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219 lines
6.5 KiB
Plaintext
219 lines
6.5 KiB
Plaintext
UBB pattern generator
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=====================
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ubb-patgen uses the MMC controller in the Ben Nanonote to send a
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digital pattern on the DATx lines of UBB. All four DATx lines can
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be used. The maximum output rate is 56 MHz, the maximum pattern
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size is 8128 nibbles.
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ubb-patgen can also output a clock of arbitrary duration on the
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CLK signal.
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The frequencies available for the pattern and the clock signal
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range from 41 kHz to 56 MHz. A map can be found here:
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http://downloads.qi-hardware.com/people/werner/ubb/ben-mmc-clk.png
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Frequency list
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--------------
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# ubb-patgen
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shows the available frequencies in ascending order and the
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corresponding MMC clock divider and bus clock tap settings.
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# ubb-patgen -q
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does the same but shows only the frequencies (in Hz) as
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floating-point numbers.
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Frequency selection
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-------------------
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# ubb-patgen -f 17000000
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# ubb-patgen -f 17M
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# ubb-patgen -f 17MHz
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all look for the available frequency closest to 17 MHz and print
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its value in Hz.
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Appending a + limits the search to frequencies greater than or
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equal to the specified value. Similarly, - searches for
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frequencies that don't exceed the specified value. Examples:
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# ubb-patgen -f 10MHz
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9882352.941176
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# ubb-patgen -f 10MHz+
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10500000.000000
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# ubb-patgen -f 15M
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15272727.272727
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# ubb-patgen -f 15M-
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14000000.000000
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Note that this form of invocation only searches the frequency
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table but does not produce any output on UBB.
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ubb-patgen warns if the selected frequency does not match the
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requested frequency, e.g.,
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# ubb-patgen -f 100kHz
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bus clk = 100.962 kHz (+0.96%)
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This warning can be suppressed with the option -q.
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The frequency can also be specified as the cycle time with the
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option -i:
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# ubb-patgen -i 10us
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The meaning of an appended + or - changes here, e.g., 10us+
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selects a slower clock (producing an interval of at least 10 us).
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Clock output
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------------
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# ubb-patgen -c
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outputs a clock on CLK. The default is 1 MHz and can be changed
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with the option -f.
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ubb-patgen exits and leaves the clock running. To wait for a
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while and clean up on exit, add the delay in seconds, e.g.:
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# ubb-patgen -f 500kHz -c 10
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The delay can be followed by "m", "u", or "n" for the respective
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multiplier. Furthermore, it can end with an optional "s". Note
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that the minimum time ubb-patgen actually spends generating a
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clock will typically be in the order of several milliseconds.
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To stop the MMC bus clock, run
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# ubb-patgen -c 0
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Pattern output
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--------------
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# ubb-patgen 0110
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first sets the DATx lines to 0, then outputs a 1 bit on DAT0 for
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two clock cycles, and returns DAT0 to zero.
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Each digit is a nibble representing the four DATx lines, with DAT0
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having the value 1, DAT1 2, DAT2 4, and DAT3 8.
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The repetition of a nibble can also be expressed by following it
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with the number of repetitions in curly braces, e.g.,
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# ubb-patgen 01{2}0
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The options -f and -q work as usual.
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The clock is normally not output but can be activated with the
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option -C. Note that the clock output is not continuous in this
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case.
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The pattern can be read from a file. All whitespace is ignored
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and so are comments beginning with #:
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# cat <<EOF >pattern-file
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1 # idle state is high
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# send two characters in RS232 format
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0 00010010 1 # "H"
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0 10010110 1 # "i"
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0 10000100 1 # "!"
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0 10110000 1 # CR
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1 # return to idle (high)
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EOF
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# ubb-patgen -f 115.2k pattern-file
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If a file with the same name as a pattern exists, ubb-patgen will
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try to load that file. This can be prevented with the option -p.
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If only some of the DATx lines should be used for pattern output,
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the option -m MASK can be used to leave the unused lines in their
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previous state. MASK is a value in C syntax. Only lines whose bit
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is set are used for pattern output.
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External trigger
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----------------
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ubb-patgen normally sends the pattern immediately. This can be
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delayed by waiting for an external trigger with the option -t.
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# ubb-patgen -t 0 0f0
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configures CLK as an input, waits for it to become zero, and then
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outputs the 010 pattern. If CLK is already zero, ubb-patgen will
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send the pattern immediately.
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Likewise, -t 1 waits for CLK to become 1. -t cannot be used with
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the -C option.
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The trigger can also be a sequence, e.g., -t 01 would first wait
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for CLK to become zero (if it isn't already), then wait for it to
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become one.
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ubb-patgen usually starts the pattern about 2-10 us after the
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trigger, but this can be delayed by other system activity. An
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extra delay can be added with the option -w, e.g.,
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# ubb-patgen -t 0 -w 1s 010
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The trigger signal can be debounced with the option -d, e.g.,
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# ubb-patgen -t 0 -d 100us 0f0
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This accepts the trigger only after it has been zero for at least
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100 microseconds. If the trigger is a sequence, debouncing is
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applied at each step.
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Timeline details
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----------------
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timing.fig illustrates the various steps of pattern generation.
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A PDF of the diagram can be found here:
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http://downloads.qi-hardware.com/people/werner/ubb/patgen/timeline.pdf
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CLK is the clock output if selected with -C. DATx are the data
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lines, with the value of DAT0 shown. TRIG is the trigger input.
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Note that in real life, the TRIG/CLK line can only act either as
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trigger input or as clock output but not as both at the same time.
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The pattern we send is 0110110. We trigger on TRIG being low, with
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a debounce time of nominally about one pattern clock interval, and
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some post-trigger delay.
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After ubb-patgen starts, it first processes the command-line
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options and arguments, then initializes the pins. DATx are set to
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the value of the first pattern. Next, ubb-patgen sets up the MMC
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controller, makes it send a command, receives a pseudo-response,
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and begins sending copies of the first pattern on DATx. These
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copies are necessary to get past the start bit and to make the MMC
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controller drive DATx to known levels. Once this pattern has been
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sent, we switch DATx to GPIO.
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When this is done, ubb-patgen waits for the trigger. In this
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example, we first ignore a glitch and then detect a correct
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trigger value. Note that the effective debounce period is usually
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longer than specified, since other system activity can delay the
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sampling.
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Once ubb-patgen has triggered, it starts the DMA controller and
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thus begins sending the pattern. The first cycle (marked with a
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question mark) is an uncommanded repetition of the first pattern
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(apparently there is a buffer stage in the MMC controller)
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followed by the entire sequence, first to last pattern.
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At the end, several copies of the last pattern may be sent in
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order to reach the transfer size of the DMA controller (32 bytes).
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ubb-patgen then ensures that all data has left the MMC controller,
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switches DATx back to GPIO, and exits.
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