diff options
Diffstat (limited to 'fw/transpose.c')
| -rw-r--r-- | fw/transpose.c | 47 |
1 files changed, 45 insertions, 2 deletions
diff --git a/fw/transpose.c b/fw/transpose.c index a6c7e71..7af3e8e 100644 --- a/fw/transpose.c +++ b/fw/transpose.c @@ -4,14 +4,52 @@ #include "transpose.h" +/* This file contains conversion routines that pre-format the brightness data + * received from the UART such that the interrupt service routines only need to + * push it out the SPI without further computation, making these ISRs nice and + * tight. + * + * To understand this code note the multiplexing scheme used on the board. The + * circuit contains two MBI5026 shift-register LED drivers of 16 channels each + * cascaded. Effectively this behaves like a 32-channel LED driver fed data + * serially. Each output is connected to a single digit's COM pin. All digit's + * segment anode pins are connected together in a large bus fed by one of the + * two auxiliary shift registers. + * + * The firmware is selecting each segment in turn with a full BCM cycle for each + * segment before the next one is selected. + */ + +/* This array maps the 32 adressable digits on a board to the 32 bits shifted + * out to the LED drivers. */ uint8_t digit_map[33] = { 0, 1, 2, 3, 28,29,30,31, 4, 5, 6, 7, 24,25,26,27, 8, 9,10,11, 20,21,22,23, 12,13,14,15, 16,17,18,19 }; -void transpose_data(volatile uint8_t *rx_buf, volatile struct framebuf *out_fb) { + +/* This function produces a 10-bit output buffer ready for the modulation ISRs + * from 10-bit input data encoded for the UART. For the precise data format, see + * transpose.h. + * + * On the UART side we have digits in the order defined in digit_map, 10 byte + * per digit. The first 8 bytes are the 8 LSBs of each segments brightness value + * in the order [A, B, C, D, E, F, G, DECIMAL_POINT]. The two MSBs to make each + * value 10-bit are bit-packed into the remaining two bytes in big-endian byte + * order starting from DP. + * + * On the display frame buffer side, data is stored in multiplexing order: + * first digits, then time/bits and finally segments. So for each segment you + * have a large buffer containing all the bit periods and digits, and for each + * bit period you have 32 bits for all 32 digits. + */ +void transpose_data(volatile uint8_t *rx_buf, volatile struct framebuf *out_fb) +{ + /* FIXME this can probably be removed. */ memset((uint8_t *)out_fb, 0, sizeof(*out_fb)); + + /* 8 MSB loop */ struct data_format *rxp = (struct data_format *)rx_buf; for (int bit=0; bit<8; bit++) { /* bits */ uint32_t bit_mask = 1U<<bit; @@ -27,6 +65,8 @@ void transpose_data(volatile uint8_t *rx_buf, volatile struct framebuf *out_fb) *outp = acc; } } + + /* 2 packed LSB loop */ for (int bit=0; bit<2; bit++) { /* bits */ volatile uint32_t *frame_data = out_fb->frame[bit].data; for (int seg=0; seg<8; seg++) { /* segments */ @@ -40,10 +80,13 @@ void transpose_data(volatile uint8_t *rx_buf, volatile struct framebuf *out_fb) frame_data[seg] = acc; } } + + /* Global analog brightness value */ out_fb->brightness = ((volatile struct framebuf *)rx_buf)->brightness; } - +/* This function was used for testing transpose_data. It does precisely the + * reverse operation. */ void untranspose_data(struct framebuf *fb, uint8_t *txbuf) { memset(txbuf, 0, sizeof(*fb)); |