emUSB-Host has been designed to fit many kinds of embedded design requirements. Several features can be excluded from a build to get a minimal system that can efficiently act as a USB host. In the following section the memory usage of typical 32-bit embedded systems is listed.
Please note that the values shown below are approximate values and features selected can influence the final size. The measurement were made using a project for an ARM Cortex-M4 CPU with size optimization and GCC 7.2.1.
ROM
The following table shows the approximate ROM requirement of emUSB-Host:
| Core Components | ROM |
|---|---|
| emUSB-Host core | 6.7 KByte |
| external HUB support | 3.2 KByte |
| Class Components | ROM |
| HID class support | 6.8 KByte |
| MSD class support | 6.9 KByte + (size of file system) |
| CDC-ACM class support | 5.4 KByte |
| FT232 component support | 3.9 KByte |
| Printer class support | 3.1 KByte |
| MTP class support | 13.2 KByte |
| Vendor class support | 4.0 KByte |
| LAN using ASIX | 7.2 KBytes + embOS/IP |
| LAN using CDC-ECM | 7.8 KBytes + embOS/IP |
| LAN using RNDIS | 8.1 KBytes + embOS/IP |
| CCID class support | 5.4 KBytes |
| On-The-Go support | 0.34 KByte + emUSB-Device |
| Drivers | ROM |
| Driver EHCI | 5 KByte |
| Driver OHCI | 7.6 KByte |
| Driver Synopsys / STM32 | 5 KByte |
| Driver Renesas | 5.3 KByte |
RAM
The following table shows the average RAM requirement of emUSB-Host: *
| Component | RAM |
|---|---|
| emUSB-Host core incl. one driver | 3.8 KByte + (ca. 3 KByte stack for the managing tasks) |
| For each connected generic HID device | 3.0 KByte |
| For each connected CDC ACM device | 4.0 KByte |
| For each connected MSD device | 2.2 KByte |
| For each connected Mouse | 4.6 KByte |
| For each connected Vendor device | 3.5 KByte |
| For each connected external HUB | 2.0 KByte |
| For each connected LAN (ASIX) device | 13.5 KByte |
| For each connected LAN (CDC-ECM) device | 11.1 KByte |
| For each connected LAN (RNDIS) device | 18.1 KByte |
* The actual RAM usage may vary depending on the USB host controller used, the memory architecture of the target, the USB devices connected to emUSB-Host and the type of operations performed with that devices.