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Medusa functions by providing appropriate power & signal buses to all card slots, allowing external boards to implement I2C, SPI, UART, Analog, PWM functionalities to perform meaningful operations. Medusa receives commands from the Core Avionics over CAN, and is able to transmit data back to the Core Avionics along CAN as well. It is capable of logging all raw readings from installed cards locally, and transmitting only necessary or otherwise processed data back to the avionics.
Medusa functions by providing appropriate power & signal buses to all card slots, allowing external boards to implement I2C, SPI, UART, Analog, PWM functionalities to perform meaningful operations. Medusa receives commands from the Core Avionics over CAN, and is able to transmit data back to the Core Avionics along CAN as well. It is capable of logging all raw readings from installed cards locally, and transmitting only necessary or otherwise processed data back to the avionics.
== Design ==
Medusa is partitioned into five total slots -- three of which are standard slots, and two of which are ''god slots''. Standard slots partition various pins to reduce or eliminate any conflicts among simultaneously installed cards. God Slots provide access to all Teensy pins that are broken out to the slots.
Each card slot is provided: +5V, +3.3V, +VBAT, GND, I2C, SPI with a unique chip select pin, and a card-detect LED.
Each of the standard slots partition a subset of pins and protocols. Each of the standard slots is provided a Hardware Serial line; Slot 1 utilizes Hardware Serial 1, Slot 2 uses Hardware Serial 2, and so on. They also partition a subset of the PWM and ANALOG pins broken out by the Teensy. All Standard slots have '''two''' PWM pins, located on pins 37/38 and 39/40. Each standard slot also has '''four''' ANALOG pins, located on pins 53/54, 55/56, 57/58, and 59/60.
Slot 1 uses PWM 3/4 and ANALOG 5/6/7/8, Slot 2 uses PWM 1/2 and ANALOG 1/2/3/4, while Slot 3 uses PWM 5/6 and ANALOG 9/10/11/12. This is enumerated on the breakout manifest found on the PCB silkscreen.
The God Slots, however, break out all of these pins. That is, the God Slots have access to PWM 1-6 and ANALOG 1-12. The God Slots should only be used under two conditions: one is the necessity for a large number of ANALOG or PWM pins (more than a standard slot provides), and two being the need for four total cards, with the standard three slots being already taken up. In any case, it is critical for slots to be chosen wisely to avoid conflicts between cards.
God Slots also have the option of using Serial -- however, they utilize Software Serial, and only if enabled using the SS jumpers found on the left of each of the slots. Slot 4 uses Analog pins 1 & 12 for Serial, while Slot 5 uses Analog pins 2 & 11.
All cards should include a trace from pin 71 to pin 72 to enable the on-board medusa card-detect LED.
== Schematics ==
All Medusa Schematics, as well as the PCB Layout, can be found below.
<gallery widths=200px heights=200px>
File:Medusa_top.PNG | <center> Top Sheet </center>
File:Medusa_pow.PNG | <center> Power Connector </center>
File:Medusa_can.PNG | <center> CAN Bus </center>
File:Medusa_microsd.PNG | <center> Micro SD </center>
File:Medusa_sslots.PNG | <center> Standard Slots </center>
File:Medusa_gslots.PNG | <center> God Slots </center>
File:Medusa_pcb.PNG | <center> PCB Layout </center>
</gallery>