X-Git-Url: https://git.gag.com/?p=fw%2Faltos;a=blobdiff_plain;f=doc%2Fmicropeak.xsl;h=aa1adaef9f57a2bc64d34033c301abe3662dd3a5;hp=284d0fb04a359ff11e7b3f865d9dee5b7f841f78;hb=6fa1ec0dbf2a4eda8d061c67b3779b83b88f29f0;hpb=ceea0e75ac42acac4a20bf88f34bb93fd2768f4c
diff --git a/doc/micropeak.xsl b/doc/micropeak.xsl
index 284d0fb0..aa1adaef 100644
--- a/doc/micropeak.xsl
+++ b/doc/micropeak.xsl
@@ -37,6 +37,13 @@
Updates for version 1.0 release.
+
+ 1.1
+ 12 December 2012
+
+ Add comments about EEPROM storage format and programming jig.
+
+
@@ -223,10 +230,10 @@ NAR #88757, TRA #12200
with the negative battery terminal.
- Shipping restrictions prevent us from including a CR1025
- battery with MicroPeak. Many stores carry CR1025 batteries as
- they are commonly used in small electronic devices such as
- flash lights.
+ Shipping restrictions may prevent us from including a CR1025
+ battery with MicroPeak. If so, many stores carry CR1025
+ batteries as they are commonly used in small electronic
+ devices such as flash lights.
@@ -272,6 +279,118 @@ NAR #88757, TRA #12200
serve to further protect the switch from launch forces.
+
+ On-board data storage
+
+ The ATtiny85 has 512 bytes of non-volatile storage, separate
+ from the code storage memory. The MicroPeak firmware uses this
+ to store information about the last completed
+ flight. Barometric measurements from the ground before launch
+ and at apogee are stored, and used at power-on to compute the
+ height of the last flight.
+
+
+ In addition to the data used to present the height of the last
+ flight, MicroPeak also stores barometric information sampled
+ at regular intervals during the flight. This information can
+ be extracted from MicroPeak through any AVR programming
+ tool.
+
+
+ MicroPeak EEPROM Data Storage
+
+
+
+
+
+
+ Address
+ Size (bytes)
+ Description
+
+
+
+
+ 0x000
+ 4
+ Average ground pressure (Pa)
+
+
+ 0x004
+ 4
+ Minimum flight pressure (Pa)
+
+
+ 0x008
+ 2
+ Number of in-flight samples
+
+
+ 0x00a ⦠0x1fe
+ 2
+ Instantaneous flight pressure (Pa) low 16 bits
+
+
+
+
+
+ All EEPROM data are stored least-significant byte first. The
+ instantaneous flight pressure data are stored without the
+ upper 16 bits of data. The upper bits can be reconstructed
+ from the previous sample, assuming that pressure doesn't
+ change by more more than 32kPa in a single sample
+ interval. Note that this pressure data is not
+ filtered in any way, while both the recorded ground and apogee
+ pressure values are, so you shouldn't expect the minimum
+ instantaneous pressure value to match the recorded minimum
+ pressure value exactly.
+
+
+ MicroPeak samples pressure every 96ms, but stores only every
+ other sample in the EEPROM. This provides for 251 pressure
+ samples at 192ms intervals, or 48.192s of storage. The clock
+ used for these samples is a factory calibrated RC circuit
+ built into the ATtiny85 and is accurate only to within ±10% at
+ 25°C. So, you can count on the pressure data being accurate,
+ but speed or acceleration data computed from this will be
+ limited by the accuracy of this clock.
+
+
+
+ MicroPeak Programming Interface
+
+ MicroPeak exposes a standard 6-pin AVR programming interface,
+ but not using the usual 2x3 array of pins on 0.1"
+ centers. Instead, there is a single row of tiny 0.60mm Ã
+ 0.85mm pads on 1.20mm centers exposed near the edge of the
+ circuit board. We couldn't find any connector that was
+ small enough to include on the circuit board.
+
+
+ In lieu of an actual connector, the easiest way to connect to
+ the bare pads is through a set of Pogo pins. These
+ spring-loaded contacts are designed to connect in precisely
+ this way. We've designed a programming jig, the MicroPeak
+ Pogo Pin board which provides a standard AVR interface on one
+ end and a recessed slot for MicroPeak to align the board with
+ the Pogo Pins.
+
+
+ The MicroPeak Pogo Pin board is not a complete AVR programmer,
+ it is an interface board that provides a 3.3V regulated power
+ supply to run the MicroPeak via USB and a standard 6-pin AVR
+ programming interface with the usual 2x3 grid of pins on 0.1"
+ centers. This can be connected to any AVR programming
+ dongle.
+
+
+ The AVR programming interface cannot run faster than ¼ of the
+ AVR CPU clock frequency. Because MicroPeak runs at 250kHz to
+ save power, you must configure your AVR programming system to
+ clock the AVR programming interface at no faster than
+ 62.5kHz, or a clock period of 32µS.
+
+