Usbtinyisp

USBTinyISP is a project based on a software USB implementation on the Atmel ATTINY2313 by Dick Streefland, [http://dicks.home.xs4all.nl/index.html ]

USB comes in several speeds, 4 mbps (low speed), 12 mbps (USB 1.1 'full' speed), 480 mbps (USB 2.0 high speed), and recently 5 gbps (USB 3.0)

It runs on low speed USB, and apparently can get away with a simple resonator instead of a crystal for the clocking. The following USB commands are implemented: Enumeration: Reset (SE0 bus signal, D+ and D- both pulled low) Signal low speed back to host (device pulls up D- signal) Bit decoding (using NRZ encoding on the fly)

USB Chapter 9 (identification of USB devices in lower software layers) SetAddress() GetConfiguration() GetDescriptor(string) SetConfiguration()

The actual functionality is implemented with SETUP packets, followed by an IN packet (back to host) and empty OUT packet that needs to be acked as well. Setup packet fields: Request: uint8 wValue: uint16 wIndex: uint16 wLength: uint16

For SPI transfers, Vendor Request In (0x07) can be used. it accepts no more than 4 bytes, that are put in wValue c1c0,wIndex c3c2). There is no chip-select, and no way of controlling other peripherals on the SPI bus (reset). There are not enough IO buffers on the board to convert the 5V rails of the TINY2313 to the target level (VDDext = 3V3). To work around this, I want to use a simple diode.

First investigation is outputting a clock and bytes, and verify this on the scope. The SPI clock coming out of my tinyISP it looks very distorted - it looks almost like the normal slow clock of ca 10 kHz was interrupted by a 40 kHz clock.

I first need to verify if the binary in the chip is the same as intended.