diff --git a/src/class/audio/audio_device.c b/src/class/audio/audio_device.c index 0828f2e6..5ca95658 100644 --- a/src/class/audio/audio_device.c +++ b/src/class/audio/audio_device.c @@ -310,7 +310,8 @@ typedef struct #if CFG_TUD_AUDIO_ENABLE_FEEDBACK_DETERMINATION_WITHIN_SOF_ISR uint8_t n_frames; // Number of (micro)frames used to estimate feedback value uint8_t n_frames_current; // Current (micro)frame number - uint32_t feeback_param_factor; // TODO: Set this value within some new tud_audio_set_feedback_params_fm_fs function as feeback_param_factor = f_s / (f_cpu * n_frames)! + uint32_t feeback_param_factor_N; // Numerator of feedback parameter coefficient + uint32_t feeback_param_factor_D; // Denominator of feedback parameter coefficient #endif #endif @@ -2004,12 +2005,16 @@ bool audiod_xfer_cb(uint8_t rhport, uint8_t ep_addr, xfer_result_t result, uint3 } #if CFG_TUD_AUDIO_ENABLE_EP_OUT && CFG_TUD_AUDIO_ENABLE_FEEDBACK_EP && CFG_TUD_AUDIO_ENABLE_FEEDBACK_DETERMINATION_WITHIN_SOF_ISR +// f_s max is 2^19-1 = 524287 Hz +// n_frames_min is ceil(2^10 * f_s / f_m) for full speed and ceil(2^13 * f_s / f_m) for high speed +// f_m max is 2^29/(1 ms * n_frames) for full speed and 2^29/(125 us * n_frames) for high speed bool tud_audio_set_feedback_params_fm_fs(uint8_t func_id, uint32_t f_m, uint32_t f_s) { audiod_function_t* audio = &_audiod_fct[func_id]; uint8_t n_frame = 1; // TODO: finalize that audio->n_frames = n_frame; - audio->feeback_param_factor = f_s / f_m / n_frame; // TODO: Check the 16.16 precision! + audio->feeback_param_factor_N = f_s << 13; + audio->feeback_param_factor_D = f_m * n_frame; return true; } #endif @@ -2023,7 +2028,7 @@ void audiod_sof (uint8_t rhport, uint32_t frame_count) // Determine feedback value - The feedback method is described in 5.12.4.2 of the USB 2.0 spec // Boiled down, the feedback value Ff = n_samples / (micro)frame. - // Since an accuracy of less than 1 Sample / second is desired, at least n_frames = ceil(2^K * f_s / f_cpu) frames need to be measured, where K = 10 for full speed and K = 13 for high speed, f_s is the sampling frequency e.g. 48 kHz and f_cpu is the cpu clock frequency e.g. 100 MHz (or any other master clock whose clock count is available and locked to f_s) + // Since an accuracy of less than 1 Sample / second is desired, at least n_frames = ceil(2^K * f_s / f_m) frames need to be measured, where K = 10 for full speed and K = 13 for high speed, f_s is the sampling frequency e.g. 48 kHz and f_cpu is the cpu clock frequency e.g. 100 MHz (or any other master clock whose clock count is available and locked to f_s) // The update interval in the (4.10.2.1) Feedback Endpoint Descriptor must be less or equal to 2^(K - P), where P = min( ceil(log2(f_cpu / f_s)), K) // Ff = n_cycles / n_frames * f_s / f_cpu in 16.16 format, where n_cycles are the number of CPU cycles within n_frames @@ -2038,7 +2043,7 @@ void audiod_sof (uint8_t rhport, uint32_t frame_count) if (audio->n_frames_current == audio->n_frames) { uint32_t n_cylces = tud_audio_n_get_fm_n_cycles_cb(rhport, audio->ep_fb); - uint32_t feedback = n_cylces * audio->feeback_param_factor; + uint32_t feedback = (n_cylces << 3) * audio->feeback_param_factor_N / audio->feeback_param_factor_D; // feeback_param_factor_N has scaling factor of 13 bits, n_cycles 3 and feeback_param_factor_D 1, hence 16.16 precision tud_audio_n_fb_set(i, feedback); audio->n_frames_current = 0;