mirror of
https://github.com/halleysfifthinc/AVCLAN-Mockingboard.git
synced 2026-08-07 01:13:18 +00:00
Allen Hill
85 lines
2.8 KiB
C
85 lines
2.8 KiB
C
#include <avr/io.h>
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#include <avr/sfr_defs.h>
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// char AC0_STATUS_STATE_bm = (1<<4);
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#define MAXMSGLEN 32
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uint8_t message[32];
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uint8_t current_uint8_t;
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uint8_t nbits;
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typedef struct AVCLAN_frame_struct {
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uint16_t sender_addr; // formerly "master"
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uint16_t receiver_addr; // formerly "slave"
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uint8_t control;
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uint8_t length;
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uint8_t data[MAXMSGLEN];
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} AVCLAN_frame_t;
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int8_t AVCLAN_read_data(uint8_t *data, uint8_t nbits) {
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int8_t parity = 0;
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uint8_t bits = 0;
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while (bits < nbits) {
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loop_until_bit_is_set(TCB0.INTFLAGS, 0);
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uint16_t period = TCB0.CNT;
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uint16_t pulse = TCB0.CCMP;
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if ((period - pulse) < 0x033) {
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(*data)++;
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parity++;
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}
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bits++;
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if ((bits ^ 0x08) == 1) {
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data++;
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}
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}
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return parity;
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}
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int8_t AVCLAN_read_data_asm(uint8_t *data, uint8_t nbits) {
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int8_t parity = 0;
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uint8_t bits = 0;
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uint8_t uint8_t = data[0];
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while (bits < nbits) {
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loop_until_bit_is_set(TCB0.INTFLAGS, 0);
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__asm__ __volatile__(
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"sub %A[tcb],%C[tcb] ; TCB0_CNT - TCB0_CCMP (low) \n\t"
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"sbc %B[tcb],%D[tcb] ; TCB0_CNT - TCB0_CCMP (high) \n\t"
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"cp %A[tcb],lo8(thresh) ; Compare low \n\t"
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"cpc %B[tcb],hi8(thresh) ; Compare high; carry flag is set if "
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"(TCB_CNT - TCB_CCMP) < half_per (ie read bit is 0x01)\n\t"
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"brcc skipparity ; Skip incrementing parity if bit was 0 "
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"\n\t"
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"inc %[parity] ; Increment parity (doesn't change carry "
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"flag) \n"
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"skipparity: \n\t"
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"rol %[data] ; Rotate left with carry flag \n\t"
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"inc %[bits] ; Increment \n\t"
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"mov __tmp_reg__,%[bits] ; Copy to temp registry to avoid messing "
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"with loop count \n\t"
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"eor __tmp_reg__,$0x09 ; Reset if greater than 8 \n\t"
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"brbc 1,end ; The current uint8_t read was just "
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"completed; increment the pointer \n\t"
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"std %a[data_ADDR]+,%[data] ; \n"
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"end: \n\t"
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: [data_ADDR] "+e"(data), [bits] "+r"(bits), [parity] "+r"(parity)
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: [tcb] "r"(_SFR_MEM32(
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&TCB0_CNT)), // TCB0_CNT and TCB0_CCMP are consecutive uint16_t.
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// Load address of TCB0_CNT and access both words
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// using offsets from that pointer
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[data] "r"(uint8_t),
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[thresh] "M"(0x0033) // Length of synchronization period (~20us) plus
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// fudge factor to distinguish `0` (~20us +
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// ~13us) from `1` (~20us)
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: "memory");
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}
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return parity;
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}
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int main() {
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uint8_t message[2];
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uint16_t master;
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int8_t parity = AVCLAN_read_data((uint8_t *)(&message), 16);
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parity = AVCLAN_read_data_asm((uint8_t *)(&master), 12);
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} |