 Read: channel enabled
Set 1 Write: Enable channel
  • CHENSET和CHENCLR寄存器用于设置通道,如果要读取通道的状态,需要读取CHEN寄存器。

CHEN

Address offset: 0x500
Channel enable register

CHEN

ID Access Field ValueID Value Description
A-f RW CH[i] (i=0..31) Channel i enable set register. Writing '0' has no effect.
Disabled 0 Read: channel disabled
Enabled 1 Read: channel enabled
Set 1 Write: Enable channel
  • 不同的通道可以分配到一个组里。一共支持6个组。CHG[n](n=0..5)寄存器有32bit,每一个bit位对应一个通道号,如果相应的bit位被置“1”,那么这个通道就被分配到了当前的组中。

CHG[n] (n=0..5)

Address offset: 0x800 + (n x 0x4)
Channel group n

Note: Writes to this register are ignored if either SUBSCRIBE_CHG[n].EN or SUBSCRIBE_CHG[n].DIS are enabled

CHEN

ID Access Field ValueID Value Description
A-f RW CH[i] (i=0..31) Include or exclude channel i
Excluded 0 Exclude
Included 1 Include
  • 每一个组都有两个task寄存器,一个task(TASKS_CHG[n].EN)控制组使能,另一个task (TASKS_CHG[n].DIS)控制组禁用。有了task,那么它们也可以通过PPI/DPPI的机制,被别的event触发。当TASKS_CHG[n].EN被触发,同一组内所有的通道被使能;当TASKS_CHG[n].DIS被触发,同一组内所有的通道被禁用。

TASKS_CHG[n].EN (n=0..5)

Address offset: 0x000 + (n x 0x8)
Enable channel group n

TASK ENABLE

ID Access Field ValueID Value Description
A W EN Enable channel group n
Trigger 1 Trigger task

TASKS_CHG[n].DIS (n=0..5)

Address offset: 0x004 + (n x 0x8)
Disable channel group n

TASK DISABLE

ID Access Field ValueID Value Description
A W DIS Disable channel group n
Trigger 1 Trigger task

7. PPI和DPPI的驱动资源及使用流程

  • PPI 驱动位于modules\hal\nordic\nrfx\drivers\src\nrfx_ppi.c;DPPI驱动位于modules\hal\nordic\nrfx\drivers\src\nrfx_dppi.c
  • 为了兼容PPI和DPPI,还设计了辅助层(Helper layer:modules\hal\nordic\nrfx\helpers\nrfx_gppi.h) 提供 PPI 和 DPPI 驱动的通用功能。辅助层直接调用PPI和DPPI的驱动程序,使用辅助层时,需要考虑到PPI 和 DPPI 接口在应用时的明显差异。
  • PPI和DPPI的使用流程相同,都很简单:

1)分配(申请)通道

2)对于PPI,通道两端分别关联task和event;对于DPPI,task(Subscribe)和event(Publish)端关联通道

3)使能通道

8. PPI和DPPI配置代码示例

1)Timer COMPARE0 EVENT产生的时候触发ADC采样。按下button1启动timer,端口输出低电平,按下button2停止timer,端口输出高电平。下面列举了PPI多通道,以及FORK使用的配置代码。

status = nrfx_ppi_channel_alloc(&m_timer_saadc_ppi_channel);
NRFX_ASSERT(status == NRFX_SUCCESS);
status = nrfx_ppi_channel_assign(m_timer_saadc_ppi_channel, 
            nrfx_timer_event_address_get(&m_sample_timer, NRF_TIMER_EVENT_COMPARE0),
            nrf_saadc_task_address_get(NRF_SAADC, NRF_SAADC_TASK_SAMPLE));
NRFX_ASSERT(status == NRFX_SUCCESS);

//button1 start timer and output low
status = nrfx_ppi_channel_alloc(&m_button0_timer_ppi_channel);
NRFX_ASSERT(status == NRFX_SUCCESS);
status = nrfx_ppi_channel_assign(m_button0_timer_ppi_channel, 
              nrfx_gpiote_in_event_addr_get(INPUT_PIN_0),
              nrf_timer_task_address_get(m_sample_timer.p_reg, NRF_TIMER_TASK_START));
NRFX_ASSERT(status == NRFX_SUCCESS);
status = nrfx_ppi_channel_fork_assign(m_button0_timer_ppi_channel,
              nrfx_gpiote_clr_task_addr_get(OUTPUT_PIN));
NRFX_ASSERT(status == NRFX_SUCCESS); 

