| Programmer's View of Cpia2 |
| |
| Cpia2 is the second generation video coprocessor from VLSI Vision Ltd (now a |
| division of ST Microelectronics). There are two versions. The first is the |
| STV0672, which is capable of up to 30 frames per second (fps) in frame sizes |
| up to CIF, and 15 fps for VGA frames. The STV0676 is an improved version, |
| which can handle up to 30 fps VGA. Both coprocessors can be attached to two |
| CMOS sensors - the vvl6410 CIF sensor and the vvl6500 VGA sensor. These will |
| be referred to as the 410 and the 500 sensors, or the CIF and VGA sensors. |
| |
| The two chipsets operate almost identically. The core is an 8051 processor, |
| running two different versions of firmware. The 672 runs the VP4 video |
| processor code, the 676 runs VP5. There are a few differences in register |
| mappings for the two chips. In these cases, the symbols defined in the |
| header files are marked with VP4 or VP5 as part of the symbol name. |
| |
| The cameras appear externally as three sets of registers. Setting register |
| values is the only way to control the camera. Some settings are |
| interdependant, such as the sequence required to power up the camera. I will |
| try to make note of all of these cases. |
| |
| The register sets are called blocks. Block 0 is the system block. This |
| section is always powered on when the camera is plugged in. It contains |
| registers that control housekeeping functions such as powering up the video |
| processor. The video processor is the VP block. These registers control |
| how the video from the sensor is processed. Examples are timing registers, |
| user mode (vga, qvga), scaling, cropping, framerates, and so on. The last |
| block is the video compressor (VC). The video stream sent from the camera is |
| compressed as Motion JPEG (JPEGA). The VC controls all of the compression |
| parameters. Looking at the file cpia2_registers.h, you can get a full view |
| of these registers and the possible values for most of them. |
| |
| One or more registers can be set or read by sending a usb control message to |
| the camera. There are three modes for this. Block mode requests a number |
| of contiguous registers. Random mode reads or writes random registers with |
| a tuple structure containing address/value pairs. The repeat mode is only |
| used by VP4 to load a firmware patch. It contains a starting address and |
| a sequence of bytes to be written into a gpio port. |