Neomagic Corporation

Sai K Pothana

Sandeep Kumar

Syed Zaidi

A feature phone has two processors that share a display. The display is attached to an applications processor that has a frame buffer for refreshing the display. A base-band processor also runs programs that generate graphics data that is written to a base-band frame buffer. Updates to the base-band frame buffer are sent through a shared-memory interface to a shared memory, and a shared mailbox is written with the message length, triggering a mailbox-interrupt to the applications processor. The applications processor reads the message from the shared memory and updates a copied frame buffer. An overlay engine uses the copied frame buffer to refresh the display when the base-band processor has the focus, or to refresh a smaller base-band window that covers a portion of the display, leaving the rest of the display area for applications-processor graphics data. Rapid switching between the copied and local frame buffer is possible.

Video overlay buffer mirrored through a shared mailbox between two processors in a feature phone

A feature phone has two processors that share a key pad for user input. The key pad is attached to a base-band processor and sends an interrupt to a user-hardware-interrupt UHI driver running on the base-band processor when the user presses a key. When a hot switch indicates that the local base-band processor has the focus, a key-press event is sent to the local kernel to be sent to programs on the base-band processor. When the hot switch indicates that a remote applications processor has the focus, a message for the event is written through a shared-memory interface to a shared memory on the applications processor. A shared mailbox is written with the message length, triggering a mailbox-interrupt to the applications processor. A virtual UHI driver running on the applications processor reads the event message from the shared memory and passes key-press information to programs on the applications processor.

Virtualization of hardware user-interface using a shared mailbox between two processors in a feature phone

A feature phone has a base-band processor and an applications processor that communicate with each other by emulating an internal Ethernet within the phone. TCP/IP stacks in each processor receive data from high-level applications for transmission to the other processor. Ethernet-emulating drivers are called by the IP layers. An Ethernet-emulating transmit driver writes IP-packet data to a shared memory and sends an interrupt to the other processor, which activates a receive routine that reads the IP packet data from the shared memory and sends it up through the TCP/IP stack. There is no twisted-pair cable or other media since the shared memory acts as the transfer media. A shared mailbox holds the packet length and sends an interrupt to one processor when written, while a general-purpose input-output GPIO module sends an interrupt to the other processor. The internal emulated-Ethernet is entirely within the phone and separate from cellular networks.

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Sunnyvale, CA, United States of America

Sai K Pothana