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firmware: improve DDMTD resolution using dithering/averaging

This commit is contained in:
Sebastien Bourdeauducq 2019-01-28 16:03:40 +08:00
parent cfe66549ff
commit 3acee87df2
1 changed files with 28 additions and 20 deletions
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48
artiq/firmware/libboard_artiq/jesd204sync.rs
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@ -22,7 +22,10 @@ fn average_phases(phases: &[i32], modulo: i32) -> i32 {
} }
} }
const DDMTD_N_SHIFT: i32 = 6; const RAW_DDMTD_N_SHIFT: i32 = 6;
const RAW_DDMTD_N: i32 = 1 << RAW_DDMTD_N_SHIFT;
const DDMTD_DITHER_BITS: i32 = 1;
const DDMTD_N_SHIFT: i32 = RAW_DDMTD_N_SHIFT + DDMTD_DITHER_BITS;
const DDMTD_N: i32 = 1 << DDMTD_N_SHIFT; const DDMTD_N: i32 = 1 << DDMTD_N_SHIFT;
fn measure_ddmdt_phase_raw() -> i32 { fn measure_ddmdt_phase_raw() -> i32 {
@ -30,37 +33,41 @@ fn measure_ddmdt_phase_raw() -> i32 {
} }
fn measure_ddmdt_phase() -> i32 { fn measure_ddmdt_phase() -> i32 {
const AVG_PRECISION_SHIFT: i32 = 5; const AVG_PRECISION_SHIFT: i32 = 6;
const AVG_PRECISION: i32 = 1 << AVG_PRECISION_SHIFT; const AVG_PRECISION: i32 = 1 << AVG_PRECISION_SHIFT;
const AVG_MOD: i32 = 1 << (DDMTD_N_SHIFT + AVG_PRECISION_SHIFT); const AVG_MOD: i32 = 1 << (RAW_DDMTD_N_SHIFT + AVG_PRECISION_SHIFT + DDMTD_DITHER_BITS);
let mut measurements = [0; AVG_PRECISION as usize]; let mut measurements = [0; AVG_PRECISION as usize];
for i in 0..AVG_PRECISION { for i in 0..AVG_PRECISION {
measurements[i as usize] = measure_ddmdt_phase_raw() << AVG_PRECISION_SHIFT; measurements[i as usize] = measure_ddmdt_phase_raw() << (AVG_PRECISION_SHIFT + DDMTD_DITHER_BITS);
clock::spin_us(10); clock::spin_us(10);
} }
average_phases(&measurements, AVG_MOD) >> AVG_PRECISION_SHIFT average_phases(&measurements, AVG_MOD) >> AVG_PRECISION_SHIFT
} }
fn test_ddmtd_stability() -> Result<(), &'static str> { fn test_ddmtd_stability(raw: bool, tolerance: i32) -> Result<(), &'static str> {
let tolerance = 4; info!("testing DDMTD stability (raw={}, tolerance={})...", raw, tolerance);
info!("testing DDMTD stability..."); let modulo = if raw { RAW_DDMTD_N } else { DDMTD_N };
let measurement = if raw { measure_ddmdt_phase_raw } else { measure_ddmdt_phase };
let ntests = if raw { 250000 } else { 150 };
let mut max_pkpk = 0; let mut max_pkpk = 0;
for _ in 0..32 { for _ in 0..32 {
let modulo_fix_ref = measure_ddmdt_phase(); // If we are near the edges, wraparound can throw off the simple min/max computation.
let modulo_fix = // In this case, add an offset to get near the center.
if modulo_fix_ref < DDMTD_N/4 || (modulo_fix_ref > 3*DDMTD_N/4) { let quadrant = measure_ddmdt_phase();
DDMTD_N/2 let center_offset =
if quadrant < DDMTD_N/4 || quadrant > 3*DDMTD_N/4 {
modulo/2
} else { } else {
0 0
}; };
let mut min = DDMTD_N; let mut min = modulo;
let mut max = 0; let mut max = 0;
for _ in 0..500000 { for _ in 0..ntests {
let m = (measure_ddmdt_phase_raw() + modulo_fix) % DDMTD_N; let m = (measurement() + center_offset) % modulo;
if m < min { if m < min {
min = m; min = m;
} }
@ -73,8 +80,8 @@ fn test_ddmtd_stability() -> Result<(), &'static str> {
max_pkpk = pkpk; max_pkpk = pkpk;
} }
if pkpk > tolerance { if pkpk > tolerance {
error!(" ...excessive peak-peak jitter: {} (min={} max={} modulo_fix={})", pkpk, error!(" ...excessive peak-peak jitter: {} (min={} max={} center_offset={})", pkpk,
min, max, modulo_fix); min, max, center_offset);
return Err("excessive DDMTD peak-peak jitter"); return Err("excessive DDMTD peak-peak jitter");
} }
hmc7043::sysref_slip(); hmc7043::sysref_slip();
@ -86,7 +93,7 @@ fn test_ddmtd_stability() -> Result<(), &'static str> {
fn test_slip_ddmtd() -> Result<(), &'static str> { fn test_slip_ddmtd() -> Result<(), &'static str> {
// expected_step = (RTIO clock frequency)*(DDMTD N)/(HMC7043 CLKIN frequency) // expected_step = (RTIO clock frequency)*(DDMTD N)/(HMC7043 CLKIN frequency)
let expected_step = 4; let expected_step = 8;
let tolerance = 1; let tolerance = 1;
info!("testing HMC7043 SYSREF slip against DDMTD..."); info!("testing HMC7043 SYSREF slip against DDMTD...");
@ -187,7 +194,7 @@ fn calibrate_sysref_target(rising_average: i32, falling_average: i32) -> Result<
((falling_average - (DDMTD_N - rising_average))/2 + DDMTD_N) % DDMTD_N ((falling_average - (DDMTD_N - rising_average))/2 + DDMTD_N) % DDMTD_N
}; };
info!("SYSREF calibration coarse target: {}", coarse_target); info!("SYSREF calibration coarse target: {}", coarse_target);
reach_sysref_ddmtd_target(coarse_target, 2)?; reach_sysref_ddmtd_target(coarse_target, 4)?;
let target = measure_ddmdt_phase(); let target = measure_ddmdt_phase();
info!("SYSREF calibrated target: {}", target); info!("SYSREF calibrated target: {}", target);
Ok(target) Ok(target)
@ -227,7 +234,8 @@ pub fn sysref_rtio_align() -> Result<(), &'static str> {
} }
pub fn sysref_auto_rtio_align() -> Result<(), &'static str> { pub fn sysref_auto_rtio_align() -> Result<(), &'static str> {
test_ddmtd_stability()?; test_ddmtd_stability(true, 4)?;
test_ddmtd_stability(false, 1)?;
test_slip_ddmtd()?; test_slip_ddmtd()?;
let sysref_sh_limits = measure_sysref_sh_limits()?; let sysref_sh_limits = measure_sysref_sh_limits()?;
@ -262,7 +270,7 @@ pub fn sysref_auto_rtio_align() -> Result<(), &'static str> {
} }
}; };
reach_sysref_ddmtd_target(target_phase, 1)?; reach_sysref_ddmtd_target(target_phase, 3)?;
if sysref_sh_error() { if sysref_sh_error() {
return Err("SYSREF does not meet S/H timing at DDMTD phase target"); return Err("SYSREF does not meet S/H timing at DDMTD phase target");
} }