PRU based frequency measurement

[Hithesh Karanth]

kernel 3.8.x 

Thanks for the effort for addressing this problem in advance.

The following assembler and python files concists of my code to measure frequencies on the respectiver ports P8_15 and P8_16 using PRU0. The only problem being the outout of one of those frequency measured is always fluctuatung by a large margin (does show the actual output sometimes). I agree with the fact that this code can handle frequency measurement at one ports flawlessly I have checked for overflow of memory assigned at the shared ram and I can confirm that the flaw in output is not due to the overflow. 

Any help would be appreseated.

Thank you.

The following code is assembler code I have been using-

.origin 0

#define PRU0_ARM_INTERRUPT 19

#define CONST_PRUCFG         C4

#define CONST_PRUSHAREDRAM   C28

 

#define PRU0_CTRL            0x22000

#define PRU1_CTRL            0x24000

 

#define CTPPR0               0x28

 

#define OWN_RAM              0x000

#define OTHER_RAM            0x020

#define SHARED_RAM           0x100

#define SECOND               200000000      // 2e8 5ns cycles

#define DELAY                  200      // 0.01 s

    

START:

    lbco r0, CONST_PRUCFG, 4, 4          // Enable OCP master port

    clr  r0, r0, 4

    sbco r0, CONST_PRUCFG, 4, 4

    

    mov  r0, SHARED_RAM                  // Set C28 to point to shared RAM

    mov  r1, PRU0_CTRL + CTPPR0

    sbbo r0, r1, 0, 4

    mov  r2.w0, DELAY & 0xFFFF

    mov  r2.w2, DELAY >> 16 

WAITLO:

    qbbc WAITLO, r31.t15

IGNORE:                              // Wait for 50 consecutive readings of 1

    add  r0, r0, 2                     // 3 cycles per loop

    qbgt IGNORE, r0, r2

WAIT1:                                 // Continue counting while input is still 1

    add  r0, r0, 2

    qbbs WAIT1, r31.t15

WAIT2:                                 // Continue counting while input is 0

    add  r0, r0, 2

    qbbc WAIT2, r31.t15                // End count when input goes to 1

    sbco r0, CONST_PRUSHAREDRAM, 0, 4  // Write count to RAM

    MOV R31.b0, PRU0_ARM_INTERRUPT+16   // Send notification to Host for program completion

    mov r0,0

    

WAITLO1:

    qbbc WAITLO1, r31.t14

IGNORE1:                              // Wait for 50 consecutive readings of 1

    add  r0, r0, 2                     // 3 cycles per loop

    qbgt IGNORE1, r0, r2

  

WAIT3:                                 // Continue counting while input is still 1

    add  r0, r0, 2

    qbbs WAIT3, r31.t14

WAIT4:                                 // Continue counting while input is 0

    add  r0, r0, 2

    qbbc WAIT4, r31.t14                // End count when input goes to 1

    sbco r0, CONST_PRUSHAREDRAM,8 , 4  // Write count to RAM

    MOV R31.b0, PRU0_ARM_INTERRUPT+16   // Send notification to Host for program completion

    mov  r0, 0

    jmp  IGNORE