| 3 | | Blah blah |
| | 3 | The backlight is control by ioctl() calls on /dev/disp. All calls take the form |
| | 4 | |
| | 5 | {{{ |
| | 6 | typedef struct { |
| | 7 | int reg; |
| | 8 | int val; |
| | 9 | int par1; |
| | 10 | int par2; |
| | 11 | } lcd_disp_t; |
| | 12 | |
| | 13 | |
| | 14 | int op = /* operation code */ |
| | 15 | lcd_disp_t t = { /* parameters*/ }; |
| | 16 | int f = open (DEV_DISP, O_RDONLY); |
| | 17 | ioctl (f, op, &t); |
| | 18 | }}} |
| | 19 | |
| | 20 | The following operation codes are useful |
| | 21 | |
| | 22 | {{{ |
| | 23 | // Set brightness |
| | 24 | #define DISP_SET_BCKL_LEV _IOWR ( 'D', 9, lcd_disp_t*) |
| | 25 | // Enable display hardware |
| | 26 | #define DISP_ENABLE_DISP _IOWR ( 'D', 10, lcd_disp_t*) |
| | 27 | // Enable backlight |
| | 28 | #define DISP_ENABLE_BCKL _IOWR ( 'D', 11, lcd_disp_t*) |
| | 29 | }}} |
| | 30 | |
| | 31 | |
| | 32 | Each of these takes a single value in the par1 member of struct lcd_disp_t. Parameter values are as follows: |
| | 33 | |
| | 34 | DISP_ENABLE_DISP: 1 (on) or 0 (off) |
| | 35 | |
| | 36 | DISP_ENABLE_BCKL: 1 (on) or 0 (off) |
| | 37 | |
| | 38 | DISP_SET_BCKL_LEVEl: 0 (off) to probably 500. |
| | 39 | |
| | 40 | There is some uncertainty about what values are appropriate for display brightness. Minimum brightness is 1, and maximum is probably 500, although there does not appear to be a uniform spread of useful values between these extremes. There isn't a huge range of brightness anyway. AVOS only provides 3 levels and, although there probably are more, it isn't obvious that there are _usefully_ more. |
| | 41 | |
| | 42 | |
| | 43 | The display power itself is controlled by ioctl() calls on the framebuffer device /dev/fb. I am unsure of the exact purpose of all of these. However, the following piece of code, derived from a sample provided by Archos, should shut the display and backlight down completely. |
| | 44 | |
| | 45 | {{{ |
| | 46 | #define FBIO_OUTPUT_ENABLE _IOW ( 'F', 0x25, u_int32_t) |
| | 47 | #define VESA_NOBLANKING 0 |
| | 48 | #define VESA_POWERDOWN 3 |
| | 49 | #define FBIOBLANK 0x4611 |
| | 50 | #define FB_BLANK_POWERDOWN VESA_POWERDOWN + 1 |
| | 51 | #define FB_BLANK_NORMAL VESA_NOBLANKING + 1 |
| | 52 | #define FB_BLANK_UNBLANK VESA_NOBLANKING + 0 |
| | 53 | |
| | 54 | void turnOffDisplay() |
| | 55 | { |
| | 56 | int osd_fd = open (DEV_FB, O_RDONLY); |
| | 57 | if (osd_fd <= 0) |
| | 58 | { |
| | 59 | // Handle error |
| | 60 | return; |
| | 61 | } |
| | 62 | int disp_fd = open (DEV_DISP, O_RDONLY); |
| | 63 | if (disp_fd <= 0) |
| | 64 | { |
| | 65 | close (osd_fd); |
| | 66 | // Handle error |
| | 67 | return; |
| | 68 | } |
| | 69 | int fls = 0; |
| | 70 | lcd_disp_t lcdOff = { .par1 = 0 }; |
| | 71 | ioctl (disp_fd, DISP_ENABLE_BCKL, &lcdOff); |
| | 72 | ioctl (osd_fd, FBIO_GFX_LAYER_ENABLE, &fls); |
| | 73 | ioctl (osd_fd, FBIOBLANK, FB_BLANK_POWERDOWN); |
| | 74 | ioctl (osd_fd, FBIO_OUTPUT_ENABLE, &fls); |
| | 75 | ioctl (disp_fd, DISP_ENABLE_DISP, &lcdOff); |
| | 76 | } |
| | 77 | }}} |
| | 78 | |
| | 79 | And to switch it back on again: |
| | 80 | |
| | 81 | {{{ |
| | 82 | void turnOnDisplay() |
| | 83 | { |
| | 84 | int osd_fd = open (DEV_FB, O_RDONLY); |
| | 85 | if (osd_fd <= 0) |
| | 86 | { |
| | 87 | // Handle error |
| | 88 | return; |
| | 89 | } |
| | 90 | int disp_fd = open (DEV_DISP, O_RDONLY); |
| | 91 | if (disp_fd <= 0) |
| | 92 | { |
| | 93 | // Handle error |
| | 94 | close (osd_fd); |
| | 95 | return; |
| | 96 | } |
| | 97 | int t = 1; |
| | 98 | lcd_disp_t lcdOn = { .par1 = 1 }; |
| | 99 | ioctl (disp_fd, DISP_ENABLE_DISP, &lcdOn); |
| | 100 | ioctl (osd_fd, FBIO_OUTPUT_ENABLE, &t); |
| | 101 | ioctl (osd_fd, FBIOBLANK, FB_BLANK_UNBLANK); |
| | 102 | ioctl (osd_fd, FBIO_GFX_LAYER_ENABLE, &t); |
| | 103 | ioctl (disp_fd, DISP_ENABLE_BCKL, &lcdOn); |
| | 104 | close (osd_fd); |
| | 105 | close (disp_fd); |
| | 106 | } |
| | 107 | }}} |
| | 108 | |
| | 109 | Note that the backlight level and backlight on/off status are independent. This is very important because, so far as I know, there is no way to _read_ the backlight level from the Archos driver. So applications that switch the backlight for power saving can do so, to some extent, without changing the user's preferred brightness. |
| | 110 | |