//button2 stop timer and output high
  status = nrfx_ppi_channel_alloc(&m_button1_timer_ppi_channel);
NRFX_ASSERT(status == NRFX_SUCCESS);
status = nrfx_ppi_channel_assign(m_button1_timer_ppi_channel, 
              nrfx_gpiote_in_event_addr_get(INPUT_PIN_1),
              nrf_timer_task_address_get(m_sample_timer.p_reg, NRF_TIMER_TASK_STOP));
NRFX_ASSERT(status == NRFX_SUCCESS);
status = nrfx_ppi_channel_fork_assign(m_button1_timer_ppi_channel,
              nrfx_gpiote_set_task_addr_get(OUTPUT_PIN));
NRFX_ASSERT(status == NRFX_SUCCESS); 

2)Timer COMPARE0 EVENT产生的时候触发ADC采样。按下button1启动timer,端口输出低电平,按下button2停止timer,端口输出高电平。下面列举了DPPI多通道使用的配置代码。

status = nrfx_dppi_channel_alloc(&m_timer_saadc_dppi_channel);
NRFX_ASSERT(status == NRFX_SUCCESS);
nrf_timer_publish_set(m_sample_timer.p_reg, NRF_TIMER_EVENT_COMPARE0,
    m_timer_saadc_dppi_channel);
nrf_saadc_subscribe_set(NRF_SAADC, NRF_SAADC_TASK_SAMPLE, m_timer_saadc_dppi_channel);

//button1 start timer and output low
status = nrfx_dppi_channel_alloc(&m_button0_timer_dppi_channel);
NRFX_ASSERT(status == NRFX_SUCCESS);
nrf_gpiote_publish_set(NRF_GPIOTE, nrfx_gpiote_in_event_get(INPUT_PIN_0),
    m_button0_timer_dppi_channel);
nrf_gpiote_subscribe_set(NRF_GPIOTE,nrfx_gpiote_clr_task_addr_get(OUTPUT_PIN),m_button0_timer_dppi_channel);			
NRFX_ASSERT(status == NRFX_SUCCESS);
nrf_timer_subscribe_set(m_sample_timer.p_reg, NRF_TIMER_TASK_START, m_button0_timer_dppi_channel);
NRFX_ASSERT(status == NRFX_SUCCESS);

//button2 stop timer and output high
status = nrfx_dppi_channel_alloc(&m_button1_timer_dppi_channel);
NRFX_ASSERT(status == NRFX_SUCCESS);
nrf_gpiote_publish_set(NRF_GPIOTE, nrfx_gpiote_in_event_get(INPUT_PIN_1),
    m_button1_timer_dppi_channel);
nrf_gpiote_subscribe_set(NRF_GPIOTE,nrfx_gpiote_set_task_addr_get(OUTPUT_PIN),m_button1_timer_dppi_channel);			
NRFX_ASSERT(status == NRFX_SUCCESS);
nrf_timer_subscribe_set(m_sample_timer.p_reg, NRF_TIMER_TASK_STOP, m_button1_timer_dppi_channel);
NRFX_ASSERT(status == NRFX_SUCCESS);

3)组(group)的使用代码示例。使用timer,gpiote,dppi输出固定周期的波形。只有在COMPARE2 EVENT发生的时候,将输出电平置高;在COMPARE3 EVENT发生的时候,将输出电平置低。第一次产生COMPARE1 EVENT的时候,触发了timer clear的task, timer重新开始计数,那么COMPARE0 EVENT就不会发生了。 COMPARE1 EVENT还触发了group disable task。那么,下一个COMPARE1 EVENT就不会触发timer clear task了,因为这个channel被disable了。 COMPARE1 EVENT发生后, COMPARE0 EVENT会接着发生。在COMPARE0 EVENT产生的中断处理里面,通过group的控制函数,又将channel使能了。那么,COMPARE1 EVENT,又能触发了timer clear task,循环上面的动作。输出波形如下:

