* Cheap: RPi Pico boards are currently EUR4, FT232H boards are closer to EUR15
* Available: As of summer '22, FT232H boards and chips are in short supply; Pico boards are still readily available
* Flexible: Any GPIO-capable pins on the pico can be used for programming. This allow for example multiple ice40 parts to be programmed from a single Pico.
## Usage
First, program your RPi Pico using the included binary 'main.u2f'. To do so, disconnect the pico from your computer, press down the bootloader button, then plug the pico back in. The computer should detect it as a memory device. Copy the main.u2f file into the root directory of this memory device. This will program the Pico. Once completed, the pico should restart and present itself as a USB HID device.
To use it with icestorm, the 'iceprog' utility will need to be built from the above fork. Known issues:
* This version of iceprog is hard-coded to use the pico as a programmer; it should have a command-line switch to choose the correct programmer
* SRAM programming mode (-S) is untested
TODO: Suggested wiring diagram
TODO: Permissions
## Version checking
The firmware version can be determined from the bcdDevice field in the USB device descriptor. Known versions are:
| bcdDevice | Version | Description |
| --- | --- | --- |
| 0x0100 | 1.0 | Raw USB test version |
| 0x0200 | 2.0 | Release version |
The command set described in this document describes the version 2.0 format.
## Command set
Commands are sent to the device as [control transfers](https://www-user.tu-chemnitz.de/~heha/hsn/chm/usb.chm/usb4.htm#Control). The bRequest field is used to select the commmand, and any configuration data associated with the command
| MS_DESCRIPTOR | IN | 0xF8 | 0 | 0 | x | Get a Microsoft OS compatible descriptor |
### Set pin directions
This command is used to set pin directions. The first field is a mask of pins to update, and the second is a bitmap of the resulting states. Any pin that has a bit set in the mask will be updated.
This command is used to set pin pullup/pulldown resistors. The first field is a mask of pins to update, the second is the pull-up states, and the third is the pull-down states. Any pin that has a bit set in the mask will be updated.
This command is used to set the value of output pins. The first field is a mask of pins to update, and the second is a bitmap of new output values to apply. Any pin that has a bit set in the mask will be updated.
Data packet format:
| Offset | Length | Description |
| --- | --- | --- |
| 0x00 | 4 | uint32: Pin mask (1=set direction) |
| 0x04 | 4 | uint32: Pin value (1=high, 0=low) |
### Read pin values
This command is used to read the value of all pins. Note that pins which are confgured as outputs will report their current output setting.
Data packet format:
| Offset | Length | Description |
| --- | --- | --- |
| 0x05 | 4 | uint32: Pin values (1=high, 0=low) |
### Set SPI configuration
This command is used to configure the SPI engine.
Data packet format:
| Offset | Length | Description |
| --- | --- | --- |
| 0x00 | 1 | GPIO pin number for SCK |
| 0x01 | 1 | GPIO pin number for CS |
| 0x02 | 1 | GPIO pin number for MOSI |
| 0x03 | 1 | GPIO pin number for MISO |
| 0x04 | 1 | SPI clock frequency, in MHz |
### Transfer SPI data
This command is used to send data over the pins currently configured as the SPI interface. This command performs a full-duplex read/write operation, and stores the read data in a buffer. To retrieve the data read during this operation, issue a read command.
Data packet format:
| Offset | Length | Description |
| --- | --- | --- |
| 0x00 | 1 | 0: don't toggle CS; any other value: toggle CS |
| 0x01 | 4 | Bytes to transfer |
| 0x05 | 1-2040 | SPI data to transfer |
### Get data read during previous SPI transaction
This command is used to retrieve any data transferred during the previous SPI transaction.
Data packet format:
| Offset | Length | Description |
| --- | --- | --- |
| 0x00 | 1-2040 | SPI data to transfer |
### SPI clock out
This command is used to toggle the SPI clock pin, but doesn't transfer any data.
This command is used to read the analog value of analog input pins 0-2. Each value is returned as a uint32_t value representing the reading in microvolts.
Data packet format:
| Offset | Length | Description |
| --- | --- | --- |
| 0x01 | 4 | ADC channel 0 value, in microvolts |
| 0x05 | 4 | ADC channel 1 value, in microvolts |
| 0x09 | 4 | ADC channel 2 value, in microvolts |
### Bootloader
This command is used to put the device in bootloader mode. No data is sent during this
