amc bugfix reading aea3 bitshift

[sgiraz]

What's new

• Fix the bitshift reading of chip_MA730 (aka AEA3) on the AMC board

Brief description of the reading

We know that the chip_MA730 has a resolution of 14 bits, so it can count values from 0 to 16383.
We also know that in order to perform a reading we have to send 2 bytes to the clock source.
Finally, from the Datasheet, we know that the first bit of the Byte read is a dummy bit and the last bit of the second Byte is a zero-padded bit.
Let's see how to read the case of maximum value in summary:

Step 0 (initial conditions)

	7	6	5	4	3	2	1	0
Buffer[0]	[dummy]	1	1	1	1	1	1	1
Buffer[1]	1	1	1	1	1	1	1	[zero padded]

	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
position	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-	-

Step 1 (clip Buffer[0] by removing the dummy bit (mask it with 0x7F) and shift it to the left by 7 positions)

	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
position	-	0	1	1	1	1	1	1	1	0	0	0	0	0	0	0

Step 2 (shift Buffer[1] by 1 position to the right, then perform the OR operation with position)

	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
position	-	0	1	1	1	1	1	1	1	1	1	1	1	1	1	1

In the last step, position contains our final 14-bit value ---> 16383.

Furthermore here is the code used to validate the chip_MA730:

#include <iostream>
#include <bitset>
#include <cstdint>

int main(void) {
    uint16_t position = {0};
    uint8_t _databuffer[2] = {0};

    // generate values from 0 to 16383 and try to validate them using the bitshift formula
    
    for(int i = 0; i < 128; i++) {
        
        for(int j = 0; j < 128; j++) {
            
            position = (_databuffer[0] << 7) | (_databuffer[1] >> 1);
            std::cout << std::bitset<8>(_databuffer[0]) << "" 
                      << std::bitset<8>(_databuffer[1]) << " --> "
                      << "position: " << position << std::endl;
            
            _databuffer[1] += 2;
        }
         _databuffer[0] += 1;
    }
    
    return 0;
}

cc @valegagge @ale-git