输出波形

  • Timer设置:
#define PERIOD       (20*16000)   //compare0  (duty=25%)
#define SHORT_PERIOD (10*16000)   //compare1 (duty=50%)
#define OFFSET       1            //compare2
#define PULSE_WIDTH  (5*16000)    //compare3
/*
//2 3 1 2 3 1 0 2 3 1 2 3 1 0
  __   __       __   __       __   __       __   __   
 _| |__| |______| |__| |______| |__| |______| |__| |______
  2 3  1 3   1  0 3  1 3   1  0 3  1 3   1  0 3  1 3  1  0
       2        2    2        2    2        2    2
*/
static void timer_init(void)
{
    nrfx_timer_config_t timer_config = NRFX_TIMER_DEFAULT_CONFIG;
    timer_config.frequency = NRF_TIMER_FREQ_125kHz;
    timer_config.bit_width = NRF_TIMER_BIT_WIDTH_32;
    nrfx_timer_init(&timer, &timer_config, timer_handler);
    nrfx_timer_compare(&timer, NRF_TIMER_CC_CHANNEL0, PERIOD, true);
    nrf_timer_shorts_enable(timer.p_reg, NRF_TIMER_SHORT_COMPARE0_CLEAR_MASK);
    nrfx_timer_compare(&timer, NRF_TIMER_CC_CHANNEL1, SHORT_PERIOD, true);
    nrfx_timer_compare(&timer, NRF_TIMER_CC_CHANNEL2, OFFSET, false);
    nrfx_timer_compare(&timer, NRF_TIMER_CC_CHANNEL3, OFFSET + PULSE_WIDTH, false);

    IRQ_CONNECT(TIMER0_IRQn, NRFX_TIMER_DEFAULT_CONFIG_IRQ_PRIORITY - 1,
        nrfx_timer_0_irq_handler, NULL, 0);

    configure_one_time_clear();
    nrfx_timer_enable(&timer);

}
//NRF_TIMER_EVENT_COMPARE1触发中断,每次会发生;
//触发task,则是一次不允许,一次允许。触发task的时候,会清timer
//timer清了COMPARE0就不会发生了。下次,task不触发时,compare0就会发生,然后使能task触发。

static void timer_handler(nrf_timer_event_t event_type, void *p_context)
{
  if (event_type == NRF_TIMER_EVENT_COMPARE0) {
      printk("0");
      //group里面只有一个通道的情况下,下面两个函数的功能是等价的。
      nrfx_dppi_group_enable(group_ch);
      //nrfx_dppi_channel_enable(channel_ch);
  }
  if (event_type == NRF_TIMER_EVENT_COMPARE1) {
      printk("1");
  }
}
  • DPPI分配组,分配通道,关联通道配置COMPARE1 EVENT触发timer clear,加入组,配置COMPARE1 EVENT触发group disable task。然后使能通道。
static void configure_one_time_clear(void)
{
  nrfx_dppi_group_alloc(&group_ch);
  nrfx_dppi_channel_alloc(&channel_ch);
  nrf_timer_publish_set(timer.p_reg, NRF_TIMER_EVENT_COMPARE1, channel_ch);
  nrf_timer_subscribe_set(timer.p_reg, NRF_TIMER_TASK_CLEAR, channel_ch);
  nrfx_dppi_channel_include_in_group(channel_ch, group_ch);

  //影响下次event触发task,把通道disable了。
  nrf_dppi_subscribe_set(NRF_DPPIC, nrf_dppi_group_disable_task_get(group_ch), channel_ch);
  nrfx_dppi_channel_enable(channel_ch);
}
  • DPPI分配通道,配置COMPARE2 EVENT触发output ‘H’,使能通道;DPPI分配通道,配置COMPARE3 EVENT触发output ‘L’,使能通道。
nrfx_gpiote_out_init(OUTPUT_PIN, &out_config);
nrfx_gpiote_out_task_enable(OUTPUT_PIN);

uint8_t channel;
nrfx_dppi_channel_alloc(&channel);
nrf_timer_publish_set(timer.p_reg, NRF_TIMER_EVENT_COMPARE2, channel);
nrf_gpiote_subscribe_set(
        NRF_GPIOTE,
        nrfx_gpiote_set_task_get(OUTPUT_PIN),
        channel);
nrfx_dppi_channel_enable(channel);

nrfx_dppi_channel_alloc(&channel);
nrf_timer_publish_set(timer.p_reg, NRF_TIMER_EVENT_COMPARE3, channel);
nrf_gpiote_subscribe_set(
        NRF_GPIOTE,
        nrfx_gpiote_clr_task_get(OUTPUT_PIN),
        channel);
nrfx_dppi_channel_enable(channel);

上述完整代码可在百度网盘下载

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