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###Nitty-gritty

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TL;DR

Nitty-gritty

Footnote

• Is usbhost.h the correct file to modify the pin used for the USB select line?
• Why does the pin definition of select, for the Mega, appear to be pin 53?

I would like to add USB host functionality, to a particular Arduino setup, whilst being able to use an Ethernet/SD (or just SD) shield.

• "Hardwiring in" a different "select" pin number into a header file;
• Adding an argument to the Init() method, or;
• Adding a method to the USB class, such as Usb.DefineSelect().

The latter two options, I could work through, given the time. However, as a quick and dirty hack, where would I hardwire in a change from pin 10 to a pin of my choosing? Does anyone know? Has anyone had to do this?

• Which is the correct file to modify the Arduino pin used for the USB Host slave select (SS) line?

I would like to add USB host functionality, to a particular Arduino setup, whilst, also, being able to use an Ethernet/SD (or just SD) shield.

• "Hardcoding" a different "select" pin number into a header file;
• Adding an argument to the Init() method, or;
• Adding a method to the USB class, such as Usb.DefineSelect().

The latter two options, I could work through, given the time. However, as a quick and dirty hack, where would I hardcode in a change from pin 10 to a pin of my choosing? Does anyone know? Has anyone had to do this?

Looking at thetypedef SPi< Pb5, Pb3, Pb4, Pb2 > spi; statement, the last argument appears to be the pin used for select. For the Uno (ATmega328P), in avrpins.h (line 535) Pb2 is P10 (pin 10), so I could substitute Pb2 for some other pin definition, i.e. Pd5 for P5 (pin 5) (line 529 in avrpins.h).

However, what I don't understand is that for the Mega (ATmega2560), in avrpins.h (line 512) Pb0is P53, but P10 is Pb4 (line 466). That doesn't tie up with the fact that Pin 10 is used for both the Uno and Mega boards. Unless I have misinterpreted the typedef.

¹From Arduino USB Host Shield

From Arduino Ethernet Shield V2

Looking at the statement

typedef SPi< Pb5, Pb3, Pb4, Pb2 > spi;

the last argument appears to be the pin used for select. For the Uno (ATmega328P), in avrpins.h (line 535) Pb2 is P10 (pin 10), so I could substitute Pb2 for some other pin definition, i.e. Pd5 for P5 (pin 5) (line 529 in avrpins.h).

However, what I don't understand is that for the statement

typedef SPi< Pb1, Pb2, Pb3, Pb0 > spi;

which deals with the Mega (ATmega2560), in avrpins.h (line 512) Pb0is P53 (pin 53). As Pb4 is actually P10 (pin 10) (line 466), why is Pb0 en lieu of Pb4 used? That doesn't tie up with the fact that Pin 10 is used for both the Uno and Mega boards. It seems to suggest the pin 10 is used on the Uno and pin 53 is used on the Mega. Unless I have misinterpreted the typedef.

¹ For the USB host shield, from Arduino USB Host Shield

The key piece of information here is that pin 10 is used by both the Uno and Mega boards.

For the Ethernet shield, from Arduino Ethernet Shield V2

Here, yet again, the key piece of information here is that pin 10 is used by both the Uno and Mega boards to select the Ethernet.