Hold DMA upsizer output under backpressure

[flaviens]

Summary

• Backpressure the sample input while a packed output is pending.
• Hold output valid, data, and packet state through handshake.
• Keep all stream-app RTL variants aligned.

The upsizers tied input ready high while pulsing output valid for one cycle. A stalled DMA sink could therefore lose packed words, overwrite buffered samples, and retain TLAST into a later packet.

Checks

• Icarus backpressure regression: upstream accepted 12 samples but returned 1 word; fixed RTL returned all 3 words with no payload or packet-state errors.
• Icarus partial-packet regression: fixed RTL realigned the next packet with no payload or TLAST errors.
• All six modified modules compile with Icarus.

[Copilot]

Pull request overview

This PR updates the DMA S2MM “upsizer” RTL blocks to properly apply backpressure to the input stream while an output word is pending, and to hold output TVALID/data/packet state stable until the downstream handshake completes. This prevents packed output words (and TLAST state) from being lost or mis-associated when the DMA sink stalls.

Changes:

• Gate s_axis_tready with (~m_axis_tvalid | m_axis_tready) and introduce input_transfer / output_transfer / word_complete handshake helpers.
• Hold m_axis_tvalid asserted until m_axis_tready is observed, and update/clear tlast in sync with completed-word handshakes.
• Apply the same handshake/backpressure behavior consistently across rtl / rtl_4ch / rtl_250 stream-app variants.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
prj/stream_app/rtl/rtl/rp_oscilloscope/rp_dma_s2mm_upsize.v	Adds proper input backpressure and holds output valid/state through handshake for oscilloscope upsizer.
prj/stream_app/rtl/rtl/rp_gpio/gpio_dma_s2mm_upsize.v	Adds proper input backpressure and holds output valid/state through handshake for GPIO upsizer.
prj/stream_app/rtl/rtl_4ch/rp_oscilloscope/rp_dma_s2mm_upsize.v	Mirrors oscilloscope upsizer backpressure/hold semantics in 4ch variant.
prj/stream_app/rtl/rtl_4ch/rp_gpio/gpio_dma_s2mm_upsize.v	Mirrors GPIO upsizer backpressure/hold semantics in 4ch variant.
prj/stream_app/rtl/rtl_250/rp_oscilloscope/rp_dma_s2mm_upsize.v	Mirrors oscilloscope upsizer backpressure/hold semantics in 250MHz variant.
prj/stream_app/rtl/rtl_250/rp_gpio/gpio_dma_s2mm_upsize.v	Mirrors GPIO upsizer backpressure/hold semantics in 250MHz variant.

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