trigger_settings.md

There are settings for the trigger, which controls when the system should respond to incoming signals and starting taking data (for example, only when it sees beam pulses, or only when it receives a pulse from the accelerator trigger telling it beam is coming soon). Set the trigger with the cf00003c register. Here is an explanation from Matthew on how the adc_trigger.vhd file works:

• The adc_fd[3..0] inputs are supposed to be the fast-detect signals from the ADC chips. This is a really nice way to get triggers out of them because you can program the threshold and hysteresis parameters directly in the ADC, and they are asserted many clock cycles before the data appears on the serial link. They should be set up so that if they are '1' then there is a pulse in that channel.
• ext_trig is an external trigger source which can come from anywhere.
• inhibit is not being used anymore. The logic that used to use it is commented out.
• mask is the trigger mask which defines which trigger algorithm is to be ignored.
• pres is not used anymore, but it used to provide a way to prescale high-rate triggers.

constant trigger_lookup : trigger_lookup_t := (
--     trigger     adc_fd
    "00000000",   -- 0000
    "00000001",   -- 0001
    "00000001",   -- 0010
    "00000011",   -- 0011
    "00000001",   -- 0100
    "00000011",   -- 0101
    "00000011",   -- 0110
    "01010111",   -- 0111
    "00000001",   -- 1000
    "00100011",   -- 1001
    "00000011",   -- 1010
    "00100111",   -- 1011
    "00000011",   -- 1100
    "00100111",   -- 1101
    "10000111",   -- 1110
    "00001111"    -- 1111
  );

In the stack of 4 scintillators with each going to one ADC channel:

• The low 4 bits of the algorithm count whether there is 0, 1, 2, or 3 FD inputs in coincidence (the order doesn't matter).
• Bit 5 seems to indicate when there are hits in the 'top' and 'bottom' scintillators, but not in either middle one.
• Bits 4 and 6 together both indicate when there are hits in the top three scintillators, but not the bottom one. This detects a muon that stopped in the third scintillator.
• It looks like the logic replaces bit 7 by the external trigger input (so it doesn't matter here)

Here's how you can set the mask:

Mask Setting	Binary	Valid adc_fd signals	Description
0xFF	0b1111,1111	None	Ignores everything
0xFE	0b1111,1110	0001, 0010, 0100, 1000	At least one input has an FD signal high
0xFD	0b1111,1101	0011, 0101, 0110, 1001, 1010, 1100	At least two inputs have FD signals high
0xFB	0b1111,1011	0111, 1011, 1101, 1110	At least three inputs have FD signals high
0xF7	0b1111,0101	1111	All four FD inputs are high
0x7F (default)	0b0111,1111	Ignores adc_fd	External trigger is high (ignores FD signals)
0xEF	0b1110,1111	0111	Stopped particle trigger (hits in top 3 but not bottom)
0x00	0b0000,0000	Anything	Allow any trigger condition

Set the trigger mask by doing in the minicomA window: poke cf00003c <mask setting. The current default is poke cf00003c 0x7f to take input from the external trigger only.

The current adc_fd status can be read from register cf000000, which contains a combination of many status registers. The full register returns:

• fmc228_csr(31 downto 24) & adc_fd_r & fmc228_csr(19 downto 18) & trig_in & trig_busy & lmk_sysref_req & fmc228_csr(14 downto 12) & hmc_ldo & fmc228_csr(10 downto 5) & lmk_status_ld & fmc228_csr(2 downto 0);

Our "adc_fd_r" of interest is bits 23 to 20 of the register, and can be read by doing in the minicomA window: peek cf000000. An example return value of 00030930 (binary 0000_0000_0000_0011_0000_1001_0011_0000) would mean that the adc_fd register is 0b0011, which means either first/second scintillators or third/fourth scintillators have a signal (not sure which actually!)